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- Published: 20 January 2023
Exercising is good for the brain but exercising outside is potentially better
- Katherine Boere 1 ,
- Kelsey Lloyd 1 ,
- Gordon Binsted 2 &
- Olave E. Krigolson 1
Scientific Reports volume 13 , Article number: 1140 ( 2023 ) Cite this article
- Cognitive control
- Health policy
- Human behaviour
It is well known that exercise increases cognitive function. However, the environment in which the exercise is performed may be just as important as the exercise itself. Time spent in natural outdoor environments has been found to lead to increases in cognition similar to those resulting from acute exercise. Therefore, the benefits of both exercise and nature exposure suggest an additive impact on brain function when both factors are combined. This raises the question: what is the interaction between acute exercise and environment on cognition? We answered this question using electroencephalography to probe cognitive function using the oddball task before and after brief indoor and outdoor walks on 30 participants (average 21 years old, 95% CI [20, 22]). Our results demonstrate improved performance and an increase in the amplitude of the P300, an event-related neural response commonly associated with attention and working memory, following a 15-min walk outside; a result not seen following a 15-min walk inside. Importantly, this finding indicates that the environment may play a more substantial role in increasing cognitive function such as attention than exercise, at least in terms of acute exercise (i.e., a brief walk). With the world’s growing urbanization and the associated increase in sedentary time indoors, a deeper understanding of how these factors interact and influence cognition may be critical to combat adverse health effects.
It is well known that exercise generally enhances cognitive function 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 . However, the environment in which exercise is performed may be just as important as the exercise itself 11 , 12 , 13 . A growing body of research highlights nature's positive impacts on improving cognition and mental health 14 , 15 , 16 . Thus, with considerable evidence to support the benefits of exercise and being in nature, it is logical to expect that combining these two factors would lead to an ever-greater overall increase in cognition. Indeed, evidence supports this supposition: exercising outdoors in natural environments produces more benefits to the brain than exercising indoors 12 , 17 , 18 , 19 , 20 , 21 , 22 , 23 . Yet the findings are unclear for acute exercise durations under 20 min. This raises the question: How does the environment influence cognitive function for a brief exercise period? Gaining a deeper understanding of these underlying influences on the brain is important to combat the world’s growing urbanization and the associated increase in the amount of time spent indoors 24 .
In terms of cognition, acute outdoor exercise has primarily been found to enhance executive functions dependent on the prefrontal cortex, such as attention, working memory, and inhibitory control 1 , 3 . For instance, Bailey and colleagues 19 found that participants who walked in an outdoor natural environment performed significantly better on a cognitive task—the Stroop task—than those who walked inside. These findings are further supported by Berman et al. 20 , who had participants complete a different cognitive task (the backwards digit span task) before and after a 35-min walk in a forest or an urban environment. In a key manipulation, the researchers induced cognitive fatigue in participants by having them complete a rigorous memory task before walking. Berman and colleagues’ results showed that on the cognitive task performed after the walk, participants who walked in the forest performed better than those who had walked in an urban environment suggesting that nature played an essential role in restoring the cognitive resources that were depleted by the memory task 20 . Together, these results provide evidence that outdoor exercise enhances executive function to a greater extent than indoor exercise.
Neuroimaging has provided key insight into the impact of acute exercise on the brain. Research with functional magnetic resonance imaging and functional near-infrared spectroscopy (fNIRS) has demonstrated that acute exercise drives improvements in cognition via increased cerebral blood flow (CBF) to the prefrontal cortex 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 . For example, Yanagisawa and colleagues used fNIRS to examine brain regions activated through acute exercise-induced enhancements in cognitive performance 27 . The researchers found that acute moderate exercise improved performance on the Stroop task and elicited increased activation in the dorsolateral prefrontal cortex- a region explicitly associated with executive function 27 . In addition, a range of neurotransmitters have been implicated in acute exercise's signalling pathways that induce positive cognitive and mood effects 1 , 3 , 28 , 29 , 30 , 31 , 32 . Specifically, several studies have found increases in dopamine, epinephrine, and norepinephrine in the prefrontal cortex post-exercise; all indicated to be involved in neuromodulating behaviours such as attention, reward, learning, and memory 29 , 30 , 31 , 32 , 33 . Collectively, these findings highlight the impact of acute exercise on the prefrontal cortex and indicate several mechanisms by which acute exercise influences the neurophysiology of this process.
Here we used neuroimaging to investigate the interaction of brief exercise and environment on cognition. Specifically, we utilized mobile electroencephalography (mEEG) to measure indices of cognitive performance prior to and after brief 15-min indoor and outdoor walks. Before and after each walk, participants completed a standard visual oddball task while mEEG data was recorded. Based on the abundance of literature indicating that exercise enhances cognitive performance 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , we hypothesized that we would see an increase in the amplitude of the P300—a component of the human event-related brain potential (ERP) associated with working memory and attention—following exercise. Additionally, given the well-documented positive effects of nature on the brain 14 , 15 , 16 , we further hypothesized that the increase in the amplitude of the P300 would be greater following exercise outside than the following exercise inside.
To investigate the impact of walking location, we conducted a two (location: inside versus outside) by two (time: pre-test versus post-test) fully repeated measures analysis of variance on reaction time, accuracy, and P300 amplitude. See Table 1 for a summary of results.
An analysis of reaction time revealed a main effect for time (F(1,29) = 11.01, p = 0.002, η 2 = 0.275) that showed that reaction decreased slightly following 15 min of walking (see Fig. 1 ). This was qualified by an interaction between walking location and time (F(1,29) = 3.95, p = 0.05, η 2 = − 0.120). Decomposition of the interaction revealed that reaction time decreased after a 15 min outdoor walk (t(29) = 5.07, p = 0.000, d = 0.926) but not following a 15 min indoor walk (t(29) = 0.84, p = 0.409, d = 0.152). We did not find a main effect for walking location (p > 0.05).
The difference in reaction time and accuracy on the oddball task between pre- and post- indoor and outdoor walk. Value on plot = post walk score − pre-walk score . Therefore, negative values indicate improved performance. Error bars reflect 95% within-subject confidence intervals.
Our analysis of our accuracy data (number of errors made) revealed no main effects or interactions (F(1,29) = 3.59, p > 0.05, η 2 = 0.10, see Fig. 1 ).
Here, we found a main effect of time (F(1,29) = 12.40, p = 0.001, η 2 = 0.299) that revealed an increase in P300 amplitude following 15 min of walking. This was qualified by an interaction between walking location and time (F(1,29) = 5.62, p = 0.025, η 2 = 0.162). Decomposition of that interaction revealed no change in P300 amplitude following an indoor walk (t(29) = 0.23, p = 0.82, d = 0.032) but an increase in P300 amplitude following an outdoor walk (t(29) = 4.49, p < 0.001, d = 0.434, see Figs. 2 and 3 ). We did not find a main effect for walking location (p > 0.05).
Grand average ERP difference waveforms for the visual oddball pre-test and post-test for indoor and outdoor walks. Note the P300 ERP component increased in the post-test following outdoor walks.
The difference in P300 peak amplitude between the post-test and pre-test for indoor and outdoor walks. Individual data are plotted for each participant.
In the present study, we examined how the walking environment—indoors or outdoors—interacted with acute exercise to impact cognitive function, specifically the oddball task and P300 amplitude. As predicted, exercise enhanced our measures of cognition, as evidenced by the rise in the amplitude of the P300 ERP component. However, this only occurred when the exercise took place outdoors. The main effect of exercise was extended to the behavioural results for reaction time, showing an overall decrease in reaction time post-walk. Yet again, the decrease in reaction times only occurred for outdoor walks. No difference was found in accuracy between groups, and we propose this is due to the ease of task difficulty. Our result is broadly consistent with a large body of research demonstrating that acute exercise enhances cognitive performance 1 , 2 , 3 , 5 , 6 , 7 , 9 , 10 . Further, previous EEG studies have shown that acute exercise increases P300 amplitude during task performance—a result associated with enhanced attentional processes and working memory in the pre-frontal cortex 34 , 35 , 36 , 37 , 38 . Our results align with notable findings that acute exercise improves brain function and is further supported by the positive effects found on task performance.
More importantly, we also found that outdoor exercise had an additional impact on cognitive attentional scores. Specifically, we found that the amplitude of the P300 ERP component was greater following a walk outside relative to a walk inside. In addition, reaction times were lower for outdoor walks than for indoor ones. This result is consistent with both attention restoration theory 13 , 39 , 40 , 41 and previous findings supporting the idea that natural environments facilitate attention restoration during acute exercise 14 , 15 , 16 , 42 . The attentional restoration theory proposed by Kaplan 39 posits that natural environments provide a sense of "being away" from routines and inducing "soft fascination." Rather than dominating one's attention, nature restores mental capacities and enhances cognitive performance 41 , 42 . Further, Kaplan and Berman 20 proposed that natural environments restore directed attention, a shared resource that supports executive function in the prefrontal cortex.
