Any physical activity improves CV fitness; timing may play role
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The timing of moderate to vigorous physical activity bouts may improve cardiorespiratory fitness for adults with type 2 diabetes and obesity, especially for men, according to an analysis of Look AHEAD study data.
“In our study, we find that performing regular physical activity is better for cardiovascular fitness than not being active,” Roeland J.W. Middelbeek, MD, MSc, staff physician, research associate and instructor in medicine at Harvard Medical School and Joslin Diabetes Center, told Healio. “What we also found is that the timing of physical activity — which includes exercise, but also housework and physical labor — and associations with fitness and risk for heart disease in men vary by time of day, independent of total amount performed.”
Exercise timing, intensity
Middelbeek and colleagues analyzed data from 2,035 participants (57% women) of Look AHEAD, a study examining the effect of intensive lifestyle intervention on the primary and secondary prevention of CVD among adults with type 2 diabetes and overweight or obesity. Eligible adults, recruited between August 2001 and April 2004, were aged 45 to 75 years and were randomly assigned to intensive lifestyle intervention or a control group that included brief diet and exercise education sessions and social support. Participants wore a hip-mounted accelerometer for 7 days at baseline.
Researchers assessed bout-related moderate to vigorous intensity physical activity, defined as any activity that met at least three metabolic equivalents of task [MET] per minute for at least 10 minutes, as well as cardiorespiratory fitness via a maximal graded exercise test. Participants were categorized into six groups based on the time of day for completing the majority of exercise bouts: at least 50% of bout-related physical activity performed during the same time window each week (morning [n = 280], midday [n = 235], afternoon [n = 214] or evening [n = 246]), less than 50% of bout-related physical activity performed in any time category (mixed; reference group; n = 436), and 1 day or fewer per week performing bout-related physical activity (inactive group; n = 624). Primary outcome was cardiorespiratory fitness; secondary outcome was 4-year Framingham Risk Score (FRS).
Researchers used linear regression models to determine associations between outcomes and timing of bout-related physical activity.
Compared with adults in the mixed exercise timing group, the inactive group had lower cardiorespiratory fitness (mean beta coefficient, –0.46 METs), whereas the morning group showed higher cardiorespiratory fitness (mean beta coefficient, 0.25 METs).
Researchers also observed differences in analyses stratified by sex. Among men, cardiorespiratory fitness was lower for the midday exercise group (–0.46 METs) and tended to be higher for men in the morning group (0.36 METS) vs. the mixed group (P for trend = .02), independent of the volume of bout-related physical activity and mean bout intensity. Among women, participants in the mixed group were the least fit, according to researchers.
In assessing risk for coronary heart disease, researchers found that 4-year FRS was not associated with the timing of exercise bouts among women; however, such a trend was observed for men (P = .01). Men in the inactive and morning exercise groups had a higher 4-year FRS vs. men in the mixed timing group, equivalent to an approximately one-fifth increase of the average CHD risk among all men in the cohort. Results persisted after adjustment for cardiorespiratory fitness.
“In particular, the male morning [exercise] group had the highest 4-year FRS, showing a 2.18% higher adjusted probability of developing CHD than the mixed group,” the researchers wrote.
Exercise ‘when you can’
The researchers cautioned that other factors not available in the Look AHEAD analysis, such as timing of food intake, sleep duration and occupation, may also play a role in associations between morning bout-related moderate- to vigorous-intensity physical activity and CHD risks.
“From these data, we cannot determine if performing exercise in the morning, for example, is better or worse compared with other times of day,” Middelbeek said. “The data are collected at only one point in time, and people were not assigned to be active at a specific time of day.”
Middelbeek said, until recently, physical activity data were primarily looked at in the context of total amount of physical activity performed.
“In future studies, it will be important for researchers to start looking deeper into at what time of day people are active and how that affects outcomes,” he said. “Increasing physical activity, at any time of day, is and remains one of the best things people with and without type 2 diabetes can do for their overall health.”
In a press release announcing the findings, Jingyi Qian, PhD, of the division of sleep and circadian disorders at Brigham and Women’s Hospital, said any physical activity — no matter what time of day — can provide benefits for patients.
“The general message for our patient population remains that you should exercise whenever you can, as regular exercise provides significant benefits for health,” Qian said in the release. “But researchers studying the effects of physical activity should take into account timing as an additional consideration so that we can give better recommendations to the general public about how time of day may affect the relationship between exercise and cardiovascular health.”
For more information:
Roeland J.W. Middelbeek, MD, MSc, can be reached at roeland.middelbeek@joslin.harvard.edu.
Perspective
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Patrick Schrauwen, PhD
Exercise is well known for its beneficial effects on metabolic and cardiovascular health. The study by Qian and colleagues investigated the impact of timing of daily activities on CV risk and found that — in men only — volunteers performing most of their moderate to vigorous physical activity in the morning had a higher CV risk. The study is the next in a line of recent publications suggesting that timing of exercise may affect metabolic health. As one of the first, a study by Mladen Savikj, MD, and colleagues (Diabetologia 2019; doi:10.1007/s00125-018-4767v) showed that afternoon exercise was more efficacious than morning exercise at improving blood glucose for people with type 2 diabetes. Recently, in a retrospective analysis of previously published exercise training data, we similarly showed that afternoon exercise may lead to more beneficial metabolic training adaptations after 12 weeks of exercise training (Mancilla R, et al. Physiol Rep. 2021; doi:10.14814/phy2.14669).
How timing of exercise may affect health outcomes is so far unknown; however, it likely involves interference with our biological clock. This molecular clock, which is both localized in our central system and also in peripheral tissues, dictates a 24-hour rhythm of many biological processes in our body, among which metabolism is a major clock-regulated process. There are indications that 24-hour rhythms are disturbed in metabolically compromised volunteers, such as people with type 2 diabetes.
Longitudinal studies are needed to investigate how timing of exercise may impact the biological clock and if it can help to reset our biological clock. Such information may help to further fine-tune exercise training programs for improvement of metabolic health. Until then, for most people, exercise performed at any time remains better than no exercise.
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