Researchers from the University of Copenhagen have learned that the effect of exercise may differ depending on the time of day it is performed.
In mice, they demonstrate that exercise in the morning results in an increased metabolic response in skeletal muscle, while exercise later in the day increases energy expenditure for an extended period of time.
We probably all know how important a healthy circadian rhythm is.
Too little sleep can have severe health consequences.
But researchers are still making new discoveries confirming that the body’s circadian clock affects our health.
Now, researchers from University of Copenhagen – in collaboration with researchers from University of California, Irvine – have learned that the effect of exercise may differ depending on the time of day it is performed.
Studies in mice reveal that the effect of exercise performed in the beginning of their dark/active phase, corresponding to morning, differs from the effect of exercise performed in the beginning of the light/resting phase, corresponding to evening.
“There appear to be rather significant differences between the effect of exercise performed in the morning and evening, and these differences are probably controlled by the body’s circadian clock.
Morning exercise initiates gene programs in the muscle cells, making them more effective and better capable of metabolizing sugar and fat.
Evening exercise, on the other hand, increases whole body energy expenditure for an extended period of time,” says one of the researchers behind the study, Associate Professor Jonas Thue Treebak from the Novo Nordisk Foundation Center for Basic Metabolic Research.
Credit: University of Copenhagen, Faculty of Health and Medical Sciences.
Morning exercise is not necessarily better than evening exercise
The researchers measured a number of effects in the muscle cells, including the transcriptional response and effects on the metabolites.
The results show that responses are far stronger in both areas following exercise in the morning and that this is likely to be controlled by a central mechanism involving the protein HIF1-alfa, which directly regulates the body’s circadian clock.
Morning exercise appears to increase the ability of muscle cells to metabolize sugar and fat, and this type of effect interests the researchers in relation to people with severe overweight and type 2 diabetes.
On the other hand, the results also show that exercise in the evening increases energy expenditure in the hours after exercise.
Therefore, the researchers cannot necessarily conclude that exercise in the morning is better than exercise in the evening, Jonas Thue Treebak stresses.
“On this basis we cannot say for certain which is best, exercise in the morning or exercise in the evening.
At this point, we can only conclude that the effects of the two appear to differ, and we certainly have to do more work to determine the potential mechanisms for the beneficial effects of exercise training performed at these two time-points.
We are eager to extend these studies to humans to identify if timed exercise can be used as a treatment strategy for people with metabolic diseases,” he explains.
The article behind the new research results will be published in the next issue of Cell Metabolism.
Increased muscle strength and cardiac fitness reflect regular physical activity.1, 2, 3 This reflection is strongly associated with time-dependent exercise.4, 5 Recent studies have attempted to elucidate the manner in which different exercise types and duration are involved in the regulation of several physiological responses through morning and evening exercise because this information is important in improving muscle fitness, aerobic capacity, and well-being.5, 6, 7, 8
The beneficial effect obtained from exercise is generally determined by multiple systems such as the motor, physiological, and neurobiological systems.9, 10, 11 In particular, physiological and neurobiological activities are dependent on biological rhythms in the human body; this is also known as circadian or diurnal rhythms.12, 13, 14, 15 This phenomenon has been widely described in time-of-day studies. Despite the fact that the data in the literature have shown a significant association between time and aerobic exercise,16, 17, 18 other studies have not indicated any such circadian variations.19, 20, 21 These results indicate that the time-course effects of aerobic exercise on maximal aerobic velocity and exhaustion time remain unclear.11, 14 Other reports have described the use of time-of-day for resistance exercise.22, 23, 24 The results of time variations during resistance exercise (which involve muscle strength, power, and sprint) range from 3% to 21.2%, depending on the individual being tested, the position of the muscles, and the experimental design.25, 26
The warm-up duration, sleep deprivation, and training time prior to exercise training can be affected by diurnal variation.27, 28 Sedliak et al29 report that exercise performed in the morning can improve muscle strength. However, another study obtained contradicting results and showed that participants were able to perform more physical activity in the evening, despite the lower physiological variation at this time.30 However, variations in the neuromuscular performance level increased during evening exercise. Thus, further information on the differences in the effects of morning and evening exercises is required. In this review, we discuss the exercise effects on aerobic and anaerobic performance, on short and long duration, and on hormone adaptation through time-of-day exercise studies.Go to:
2. Differential effect of exercise type
2.1. Aerobic training
In general, aerobic exercise plays a role in weight loss management,31 and improves peak maximal oxygen consumption (VO2max)32 and workload.33 Several studies have recently confirmed the presence of time-of-day effects of exercise on these variables.34, 35 Therefore, health and disease outcomes in response to exercise may depend on the time of day the exercise is performed.36, 37 Hobson et al38 suggest the existence of a time-of-day effect on aerobic exercise for improving aerobic exercise capacity. The authors observed that the endurance exercise capacity of men during exhaustive cycling exercise at 65% peak VO2 was significantly greater in the morning than in the evening. In addition, Shiotani et al30 found that a two-month aerobic exercise program, which consisted of ergometer cycling, increased the heart rate in the morning. However, another study found that an evening exercise training group had a greater work capacity after 5 weeks of high-intensity training, compared to the morning exercise training group.39 Faisal et al40 similarly indicated the presence of a time-of-day specificity on the effects of aerobic exercise training. Therefore, the studies in the literature indicate that different effects may be elicited, depending on the exercise duration, time, and the individual.