Neurophysiologically, attention can be described as increased activity in a particular brain area involved in processing stimuli. As per the hemodynamic response, we assume increased activation signifies increased CBF in that specific brain region. For reference, the hemodynamic response is a homeostatic mechanism that replenishes the nutrients used by biological tissues by adjusting blood flow to areas of activity. Keeping in mind that this fresh, nutrient-rich blood is a limited resource—the attentional restoration theory implies that exposure to natural environments restores this mechanism by reducing unrequired increases in CBF. Regarding exercise’s effect on CBF, the reported results are mixed. We believe this is due to the amount of variability within exercise-based studies on the brain—as intensity, duration, and fitness are all significant factors that could influence the rate of CBF. However, when examining the effect of acute low-moderate intensity exercise , we identified abundant literature supporting that exercise increases CBF 1 , 2 , 5 , 7 , 25 , 26 , 27 , 28 . Indeed, with the lungs working harder during exercise, this oxygen surplus must be transported through the circulatory system. To facilitate this process, the body responds with a rise in heart rate and a widening of the arterial walls, thereby increasing blood flow globally, including to the brain. Taken together, we suggest that exercise increases CBF while the natural outdoor environments reduce and restore CBF mechanisms. Therefore, post-exercise and nature exposure, the effect of reduced blood flow to brain areas focused on irrelevant stimuli (brain areas not currently required) concurrently allows for increased blood flow and activation in areas pertinent to important stimuli (i.e., the task at hand).
An intriguing finding in our study is that we did not see a specific increase in the measured index of cognitive function following a brief walk indoors (i.e., we did not see an increase in P300 amplitude), nor did we find an increase in cognitive performance. This result conflicts with a significant meta-analysis by Chang and colleagues 3 and fails to support the previously stated inference that brief exercise (less than 20 min) could promote cognitive function. The results imply that environmental location may facilitate attention restoration and improve indices of cognition without exercise. Such impacts of both nature and acute exercise could be synergistic; however, this begs the question, which plays a more prominent role in improving cognition? Although we cannot conclude this without separating exercise and environment, our results point to a more substantial role of environment in increasing cognitive function. Our findings suggest that if one has only 15 min to exercise 24 , performing it outdoors appears to have a greater effect on ERP indices of attention and working memory than indoors.
Notably, there are limitations to the conclusions we can draw from our findings. First, there is a lack of objective exercise intensity measurement. Although the participants were clearly explained, demonstrated, and paced with the desired walking intensity, no heart rate monitor was used. We recommend that all future studies introduce heart rate monitoring and rate of perceived exertion to further control variability and increase the validity of results. Second, previous research suggests that exercise duration must be over 20 min to affect cognitive performance positively 1 , 3 , 6 . Here, the duration of the walking protocol was decided from preliminary pilot testing, which recorded the time it would take a student to walk at a low/moderate intensity around a set track of 2 km. This resulted in a walking protocol of roughly 15 min. In addition, we specifically sought to investigate if the effects of this exercise differ when undertaken outside. Indeed, this time constraint may be why we did not find significant exercise-induced cognitive improvements. However, from this perspective, if the exercise duration is not long enough to influence cognitive performance, it is reasonable to deduce that the remaining variable—the environment—may be the driving force in increasing P300 amplitudes.
Considering the constraints of using mEEG over traditional large array systems is also essential. On mEEG, electrodes are placed in non-standard positions for observing “classic” ERP components such as the P300. Offline analyses of the oddball task typically would have focused on a central line electrode Pz as opposed to TP9 and TP10. Due to the MUSE device not having an electrode at Pz, we were forced to make this adaption. However, this is not a significant concern as previous work in our laboratory has demonstrated that although this produces a slightly different waveform, it still reveals clearly observable and quantifiable ERP components 47 , 48 . Second, due to time lags inherent with Bluetooth data connection and the inability to insert experimental event markers, we know there is a notable “jitter” in the EEG data. Yet, our previous work demonstrates that this does not prevent the recording or quantification of ERP components—it simply adds a delay which is accounted for in our analysis 47 , 48 .
In conclusion, we demonstrate that a brief walk outside results in a greater increase in cognitive function than a short walk inside. Given the continued growth in urbanization and a move to an indoor lifestyle, our results highlight the importance of spending time in nature, especially when exercising. Indeed, in a world where many people “hit the gym” before or after work or on their lunch break, our results suggest that these people would be better served by simply “getting outside”.
All participants gave their informed written consent, approved by the Human Research Ethics Board at the University of Victoria (HREB: BC17-456). Human Research Ethics Board approved all experimental protocols at the University of Victoria (HREB: BC17-456). The experiment conformed to the ethical standards prescribed by the 1964 Declaration of Helsinki and subsequent revisions. All participants were given a comprehensive set of instructions regarding the procedure and tests, agreed both verbally and in the consent form to the testing procedures, and were given course credit in exchange for their participation.
Participants in the present study were undergraduate, and graduate students at the University of Victoria, British Columbia, Canada (n = 32). Previous work in our laboratory 43 conducted an ERP experiment with a sample size of 500 and found that detecting an ERP elicits a large effect size of 0.8, following recommendations from Cohen 44 . We conducted a power analysis for a repeated measures t test using this standardized effect size, an alpha of 0.05, and the desired power of 0.95, which yielded a prospective sample size of 25 participants. Moreover, our laboratory follows a protocol wherein ERP studies include a minimum of 30 participants, corresponding to a power of 0.99. It is important to note that participants with more than 50% of their data discarded due to excessive EEG artifacts were not included in our analysis. To avoid conducting underpowered research 45 , we kept testing participants until we had achieved our a priori set size of 30. Thus, the data presented here reflect the first 30 participants who met our EEG artifact criterion and resulted in the removal of two participants (n = 30; 21 females, average age: 21, 95% CI [20, 22]) Participants were asked to refrain from exercising and consuming alcohol for 24 h before testing. Further, each participant was instructed to abstain from eating or consuming caffeine two hours before testing. All participants had normal or corrected-to-normal vision and no known neurological impairments.
Apparatus and procedure
Participants completed a standard visual oddball task on an Apple iPad (Apple Inc., Cupertino, CA, USA). At the same time, EEG data were recorded from a 2016 Muse EEG system (Interaxon Inc., Toronto, ON, Canada). The task and recordings were collected prior to and after 15-min indoor and outdoor walks. Walks were conducted on two separate days, on average 2 days apart and no more than 1 week apart (range = 1–7 days). The first participant walked inside on day one and outside on day 2. Subsequent participants alternated the walk locations on a participant-to-participant basis. The study was held at one of three times: 10:15 am, 12 pm or 1:45 pm—in an effort to limit the effects of the daily circadian rhythm.
Here, we choose the oddball task, rather than the previously used Stroop task 19 , 20 , to expand the current scientific literature on this topic. Both tasks are highly well-known in cognitive neuroscience, and both have been previously used to measure selective attention capacity and working memory 1 , 2 , 3 , 4 , 19 , 36 , 38 . Therefore finding the same results with a different yet equally valid task would only provide additional power to the result. During performance of the oddball task, participants saw a series of blue (RGB value = [0, 0, 255]) and green (RGB value = [0, 255, 0]) colored circles that appeared for 800 ms in the center of a dark gray background (RGB value = [108, 108, 108]) on the iPad screen. Before the onset of the first circle and between the presentation of subsequent circles, a black (RGB value = [0, 0, 0]) fixation cross was presented for 200 to 500 ms. Participants were not told the frequency of the blue and green circles: blue appeared less frequently (oddball: 30%) than green circles (control: 70%). Stimulus order was randomized, with the constraint that the stimulus presentation software ensured that no more than two infrequent (oddball) circles appeared consecutively. Participants were instructed to quickly press the bottom left or right of the iPad screen when they saw one of the blue circles (oddball) and not respond when they saw the green circles (control). The circles were presented for 800–1200 ms, and the trial ended automatically on oddball trials in which the participants did not respond. Each trial began with a fixation cross as soon as the previous circle disappeared. Participants completed four blocks of 100 trials.
After completing the pre-walk oddball task, participants completed a brief walk inside the Engineering Lab Building or outside the Alumni Chip Trail at the University of Victoria. This trail was a green and lush forested path around the campus. For both locations, the distance of the walk was 2 km. Participants were asked to walk at their normal pace—above leisurely but not hard breathing. For this reason, participants’ walk times varied between 14 and 17 min, with an average of 15 min. In addition, participants were asked not to speak to anyone, use their cell phones or listen to music for the entirety of the walk. A research assistant timed each walk and walked approximately 10 m behind the participant, pacing them to ensure they maintained the same walking intensity. Aside from the experimenter's directional instructions to ensure the participant kept a set pace, there was no conversation between the experimenter and the participant. After completing the walk, participants completed the oddball task again. All EEG recording was done in a quiet room within the Engineering Lab Wing building.
EEG data were recorded from a Muse EEG headband (Muse Version: 2016) sampling at 256 Hz (see http://www.choosemuse.com for full technical specifications, see Fig. 4 ). The Muse EEG system has electrodes located analogously to FPz, AF7, AF8, TP9, and TP10, with FPz utilized as the reference electrode during recording. EEG data were recorded, and the visual oddball task was performed with the PEER iOS application ( https://brainwavesoftware.ca/ ). Note that the PEER application does not send event markers to the EEG headset as per a traditional ERP study 46 but instead reads the EEG data with known Bluetooth lag and jitter. Specifically, we have written MATLAB code that allows two-way communication via the OSC protocol to send markers to mark a continuous EEG recording. As such, we “marked” the EEG data at the exact onset time when the circles were drawn. Due to the Bluetooth lag, the EEG samples corresponding to this point in time did not arrive for 18–20 ms on average with a jitter of approximately 5 ms 47 , 48 . It is important to note that this jitter only impacted the initial signal locking between the MUSE system and our software and did not vary over time. In addition, the random delays in the temporal onset of our data collection would have a Gaussian distribution, and thus the lags would average out.
The 2016 Muse EEG system was made by InterAxon Inc with electrodes labelled AF7, AF8, TP9, and TP10. Reference electrode is labelled at FPz.
Further, while the timing onset via Bluetooth is not “guaranteed,”—the order of data packets is ( https://www.bluetooth.com/ ). Simply put, this means that all data points are guaranteed to be in the same order they were continuously collected in. As such, the averaging of temporal onset did not impact the present data as much as one might assume. Thus, the signal did not differ from trial to trial but from participant to participant. Signal quality was then inferred by examining the variance per second on each EEG channel, and data collection began when all channels had a variance per second less than 200. Finally, we have previously shown that this method still results in a reliable albeit diminished ERP response 47 , 48 (see these papers for full details on Bluetooth timing issues and delay/jitter data).
Data processing and analysis
Data were processed offline in MATLAB using EEGLAB 49 and custom code. We did not re-reference the continuous EEG data offline as our ERP analysis focused on the two posterior Muse electrodes (TP9 and TP10) referenced when recording electrode FPz. Continuous EEG data were filtered with a dual-pass Butterworth filter with a 0.1–30 Hz passband and a 60 Hz notch filter. A preliminary analysis of the data revealed no lateralized effects; further, we wanted to improve the signal-to-noise ratio of the ERP measures 50 , so we created a pooled frontal and a pooled posterior virtual electrode by averaging across the frontal (AF7 and AF8) and the rear (TP9 and TP10) electrodes, respectively. Our ERP analysis only focused on the new average posterior virtual electrode based on our previous work 47 , 48 . We also chose not to analyze the ERP effects for the frontal ERP channels as re-referencing the EEG data mirrors the components given the high correlation between the Muse EEG channels—see https://www.krigolsonlab.com/muse-research.html for exploratory analyses examining this issue that provided the rationale for the choices we made here.
After filtering, epochs of data from 200 ms before to 600 ms after stimulus onset (oddball, control) were extracted from the continuous EEG data. Segments were then baseline corrected using the 200 ms preceding stimulus onset. An artifact rejection algorithm was then implemented to remove noise and blink artifacts; this procedure discarded segments with an absolute difference of more than 60 μV (on average: 30% [28.5, 31.5]). Segments were then averaged for each participant's oddball and control trials, and a difference waveform was constructed by subtracting the average control from the average oddball ERP waveform. Grand average ERPs were generated by averaging all conditional (oddball, control) and difference waveforms for each participant and the peak component latencies were identified (N200: ~ 200 ms; P300: ~ 400 ms). N200 and P300 ERP component amplitudes and latencies were quantified at the participant level by finding the local minimal (N200: 150–250 ms) and local maximal (P300: 400–600 ms) voltage amplitudes within the windows mentioned above around the grand average component peaks. ERP peak amplitude data were statistically analyzed using a two (walk location: indoor, outdoor) by two (time: pre-test, post-test) fully repeated measures analysis of variance. Post-hoc decomposition of the interaction was done via dependent samples t tests. Reaction time was calculated as the time it took participants to press the screen after the stimulus circle was presented. Accuracy was defined by the number of errors made during the task (responses to control stimulus or no response to oddball stimulus). Finally, mean data for ERP and behavioural data are presented with 95% confidence intervals.
All processing scripts can be found at https://github.com/Neuro-Tools . The data that supports the findings of this study are available from https://osf.io/5m24j/ .
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Oken, B. S. & Chiappa, K. H. Statistical issues concerning computerized analysis of brainwave topography. Ann. Neurol. 19 , 493–494 (1986).
This research was supported by NSERC Discovery Grant (RGPIN 2016-0943).
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Boere, K., Lloyd, K., Binsted, G. et al. Exercising is good for the brain but exercising outside is potentially better. Sci Rep 13 , 1140 (2023). https://doi.org/10.1038/s41598-022-26093-2
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DOI : https://doi.org/10.1038/s41598-022-26093-2
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Increase health benefits of exercise by working out before breakfast – new research
Exercising before eating breakfast improves how the body responds to insulin and lowers people’s risk of type 2 diabetes and cardiovascular disease.
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- Published on Friday 18 October 2019
- Last updated on Saturday 19 October 2019
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According to a new study , published in the Journal of Clinical Endocrinology and Metabolism health scientists at the universities of Bath and Birmingham found that by changing the timing of when you eat and exercise, people can better control their blood sugar levels.
The six-week study, which involved thirty men classified as obese or overweight and compared results from two intervention groups (who ate breakfast before / after exercise) and a control group (who made no lifestyle changes), found that people who performed exercise before breakfast burned double the amount of fat than the group who exercised after breakfast.
They found that increased fat use is mainly due to lower insulin levels during exercise when people have fasted overnight, which means that they can use more of the fat from their fat tissue and the fat within their muscles as a fuel. To test proof-of-principle the initial study involved only men, but future studies will look to translate these findings for different groups including women.
Whilst this did not lead to any differences for weight loss over six weeks, it did have ‘profound and positive’ effects on their health because their bodies were better able to respond to insulin, keeping blood sugar levels under control and potentially lowering the risk of diabetes and heart disease.
Building on emerging evidence that the timing of meals in relation to exercise can shift how effective exercise is, the team behind this study wanted to focus on the impact on the fat stores in muscles for individuals who either worked out before or after eating and the effect this had on insulin response to feeding.
Dr Javier Gonzalez of the Department for Health at the University of Bath explained: “Our results suggest that changing the timing of when you eat in relation to when you exercise can bring about profound and positive changes to your overall health.
“We found that the men in the study who exercised before breakfast burned double the amount of fat than the group who exercised after. Importantly, whilst this didn’t have any effect on weight loss, it did dramatically improve their overall health.
“The group who exercised before breakfast increased their ability to respond to insulin, which is all the more remarkable given that both exercise groups lost a similar amount of weight and both gained a similar amount of fitness. The only difference was the timing of the food intake.”
Over the six-week trial, the scientists found that the muscles from the group who exercised before breakfast were more responsive to insulin compared to the group who exercised after breakfast, in spite of identical training sessions and matched food intake. The muscles from those who exercised before breakfast also showed greater increases in key proteins, specifically those involved in transporting glucose from the bloodstream to the muscles.
For the insulin response to feeding after the 6-week study, remarkably, the group who exercised after breakfast were in fact no better than the control group.
The study was led by Dr Rob Edinburgh as part of his PhD.
Co-author, Dr Gareth Wallis of the University of Birmingham added: “This work suggests that performing exercise in the overnight-fasted state can increase the health benefits of exercise for individuals, without changing the intensity, duration or perception of their effort. We now need to explore the longer-term effects of this type of exercise and whether women benefit in the same way as men.”
The work was funded by The Physiological Society, The Rank Prize Funds, and The Allen Foundation. It is published today (Friday 18 October 2019) in The Journal of Clinical Endocrinology and Metabolism ; doi.org/10.1210/clinem/dgz104.
Andy Dunne [email protected] 01225386319
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Health benefits of physical activity: the evidence
The primary purpose of this narrative review was to evaluate the current literature and to provide further insight into the role physical inactivity plays in the development of chronic disease and premature death. We confirm that there is irrefutable evidence of the effectiveness of regular physical activity in the primary and secondary prevention of several chronic diseases (e.g., cardiovascular disease, diabetes, cancer, hypertension, obesity, depression and osteoporosis) and premature death. We also reveal that the current Health Canada physical activity guidelines are sufficient to elicit health benefits, especially in previously sedentary people. There appears to be a linear relation between physical activity and health status, such that a further increase in physical activity and fitness will lead to additional improvements in health status.
Physical inactivity is a modifiable risk factor for cardiovascular disease and a widening variety of other chronic diseases, including diabetes mellitus, cancer (colon and breast), obesity, hypertension, bone and joint diseases (osteoporosis and osteoarthritis), and depression. 1–14 The prevalence of physical inactivity (among 51% of adult Canadians) is higher than that of all other modifiable risk factors. 15 In this article we review the current evidence relating to physical activity in the primary and secondary prevention of premature death from any cause, cardiovascular disease, diabetes, some cancers and osteoporosis. We also discuss the evidence relating to physical fitness and musculoskeletal fitness and briefly describe the independent effects of frequency and intensity of physical activity. (A glossary of terms related to the topic appears in Appendix 1 ). In a companion paper, to be published in the Mar. 28 issue, we will review how to evaluate the health-related physical fitness and activity levels of patients and will provide exercise recommendations for health.
Several authors have attempted to summarize the evidence in systematic reviews and meta-analyses. These evaluations are often overlapping (reviewing the same evidence). Some of the most commonly cited cohorts have been described in different studies over time as more data accumulate (see Appendix 2, available online at www.cmaj.ca/cgi/content/full/174/6/801/DC1 ). In this review, we searched the literature using the key words “physical activity,” “health,” “health status,” “fitness,” “exercise,” “chronic disease,” “mortality” and disease-specific terms (e.g., “cardiovascular disease,” “cancer,” “diabetes” and “osteoporosis”). Using our best judgment, we selected individual studies that were frequently included in systematic reviews, consensus statements and meta-analyses and considered them as examples of the best evidence available. We also have included important new findings regarding the relation between physical activity and fitness and all-cause and cardiovascular-related mortality.
All-cause and cardiovascular-related death
Since the seminal work of Morris and colleagues in the 1950s 16 , 17 and the early work of Paffenbarger and colleagues in the 1970s, 18 , 19 there have been numerous long-term prospective follow-up studies (mainly involving men but more recently women also) that have assessed the relative risk of death from any cause and from specific diseases (e.g., carciovascular disease) associated with physical inactivity. 6 , 20–26
Both men and women who reported increased levels of physical activity and fitness were found to have reductions in relative risk (by about 20%–35% 27 , 28 ) of death (see Appendix 2, available at www.cmaj.ca/cgi/content/full/174/6/801/DC1 ). For example, in a study involving healthy middle-aged men and women followed up for 8 years, the lowest quintiles of physical fitness, as measured on an exercise treadmill, were associated with an increased risk of death from any cause compared with the top quintile for fitness (relative risk among men 3.4, 95% confidence interval [CI] 2.0 to 5.8, and among women 4.7, 95% CI 2.2 to 9.8). 7
Recent investigations have revealed even greater reductions in the risk of death from any cause and from cardiovascular disease. For instance, being fit or active was associated with a greater than 50% reduction in risk. 29 Furthermore, an increase in energy expenditure from physical activity of 1000 kcal (4200 kJ) per week or an increase in physical fitness of 1 MET (metabolic equivalent) was associated with a mortality benefit of about 20%. Physically inactive middle-aged women (engaging in less than 1 hour of exercise per week) experienced a 52% increase in all-cause mortality, a doubling of cardiovascular-related mortality and a 29% increase in cancer-related mortality compared with physically active women. 30 These relative risks are similar to those for hypertension, hypercholesterolemia and obesity, and they approach those associated with moderate cigarette smoking. Moreover, it appears that people who are fit yet have other risk factors for cardiovascular disease (see Fig. 1 ) may be at lower risk of premature death than people who are sedentary with no risk factors for cardiovascular disease. 31 – 33
Fig. 1: Relative risks of death from any cause among participants with various risk factors (e.g., history of hypertension, chronic obstructive pulmonary disease [COPD], diabetes, smoking, elevated body mass index [BMI ≥ 30] and high total cholesterol level [TC ≥ 5.70 mmol/L) who achieved an exercise capacity of less than 5 METs (metabolic equivalents) or 5–8 METs, as compared with participants whose exercise capacity was more than 8 METs. Error bars represent 95% confidence intervals. Adapted, with permission, from Myers et al 38 ( N Engl J Med 2002;346:793-801). Copyright © 2002 Massachusetts Medical Society. All rights reserved.
An increase in physical fitness will reduce the risk of premature death, and a decrease in physical fitness will increase the risk. 34–37 The effect appears to be graded, 34 , 35 such that even small improvements in physical fitness are associated with a significant reduction in risk ( Fig. 2 ). In one study, 35 participants with the highest levels of physical fitness at baseline and who maintained or improved their physical fitness over a prolonged period had the lowest risk of premature death ( Fig. 2 ). Modest enhancements in physical fitness in previously sedentary people have been associated with large improvements in health status. 38 For instance, in another study, people who went from unfit to fit over a 5-year period had a reduction of 44% in the relative risk of death compared with people who remained unfit. 36
Fig. 2: Relation between changes in physical fitness and changes in mortality over time. Participants were evaluated at baseline (PF1) and again 13 years later (PF2). The ratio of PF2/PF1 × 100 was calculated to evaluate changes in physical fitness over the study period compared with fitness level at baseline. For this figure, participants were grouped according to fitness quartiles (Q1 = least fit, Q4 = most fit) for the baseline evaluation and to quartiles for change in fitness from baseline to 13-year follow-up (Q1 PF2/PF1 = least change, Q4 PF2/PF1 = most change). Adapted, with permission, from Erikssen et al 35 ( Lancet 1998;352:759-62).
A recent systematic review of the literature regarding primary prevention in women 39 revealed that there was a graded inverse relation between physical activity and the risk of cardiovascular-related death, with the most active women having a relative risk of 0.67 (95% CI 0.52 to 0.85) compared with the least active group. These protective effects were seen with as little as 1 hour of walking per week.
In summary, observational studies provide compelling evidence that regular physical activity and a high fitness level are associated with a reduced risk of premature death from any cause and from cardiovascular disease in particular among asymptomatic men and women. Furthermore, a dose– response relation appears to exist, such that people who have the highest levels of physical activity and fitness are at lowest risk of premature death (as discussed later).
Secondary prevention of cardiovascular disease
The benefits of physical activity and fitness extend to patients with established cardiovascular disease. 40 , 41 This is important because, for a long time, rest and physical inactivity had been recommended for patients with heart disease. Unlike studies of primary prevention, many studies of secondary prevention are RCTs (see Appendix 2, available at www.cmaj.ca/cgi/content/full/174/6/801/DC1 ). Several systematic reviews have clearly shown the importance of engaging in regular exercise to attenuate or reverse the disease process in patients with cardiovascular disease. For instance, a systematic review and meta-analysis of 48 clinical trials 5 revealed that, compared with usual care, cardiac rehabilitation significantly reduced the incidence of premature death from any cause and from cardiovascular disease in particular. An energy expenditure of about 1600 kcal (6720 kJ) per week has been found to be effective in halting the progression of coronary artery disease, and an energy expenditure of about 2200 kcal (9240 kJ) per week has been shown to be associated with plaque reduction in patients with heart disease. 42 , 43 Low-intensity exercise training (e.g., exercise at less than 45% of maximum aerobic power) has also been associated with an improvement in health status among patients with cardiovascular disease. 44 However, the minimum training intensity recommended for patients with heart disease is generally 45% of heart rate reserve. 43
In summary, regular physical activity is clearly effective in the secondary prevention of cardiovascular disease and is effective in attenuating the risk of premature death among men and women.
Both aerobic and resistance types of exercise have been shown to be associated with a decreased risk of type 2 diabetes. 9 , 10 , 45–48 In a large prospective study, 46 each increase of 500 kcal (2100 kJ) in energy expenditure per week was associated with a decreased incidence of type 2 diabetes of 6% (relative risk 0.94, 95% CI –0.90 to 0.98)). This benefit was particularly evident among people at high risk of diabetes (i.e., those with a high body mass index), a finding that has been supported by several other investigators. 47 , 49 For instance, among 21 271 male physicians, those who reported weekly physical activity sufficient to cause a sweat had a reduced incidence of type 2 diabetes. 47 Moderately intense levels of physical activity (≥ 5.5 METs for at least 40 minutes per week) and of cardiovascular fitness (> 31 mL oxygen per kilogram per minute) have also been shown to be protective against the development of type 2 diabetes in middle-aged men, 48 with an even greater effect among those at high risk of diabetes.
Several investigators have reported a reduced incidence of type 2 diabetes among high-risk people (e.g., those who are overweight) after lifestyle interventions. 50 , 51 A review of RCTs on the topic 52 concluded that modest weight loss through diet and exercise reduced the incidence of the disease among high-risk people by about 40%–60% over 3–4 years. In one of the RCTs, 53 a lifestyle intervention that included moderate physical activity for at least 150 minutes per week was found to be more effective than metformin alone in reducing the incidence of diabetes. It showed that only 7 people would need to be “treated” with the lifestyle intervention to prevent a single case of diabetes over a 3-year period, compared with 14 people given metformin. 53
In summary, increasing research supports the importance of regular physical activity for the primary prevention of type 2 diabetes. Further research is warranted to uncover the ideal methods (e.g., resistance v. aerobic training) and intensity levels of exercise.
Exercise interventions are also effective in the management of diabetes. One prospective cohort study showed that walking at least 2 hours per week was associated with a reduction in the incidence of premature death of 39%–54% from any cause and of 34%–53% from cardiovascular disease among patients with diabetes. 49 Moreover, walking that led to moderate increases in heart and breathing rates was associated with significant reductions in all-cause mortality (hazard rate ratio 0.57, 95% CI 0.41 to 0.80) and cardiovascular-related mortality (hazard rate ratio 0.69, 95% CI 0.43 to 1.09). 49 In another cohort study, 54 physically inactive men with established type 2 diabetes had a 1.7-fold increased risk of premature death compared with physically active men with type 2 diabetes. This difference has also been observed among people with metabolic syndrome. 55
Several clinical trials have been conducted on the topic. 56 – 63 Both aerobic and resistance training have been shown to be of benefit for the control of diabetes; however, resistance training may have greater benefits for glycemic control than aerobic training may have. 58 A meta-analysis of 14 controlled trials (11 randomized) revealed that exercise interventions resulted in a small but clinically and statistically significant reduction in glycosylated hemoglobin (0.66%) compared with no exercise intervention; 64 in most of the trials, participants in both the exercise and control groups were treated concurrently with oral hypoglycemic agents. This level of change is similar to that observed in studies comparing intensive glucose-lowering therapy with conventional treatments, a change that is known to be associated with a 42% reduction in diabetes-related mortality. 64
In summary, exercise interventions for patients with diabetes are beneficial in improving glucose homeostasis. Prospective studies with adequate follow-up show a strong association between exercise and reduced rates of death from any cause and from diabetes in particular. Future research will need to concentrate on examining the effects of dose (intensity and frequency of exercise).
Several seminal reviews have been published regarding the relation between cancer and routine physical activity 65–67 (see Appendix 2, available at www.cmaj.ca/cgi/content/full/174/6/801/DC1 ). Of the available literature (including over 100 epidemiologic studies 65 ), it appears that routine physical activity, whether as part of a job or as a leisure activity, is associated with reductions in the incidence of specific cancers, in particular colon and breast cancer. 67–71 A systematic review of epidemiologic studies revealed that moderate physical activity (> 4.5 METs [equivalent to mowing the lawn]) was associated with a greater protective effect than activities of less intensity. 65 Physically active men and women exhibited a 30%–40% reduction in the relative risk of colon cancer, and physically active women a 20%–30% reduction in the relative risk of breast cancer compared with their inactive counterparts. 65
In summary, there is compelling evidence that routine physical activity is associated with reductions in the incidence of specific cancers, in particular breast and colon cancer.
There is a paucity of information regarding the effectiveness of physical activity in preventing death from cancer or from any cause in patients with cancer. An early (5.5-year) follow-up study involving women with breast cancer revealed little association between total recreational physical activity and the risk of death from breast cancer; 72 however, the study had some important limitations. 73 Two recent follow-up studies involving cancer patients (breast and colon cancer) revealed that increased self-reported physical activity was associated with a decreased recurrence of cancer and risk of death from cancer. 74 , 75 One investigation 74 revealed a reduction of 26%–40% in the relative risk of cancer-related death and recurrence of breast cancer among the most active women compared with the least active. Other studies have shown similar associations. 75 , 76 There are ongoing efforts to try to understand the mechanism of this survival effect, including the effects of exercise on the effectiveness of chemotherapy. 77 Regular physical activity has also been shown to be associated with an improvement in overall quality of life and health status of patients with cancer. 78 – 82
In summary, regular physical activity appears to confer a health benefit to patients with established cancer. However, further research is warranted to examine its role in the secondary prevention of cancer. In particular, large RCTs evaluating the effectiveness of an exercise intervention are required to fully elucidate the importance of regular physical activity for the health status of patients with cancer.
Weight-bearing exercise, especially resistance exercise, appears to have the greatest effects on bone mineral density. In one review, 10 several cross-sectional reports revealed that people who did resistance training had increased bone mineral density compared with those who did not do such training. Furthermore, athletes who engaged in high-impact sports tended to have increased bone mineral density compared with athletes who engaged in low-impact sports. 10
Numerous longitudinal studies have examined the effects of exercise training on bone health in children, adolescents, and young, middle-aged and older adults (see relevant reviews 83–86 and Appendix 2, available at www.cmaj.ca/cgi/content/full/174/6/801/DC1 ). Although the numbers of studies and total participants examined are relatively small compared with those in the cardiovascular literature, there is compelling evidence that routine physical activity, especially weight-bearing and impact exercise, prevents bone loss associated with aging. In a meta-analysis of RCTs, exercise training programs were found to prevent or reverse almost 1% of bone loss per year in the lumbar spine and femoral neck in both pre-and postmenopausal women. 87 Exercise training appears to significantly reduce the risk and number of falls. 88–92
The risk and incidence of fractures is also reduced among active people. 93–95 Among 3262 healthy men (mean age 44 years) followed for 21 years, 96 intense physical activity at baseline was associated with a reduced incidence of hip fracture (hazard ratio 0.38, 95% CI 0.16 to 0.91). This observation supports findings from an earlier investigation in which fracture rates were lower among people who performed more weight-bearing activities than among sedentary people. 97
In summary, routine physical activity appears to be important in preventing loss of bone mineral density and osteoporosis, particularly in postmenopausal women. The benefits clearly outweigh the potential risks, particularly in older people.
Preliminary evidence from an RCT indicates that exercise training is effective in improving bone density in older women (75–85 years of age) with low bone mineral density. 98 In this 6-month RCT, 98 women were randomly assigned to participate in resistance training ( n = 32), agility training ( n = 34) or stretching (sham exercise, n = 32). Agility training resulted in a significant increase in cortical bone density by 0.5% (standard error of the mean [SEM] 0.2%) at the tibial shaft, and resistance training resulted in a significant increase in cortical bone density by 1.4% (SEM 0.6%) at the radial shaft; the stretching group experienced losses in cortical bone density. 98 Furthermore, a study involving early postmenopausal osteopenic women revealed that a 2-year intensive training program was effective in attenuating the rate of bone loss. 99
In summary, preliminary evidence indicates that regular physical activity is an effective secondary preventive strategy for the maintenance of bone health and the fight against osteoporosis.
Physical activity or physical fitness?
Physical fitness refers to a physiologic state of well-being that allows one to meet the demands of daily living or that provides the basis for sport performance, or both. Health-related physical fitness involves the components of physical fitness related to health status, including cardiovascular fitness, musculoskeletal fitness, body composition and metabolism. In large epidemiologic investigations, physical activity and physical fitness are often used interchangeably, with fitness commonly being treated as a more accurate (albeit indirect) measure of physical activity than self-report. 100
Physical fitness appears to be similar to physical activity in its relation to morbidity and mortality 2 , 34 but is more strongly predictive of health outcomes than physical activity. 6 , 29 , 100 Most analyses have shown a reduction of at least 50% in mortality among highly fit people compared with low-fit people (see Appendix 2, available at www.cmaj.ca/cgi/content/full/174/6/801/DC1 ). 29
Nonetheless, both physical activity and fitness are strong predictors of risk of death. 29 To obtain accurate estimates of physical activity, many fitness consultants rely on primary (criterion and “gold”) standards for the measurement of energy expenditure, such as direct observation of movement or, in the laboratory, the doubly labelled water technique or indirect calorimetry. 101 On a practical basis, however, measures of physical activity and energy expenditure are obtained by using heart rate monitors and motion sensors (pedometers and accelerometers). These devices will be briefly reviewed in the companion article in the Mar. 28 issue.
The assessment of physical fitness is often not feasible or practical in large population-based investigations. Fortunately such studies have consistently shown an inverse gradient of health risk across self-reported physical activity groups. From a public health perspective, Blair and colleagues 6 have argued that it is preferable to encourage people to become more physically active rather than to become physically fit, since, as they stated, sedentary people will likely achieve the latter if they do the former.
Musculoskeletal fitness: a paradigm shift
Improvements in indicators of health status can occur as a result of increasing physical activity levels in the absence of changes in aerobic fitness. This is particularly evident in elderly populations, where regular physical activity can lead to reductions in risk factors for chronic disease and disability 3 , 9 , 10 without markedly changing traditional physiologic performance markers (e.g., cardiac output and oxidative potential). 3 Furthermore, routine physical activity can improve musculoskeletal fitness. 9 , 10 There is increasing evidence that enhanced musculoskeletal fitness is associated with an improvement in overall health status and a reduction in the risk of chronic disease and disability. 9 , 10 This research has led to a shift in focus in research related to the health benefits of activities that tax the musculoskeletal system.
Musculoskeletal fitness appears to be particularly important for elderly people and their ability to maintain functional independence. In fact, many activities of daily living do not require a large aerobic output but depend on one or more of the musculoskeletal fitness components. 9 , 10 As previously stated, 10 “Many healthy elderly people may be at or near the functional threshold for dependence, wherein they are in jeopardy of losing the capacity to carry out the activities of daily living. With further worsening of musculoskeletal fitness, an individual may lose the capacity to perform daily activities, such as getting out of a chair or climbing stairs.” This represents a cycle of decline, where reduced musculoskeletal fitness leads to inactivity and further dependence. As illustrated in Fig. 3 , improvements in musculoskeletal function have an enormous potential for delaying or eliminating the onset of disability, dependence and chronic disease. 9 , 10 For instance, previous longitudinal investigations have revealed that people with high levels of muscular strength have fewer functional limitations 102 , 103 and lower incidences of chronic diseases such as diabetes, stroke, arthritis, coronary artery disease and pulmonary disorders. 103
Fig. 3: Theoretical relation between musculoskeletal fitness and independent living across a person's lifespan. As a person ages, his or her musculoskeletal fitness (i.e., muscular strength, muscular endurance, muscular power or flexibility) declines, such that a small impairment may result in disability. Many elderly people currently live near or below the functional threshold for dependence. High levels of (or improvements in) musculoskeletal fitness will enhance the capacity to meet the demands of everyday life and allow a person to maintain functional independence for a greater period. 9 , 10
Two recent systematic reviews 9 , 10 have revealed that enhanced musculoskeletal fitness is positively associated with functional independence, mobility, glucose homeostasis, bone health, psychological well-being and overall quality of life and is negatively associated with the risk of falls, illness and premature death. Interventions that improve musculoskeletal fitness appear to be particularly important for improving the health status of frail elderly people (who have a low musculoskeletal reserve). 9 , 10 This research has revealed clearly the importance of engaging in activities that tax the musculoskeletal system and is supported by findings from a recent epidemiologic investigation. 104 This evidence provides direct support for the recent recommendation that resistance training and flexibility exercises be performed at least twice a week to maintain functional status, promote lifelong physical activity and enhance overall quality of life. 3 , 105
How much physical activity is enough?
It is apparent that physical activity is essential in the prevention of chronic disease and premature death. 14 However, doubt remains over the optimal “volume” (frequency, duration and intensity of exercise) and the minimum volume for health benefits, in particular the effects of intensity (e.g., moderate v. vigorous) on health status. There is evidence that intensity of physical activity is inversely and linearly associated with mortality. 14 Early work by Paffenbarger and associates 106 revealed that regular physical activity (expending > 2000 kcal [8400 kJ] per week) was associated with an average increase in life expectancy of 1 to 2 years by the age of 80 and that the benefits were linear even at lower levels of energy expenditure. Subsequent studies have shown that an average energy expenditure of about 1000 kcal (4200 kJ) per week is associated with a 20%–30% reduction in all-cause mortality. 14 , 106 , 107 Currently, most health and fitness organizations and professionals advocate a minimum volume of exercise that expends 1000 kcal (4200 kJ) per week and acknowledge the added benefits of higher energy expenditures.
Recently, investigators have postulated that even lower levels of weekly energy expenditure may be associated with health benefits. 107–109 A volume of exercise that is about half of what is currently recommended may be sufficient, 14 particularly for people who are extremely deconditioned or are frail and elderly. 6 Future research is required to determine whether expending as little as 500 kcal (2100 kJ) per week offers health benefits. If so, then previously sedentary people may be more likely to engage in physical activity and maintain an active lifestyle.
The dose–response relation between physical activity and health status outlined above generally relates to cardiovascular disease and premature death from any cause. However, the same may hold true for other activity-associated health benefits. For instance, as mentioned earlier, moderately intense levels of exercise (≥ 5.5 METs for at least 40 minutes per week) and of cardiovascular fitness (> 31 mL oxygen per kilogram per minute) are effective preventive strategies against type 2 diabetes. 48 In patients with type 2 diabetes, walking more than 2 hours per week has also been shown to reduce the risk of premature death. 49
With respect to cancer, a review of the literature revealed that moderate physical activity (> 4.5 METs) for about 30–60 minutes per day had a greater protective effect against colon and breast cancer than activities of low intensity. 67 The greatest benefit for reducing the incidence of breast cancer was observed among women who engaged in 7 or more hours of moderate-to-vigorous activity per week. 110 Among patients with established cancer, physical activity equivalent to walking 1 or more hours per week was associated with improved survival compared with no exercise. 74 The greatest benefit was observed among cancer survivors who performed exercise equivalent to 3–5 hours per week at an average pace. 74
With respect to osteoporosis, the dose–response relation of physical activity is less clear. However, osteogenic adaptations appear to be load-dependent and site-specific. 9 , 10 , 111 Accordingly, physical activities that require impact or significant loading are therefore advocated for optimal bone health. Running distances of up to 15–20 miles (24–32 km) per week has been associated with the accrual or maintenance of bone mineral density, but longer distances may be associated with reduced bone mineral density. 112
How does physical activity and fitness lead to improved health outcomes?
Several biological mechanisms may be responsible for the reduction in the risk of chronic disease and premature death associated with routine physical activity. For instance, routine physical activity has been shown to improve body composition (e.g., through reduced abdominal adiposity and improved weight control), 9 , 10 , 113–116 enhance lipid lipoprotein profiles (e.g., through reduced triglyceride levels, increased high-density lipoprotein [HDL] cholesterol levels and decreased low-density lipoprotein [LDL]-to-HDL ratios), 9 , 10 , 117–123 improve glucose homeostasis and insulin sensitivity, 3 , 9 , 10 , 124–126 reduce blood pressure, 127–130 improve autonomic tone, 131 , 132 reduce systemic inflammation; 133 decrease blood coagulation, 134 , 135 improve coronary blood flow, 136 augment cardiac function 137 , 138 and enhance endothelial function. 139–142 Chronic inflammation, as indicated by elevated circulating levels of inflammatory mediators such as C-reactive protein, has been shown to be strongly associated with most of the chronic diseases whose prevention has benefited from exercise. Recent RCTs have shown that exercise training may cause marked reductions in C-reactive protein levels. 143 Each of these factors may explain directly or indirectly the reduced incidence of chronic disease and premature death among people who engage in routine physical activity.
Routine physical activity is also associated with improved psychological well-being (e.g., through reduced stress, anxiety and depression 9 , 10 , 144 ). Psychological well-being is particularly important for the prevention and management of cardiovascular disease, but it also has important implications for the prevention and management of other chronic diseases such as diabetes, osteoporosis, hypertension, obesity, cancer and depression.
Changes in endothelial function may be a particularly important adaptation to routine physical activity. Endothelial dysfunction has been observed with aging, smoking and multiple chronic disease states, including coronary artery disease, congestive heart failure, stroke, type 2 diabetes, hypertension, hypercholesterolemia and obesity. 116 Regular aerobic activity has been found to improve vascular function in adults independent of changes in other risk factors 142 , 145 and has been said to result in a shear-stress–mediated improvement in endothelial function, 116 which confers a health benefit to a number of disease states. 146
Although most research into the mechanisms of how physical activity and fitness improve health outcomes has dealt with the relation between cardiovascular disease and physical activity, researchers have also evaluated the primary mechanisms responsible for decreases in the risk and severity of individual disease states. In fact, despite the adaptations that are of global benefit for multiple disease states, physical activity also results in specific adaptations that affect individual disease states. For instance, in type 2 diabetes, adaptations that affect glucose homeostasis are of great importance. As reviewed by Ivy, 147 a series of changes (independent of changes in body mass 64 ) occur as a result of regular physical activity, including increased glycogen synthase 148 and hexokinase activity, 149 increased GLUT-4 protein and mRNA expression, 148 , 150 and improved muscle capillary density (resulting in improved glucose delivery to the muscle). 149 A series of mechanisms may explain the 46% reduction in cancer rates observed with regular physical activity, 66 including reductions in fat stores, 66 increased energy expenditure offsetting a high-fat diet, 66 activity-related changes in sex hormone levels, immune function, insulin and insulin-like growth factors, free-radical generation, 151 and direct effects on the tumour. 151
The majority of proposed mechanisms have been discussed in the context of chronic adaptations brought about by routine physical activity. However, researchers have recently examined the importance of acute changes in risk factors for chronic disease. 152 An excellent review of the topic by Thompson and colleagues revealed that acute, dynamic exercise may result in transient changes in the form of reductions in triglyceride levels, increases in HDL cholesterol level, decreases in blood pressure (for 12–16 hours), reductions in insulin resistance and improvements in glucose control. 152 These acute changes indicate the important role individual exercise sessions have on health status.
There is incontrovertible evidence that regular physical activity contributes to the primary and secondary prevention of several chronic diseases and is associated with a reduced risk of premature death. There appears to be a graded linear relation between the volume of physical activity and health status, such that the most physically active people are at the lowest risk. However, the greatest improvements in health status are seen when people who are least fit become physically active. The current activity guidelines promoted by Health Canada appear to be sufficient to reduce health risk. People who engage in exercise at levels above those recommended in the guidelines are likely to gain further health benefits. Health promotion programs should target people of all ages, since the risk of chronic disease starts in childhood and increases with age.
In the next issue, we will review how to evaluate the health-related physical fitness and activity levels of patients and will provide exercise recommendations for health.
This research was supported by the Michael Smith Foundation for Health Research, the Canadian Institutes of Health Research, the Canada Foundation for Innovation and the BC Knowledge Development Fund.
This article has been peer reviewed.
Contributors: Darren Warburton was responsible for the conception of the review and the writing of the manuscript. Shannon Bredin provided assistance with the writing of the manuscript and background research. Crystal Whitney Nicol provided assistance with background research. All of the authors critically reviewed the article for intellectual content and approved the final version.
Competing interests: None declared.
Correspondence to: Dr. Darren E.R. Warburton, Cardiovascular Physiology and Rehabilitation Laboratory, University of British Columbia, Unit II, Osborne Centre, 6108 Thunderbird Blvd., Vancouver BC V6T 1Z3; fax 604 822-9451; [email protected]
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Mind & Mood
More evidence that exercise can boost mood
Running for 15 minutes a day or walking for an hour reduces the risk of major depression, according to a recent study..
It may be possible to outrun depression, according to a study published online January 23 by JAMA Psychiatry .
"We saw a 26% decrease in odds for becoming depressed for each major increase in objectively measured physical activity," says study author Karmel Choi, a clinical and research fellow at the Harvard T.H. Chan School of Public Health. "This increase in physical activity is what you might see on your activity tracker if you replaced 15 minutes of sitting with 15 minutes of running, or one hour of sitting with one hour of moderate activity like brisk walking."
Cause or effect?
This isn't the first study to show that exercise may benefit mood. But until now it's largely been something of a chicken-and-egg discussion — which came first?
"We hear a lot that exercise and mood are connected. What we don't know for sure is whether being physically active can improve emotional well-being, or if we simply move less when we feel sad or depressed," says Choi.
This study aimed to find out. "We wanted to see if there might be a causal connection, in either direction, between physical activity and depression," says Choi. "Does physical activity protect against depression? Or does depression simply reduce physical activity? Our study allowed us to untangle those questions in a powerful new way using genetic data."
To do this, the study applied a technique known as Mendelian randomization, using data from two large genetic databases that included hundreds of thousands of people. Having access to genetic data allowed researchers to use genetic variations between people as a kind of natural experiment to better see how exercise affects depression, and vice versa, says Choi. What they found is that exercise was able to independently reduce the risk for depression.
People who moved more, they found, had a significantly lower risk for major depressive disorder — but only when the exercise was measured objectively using a tracking device, not when people self-reported how much exercise they performed.
Identifying types of movement
People are not always accurate when it comes to assessing or keeping track of how much they're truly moving. "We see in the research literature that objective and self-reported measures of physical activity don't always line up," says Choi. "Objective measures offer unique perks because they don't rely on people's memory and are not affected by people wanting to present themselves in a certain way."
In addition, the tracking device was better at assessing overall movement. It didn't just give people credit for formal exercise. It also measured how much they moved throughout the day during ordinary activities.
"This can include taking the stairs or walking to the store or putting away laundry, things that people may not recognize as being active but may add up," says Choi. This is good news, because it means you don't need to be huffing and puffing on a stair machine to reduce your risk of depression.
Little movements add up
"What our study would say is that any kind of movement can add up to keep depression at bay. I think that's why our study findings were especially appealing. It didn't say you have to run a marathon, do hours of aerobics, or be a CrossFit master just to see benefits on depression," says Choi.
So, the message is this: If you do love a good, hearty gym workout, keep going. But if you don't, just getting off the couch and moving for a little while can help. Ideally, to prevent depression you should do at least 15 minutes a day of higher-intensity exercise, such as running, or at least an hour of lower-intensity exercise, such as walking or housework.
"Intentionally moving your body in more gentle ways throughout the day — like walking, stretching, taking the stairs, doing the dishes — can still add up in good ways for your mood. I think that's an encouraging message," says Choi.
Image: © kali9/Getty Images
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The Benefits of Exercise for Children’s Mental Health
Even light physical activity among adolescents was linked to better mental health as they got older, new research shows.
By Perri Klass, M.D.
Recent research on the link between physical activity and depression risk in adults has suggested that exercise may offset the genetic tendency toward depression. Adults with genetic risks who exercised regularly were no more likely to develop depression than those without the genetic propensity.
There’s good evidence that this same association holds in adolescents, a group with a generally high risk of depression, and with concerningly high suicide rates. But adolescence is also a time when physical activity often becomes less common, especially among girls .
The World Health Organization recommendation is for an hour of moderate to vigorous exercise every day for adolescents, in addition to whatever they do in school — that means activity that gets you sweating and breathing hard. But many adolescents don’t exercise anywhere near that much.
So people who study adolescent mental health and suicide prevention are interested in the possible protective effects of more limited exercise or more moderate physical activity — and also, of course, in the question of how to help adolescents get moving.
A prospective study published in the March issue of the journal The Lancet Psychiatry found that even light activity — and a corresponding decrease in the amount of time that kids spent being sedentary — was linked to better mental health as they got older.
The researchers looked at the activity of adolescents at the ages of 12, 14 and 16, who were then assessed for depression at around 18. The participants wore devices called accelerometers, which continuously measured their activity during the day.
The first author on the new study, Aaron Kandola, a Ph.D. candidate in physical activity and mental health at University College London, said that many of the older studies had relied on memory, asking people what they had done in their leisure time. While this captures exercise and other moderate activity, he said, it misses light activity, which actually makes up the bulk of many people’s movement during the day — walking at a casual pace, shopping, playing an instrument, doing chores around the house.
The study found that total physical activity dropped between ages 12 and 16, mostly because of decreases in that light activity, and sedentary behavior increased. And the activity levels when kids were younger were linked to their mental health later on; the depression scores at 18 were lower for every additional 60 minutes per day of light activity at 12, 14 and 16, and higher for every additional sedentary hour.
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Mr. Kandola said that by age 16, young people in the study were spending an average of close to nine hours a day on sedentary activity, and that it would be hard to decrease that behavior significantly through exercise, because it would require lots of exercise to significantly reduce that amount of sedentary time. If the goal is to reduce sedentary time significantly (say, by two hours a day), it might be useful to build in more light activity — for example, by reshaping the school environment, he said.
“We have this time at school where we have put out an agenda of sedentary behavior,” he said, citing the emphasis on sitting down, with rare breaks. “It’s time for reforms to target the school system.” He suggested that activity breaks be scheduled regularly in schools , and that schools try standing desks, which have been successful in workplaces.
Xihe Zhu, an associate professor of human movement science at Old Dominion University in Norfolk, Va., said that research shows that “some exercise is going to be much better than no exercise at all.” Dr. Zhu was the first author on a 2019 study of 35,000 children and adolescents from 6 to 17 in the United States, which found that those who reported no exercise were twice as likely to have mental health problems, particularly related to anxiety and depression, compared with those who met the exercise guidelines.
Even if children exercised only one to three days a week, he said, there was a strong correlation with lower rates of anxiety and depression — and there was no significant difference between them and those who exercised four to six days a week.
Good sleep duration and extracurricular activities were also associated with better mental health. In fact, physical activity may improve sleep quality, which is closely linked to mental health.
Elaine McMahon, a research fellow at the National Suicide Research Foundation and the School of Public Health, University College Cork in Ireland, was the lead author on a 2017 study coming out of a large research project on European adolescents.
They studied more than 11,000 13- to 15-year-olds in 10 countries, and found that only 13.6 percent of them met the recommended guidelines of 60 minutes of moderate to vigorous exercise a day.
There was a clear association between more frequent physical activity and lower levels of depression and anxiety, but the most significant difference was between the least active group (active for 60 minutes or more on zero to three of the past 14 days) and the somewhat active group (four to seven of the past 14 days). The most active group (eight to 14 of the past 14 days) had the highest levels of well-being and the lowest levels of depression and anxiety, though within that group, daily activity conferred no special benefit.
The study also found that being on a sports team was associated with an extra improvement in mental health, beyond what was associated with the physical activity — and it was particularly strong for girls.
There were striking differences among the 10 countries. In Slovenia, 66.9 percent of the boys and 49.7 percent of the girls were in the most active group; in Italy it was only 27.8 percent of the boys and 9.6 percent of the girls.
“What’s going so right in some countries in terms of keeping girls active through adolescence?” Dr. McMahon asked. “Is it about offering a larger variety of activities, or school schedule, or a culture of outdoor activity?” The variety of activities available matters, she said, and so does building sports into the curriculum and making sure there is free time in an adolescent’s week, and encouraging them to walk or bike to school.
The cross-sectional studies that show an association between exercise and better mental health cannot actually show causality, and being depressed or otherwise affected by mental health problems might stop a person from exercising. “When you look at populations with mental health issues, they typically have low physical activity or exercise,” Dr. Zhu said. In adults, those populations also typically have high levels of obesity and cardiovascular health problems, he said.
But recent prospective studies, including this new one looking at adolescents, build on what we already know to suggest that there is a strong relationship in the other direction: Regular exercise lowers your risk of developing depression. A 2019 review by Mr. Kandola and his colleagues cited a number of possible ways exercise may affect depression, including biological mechanisms like stimulation of neurological pathways and processes, and reducing inflammation, but also that “exercise promotes self-esteem, social support and self-efficacy.”
So the message is that exercise is good, activity is important, but you’ll start seeing benefits long before you get to that solid hour a day. “Moderate activity of any kind, getting out and doing something, is associated with improvements, lower levels of depressive symptoms, lower levels of anxiety, better well-being,” Dr. McMahon said.
Exercise and mental health
Actions for this page.
- People who exercise regularly have better mental health and emotional wellbeing, and lower rates of mental illness.
- Exercise is important for people with mental illness – it not only boosts our mood, concentration and alertness, but improves our cardiovascular and overall physical health.
- Exercise doesn’t have to be strenuous, structured or take a long time to have benefits.
- Any exercise is better than none, but experts recommend adults should be active most days, aiming for a total of 2.5-5 hours of moderate physical activity, or 1.25-2.5 hours of vigorous physical activity per week.
On this page
Why does exercise make us feel better, mentally, exercising for your mental health, how to get started with exercise, exercise outdoors, how to be more active every day, where to get help.
We all know how important exercise is for keeping us physically healthy. But did you know that exercise can also help keep you mentally healthy?
Research shows that people who exercise regularly have better mental health and emotional wellbeing, and lower rates of mental illness .
Taking up exercise seems to reduce the risk of developing mental illness. It also seems to help in treating some mental health conditions, like depression and anxiety . For example, for mild-moderate depression, research suggests physical activity can be as effective as antidepressants or psychological treatments like cognitive behavioural therapy . Exercise can also a valuable addition to other treatment options.
Often, people who exercise regularly do it simply because it makes them feel good. Exercise can boost your mood, concentration and alertness. It can even help give you a positive outlook on life.
The link between exercise and mental health is complicated. Inactivity can be both a cause and a consequence of mental illness, for example. But there are lots of ways that exercise can benefit your mental health, such as:
- The levels of chemicals in the brain, such as serotonin, stress hormones and endorphins, change when you exercise.
- Regular exercise can help you sleep better. And good sleep helps you manage your mood .
- Exercise can improve your sense of control, coping ability and self-esteem. People who exercise regularly often report how good achieving a goal makes them feel.
- Exercise can distract you from negative thoughts and provide opportunities to try new experiences.
- It offers an opportunity to socialise and get social support if you exercise with others.
- Exercise increases your energy levels.
- Physical activity can be an outlet for your frustrations.
- Exercise can reduce skeletal muscle tension, which helps you feel more relaxed.
The physical benefits of exercise are also important for people with mental illness. It improves your cardiovascular health and overall physical health. This is important because people with mental health issues are at a higher risk of suffering from chronic physical conditions such as heart disease , diabetes , arthritis and asthma .
If regular exercise is not already a part of your routine, you might be wondering how much you need to do to give your mental health a boost.
The really good news is exercise doesn’t have to be strenuous or take a long time. Studies show low or moderate intensity exercise is enough to make a difference in terms of your mood and thinking patterns.
Australia’s physical activity and sedentary guidelines External Link recommend adults should be active most days, aiming for a total of 2.5-5 hours of moderate physical activity per week, such as a brisk walk or swimming. Alternatively, they recommend getting 1.25-2.5 hours of vigorous physical activity per week - such as jogging, fast cycling, or a team sport. Or, you can combine both moderate and vigorous activities.
However, any exercise is better than none. Going for a leisurely walk, or activities like stretching and yoga, can also have huge benefits on your mind and body. Even doing housework like sweeping, mopping, or vacuuming can give you a mild work out.
It can be intimidating to start exercising if you haven’t done it in a while, but a plan can help you start and stick with it.
Your new exercise plan has a better chance of success if you:
- see your GP or an accredited exercise physiologist External Link before you start, and regularly as you continue your exercise plan
- choose an activity you like, or have enjoyed in the past, that suits your fitness levels and abilities
- start small – build up your activity gradually. Ideally, vary your activities so you don’t get bored
- write your plan in your diary or on your calendar, so it’s part of your schedule
- regularly revisit your exercise plans, and try something different if it’s not working out for you.
For even greater benefits, try exercising outdoors.
Some recent studies have found people report a higher level of vitality, enthusiasm, pleasure and self-esteem, and a lower level of tension, depression and fatigue, after they have walked outside. People who exercise outside also say they are more likely to exercise again than those who stay indoors.
And, people who exercise outside do it more often, and for longer, than those who work out indoors.
Make exercise part of your everyday activity. Try walking or cycling instead of using the car. Get off a tram, train or bus a stop earlier and walk the rest of the way. Or spend some time walking your kids to school. Get active around the house by doing some gardening, washing the car or cleaning the windows.
Australia’s physical activity and sedentary guidelines External Link can give you more information. The important thing to remember is to try to move more and sit less every day.
- Your GP (doctor)
- Registered Exercise Professional External Link
- Exercise Physiologist
- Physical activity and exercise guidelines for all Australian External Link , Department of Health, Australian Government.
- Physical activity and exercise External Link , Department of Health, Australian Government.
- Stanton R, Rosenbaum S, Kalucy M et al. 2014, ‘ A call to action: exercise as treatment for patients with mental illness External Link ’, Australian Journal of Primary Health, vol. 21, no. 2, pp. 120–125.
- Physical activity External Link , Department of Health, Victorian Government.
- Kvam et al. 2016, Exercise as a treatment for depression: A meta-analysis External Link .
- Anderson & Shivakumar, 2013, Effects of exercise and physical activity on anxiety External Link .
- Cramer et al. 2013, Yoga for depression: a systematic review and meta-analysis External Link .
- Morgan et al. 2013, Exercise and mental health: An Exercise and Sports Science Australia Commissioned Review External Link .
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New Report: Exercise Plays Key Role in Mental Health & Well-being
Current evidence suggests physical activity and exercise benefit mental health. In June 2021, the John W. Brick Foundation released their Move Your Mental Health Report, a scoping review of studies conducted over the last thirty years. This article outlines the key findings of the report and what this data means for fitness industry professionals.
Alexandra Black Larcom
- July 14, 2021
As the world continues to slowly emerge from the COVID-19 pandemic, the long-term impacts of the last 18 months on physical and mental health are yet to be determined. Some mental health experts fear a “tsunami” of mental health issues to emerge in the near future. Investment in strategies to improve and address mental health has never been more prescient.
There has long been data to suggest physical activity and exercise benefit mental health. In June 2021, the John W. Brick Foundation released their Move Your Mental Health Report , which provides a scoping review of over 1,000 studies conducted over the last thirty years. The research cast a wide net, including studies on any variety of physical activity, exercise, or movement type and any mental health outcome published between 1990 and 2020.
The findings were overwhelmingly positive. Out of 1,158 studies examined, 89% found a statistically significant, positive association between physical activity or exercise and mental health. The top three exercise types linked to mental health benefits were:
general physical activity (a broad category representing any movement),
cardiovascular/aerobic physical activity, and
When considering solely randomized controlled trials (RCTs)—often thought of as the gold standard and most rigorous study type—87% found statistically significant positive associations between physical activity or exercise and mental health.
Exercise and Mental Health
This review found statistically significant and beneficial links between several types of physical activity and depression, general anxiety, mood, general mental health, quality of life, stress, and well-being.
The strongest associations across the board were for depression. A review cited in the report and published in the Journal of the American Medical Association, including 39 trials, found that exercise was associated with reduced depression symptoms when compared with no treatment and placebo and active control groups. Additional studies found that the effects of exercise were not different from psychotherapy or antidepressants.
Research also suggests exercise is beneficial for anxiety. Meta-analyses of studies have shown that exercise is more effective in treating anxiety than control group settings. Exercise improved anxiety symptoms in people with an anxiety diagnosis or other stress-related disorder and those with “clinically raised” anxiety. A growing body of evidence suggests physical activity can provide immediate anxiety relief following a session. The evidence shows that exercise can be a long-term solution and also a potential immediate coping mechanism for people with anxiety.
The evidence thus far suggests an effective exercise regimen for depression and anxiety includes both aerobic and resistance training across four to five 30-45 minute sessions each week. Exercise should also be supervised by a trained fitness professional and be mindful of participants’ enjoyment, community, and culture to maximize adherence. People with anxiety also benefit from adding more mindful forms of exercise like yoga, Tai Chi, and Qigong one or two times per week.
Exercise and Mental Illness
While exercise cannot cure mental illness, it can still provide important benefits to overall well-being.
For example, the report highlights evidence suggesting aerobic exercise can lower psychiatric symptoms and improve cognition in people with schizophrenia type disorders. A study including 39 trials found that physical activity interventions had a significant effect on lower depression symptoms and schizophrenia symptoms. Interventions also improved quality of life in people with mental illness.
The report also points to a 19 study meta-analysis, which found that yoga was better for depressive symptoms in contrast to no treatment or treatment as usual for people with:
alcohol use, and
In this analysis, the authors noted a link between a higher frequency of yoga and a greater reduction in symptoms.
Less evidence was available for serious mental illnesses like bipolar disorder and schizophrenia. Although, research suggests that physical activity is more beneficial for controlling “negative” symptoms—such as withdrawal and apathy—than for “positive” symptoms—as in hallucinations or confused thoughts. Another added benefit of physical activity for people with serious mental illness is its role in preventing and managing cardiometabolic diseases, which can often accompany these illnesses, increase disease risk, and reduce longevity.
According to the report, the benefits of exercise and physical activity for mental health are most apparent when:
intensity is moderate to vigorous,
it occurs several times per week,
engaging in a combination of aerobic and resistance training, and
it includes mindfulness-based activities like yoga, Tai Chi, and Qigong.
It’s important to remember that more is not always best. The evidence suggests a U-shaped curve, with peak benefits at a regimen of moderate-vigorous exercise three to five times weekly. In alignment with global and U.S. physical activity guidelines recommendations, combining cardiovascular training with resistance or muscular strengthening exercise was more beneficial than either one alone.
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