2.2. Resistance training
Resistance exercise elicits improved muscle strength and power, and elicits changes in anabolism/catabolism, depending on the time of the day.41, 42 Souissi et al43 found that, compared to evening exercise, morning exercise yielded more beneficial effects on anaerobic performance after 6 weeks of resistance training. After examining study participants who underwent resistance training for 6 weeks in the morning, Chtourou et al27 similarly noted that muscle performance–determined by the one-repetition, squat jump, and Wingate tests–was significantly higher among this group than among individuals who performed resistance training in the evening. By contrast, certain researchers have reported that evening exercise is more effective than morning exercise, and one study showed a significant improvement in peak muscle power in well-trained cyclists in the evening than in the morning.44 Furthermore, Edwards et al45 showed that grip strength, isokinetic knee flexion, peak power, and peak torque were higher in the evening than in the morning.
However, Sedliak et al46, 47 observed that after 10 weeks of exercise in a diurnal pattern the maximum isometric strength was not altered in the morning and evening. In a similar study, some researchers indicated that no time-of-day changes were observed in muscular anaerobic performance. Chtourou et al48 measured electromyography (EMG) activity in study participants performing the 30-second Wingate test in the morning and evening; however, the authors did not note any significant differences in EMG activity during the entire 30 seconds between the morning and evening exercise. In another study, Chtourou et al27 similarly indicated that, after 8 weeks of lower extremity progressive resistance training, the muscle strength was similar between the participants who performed the exercise in the morning and participants who performed the exercise in the evening. Sedliak et al47 did not show any time-of-day-specific adaptations during unilateral isometric knee extension peak torque training. Zarrouk et al49investigated the time-of-day effects on repeated sprint ability, but did not observe any significant time-of-day effects on the EMG activity levels of four thigh muscles during a repeated pedaling sprint exercise. Chtourou et al50 moreover showed no significant difference in muscular power or strength between the morning and evening tests. To understand better the time-of-day effects on muscle strength responses, future studies should assess the main physiological variations following resistance exercise adaptations.
2.3. Differential effect of exercise duration
Many scientists have investigated different exercise types, times, durations, and intensities of exercise training. Exercise duration is particularly important. Many studies have shown that short-term performance changes with different exercise times. In addition, short-term exercise training, which enhances anabolic metabolism, can be influenced by several factors such as time-of-day training.47, 51 In previous studies, exercise training improved anaerobic performance in the morning and/or evening29, 46 (Table 1). Most investigations have shown that evening exercise is better than morning exercise.27, 47, 50, 52 Souissi et al43 indicated that 6 weeks of resistance training in 10-year-old and 11-year-old boys improved muscle strength and power to a significantly greater extent in the evening than in the morning. Brisswalter et al53 investigated the effects of moderate exercise and determined that VO2 kinetics were significantly higher in the morning than in the evening. Souissi et al28 observed the effect of different exercise training times on anaerobic performance, including peak anaerobic power, jump performance, and peak knee extension toque. Their study found that the group that was trained in the evening had greater improvements in anaerobic performance. Lricollais et al54 moreover showed that, during the 60 second Wingate test, muscle fatigue was lower in the evening than in the morning.
able 1
The effect of time of day on short-term exercises.
| Refs | Participants | Age (y) | Measurement parameters | Acrophase | Amplitude |
|---|---|---|---|---|---|
| Atkinson et al69 | Trained (n = 7) Untrained (n = 7) | 19–29 Trained, 23.9 ± 3.3 Untrained, 24.3 ± 24 | Whole-body flexibility Back and leg strength Grip strength Flight time in a vertical jump Self-chosen work rate | 17:00–19:00 h | Trained > untrained (˜ 2–10% vs. ˜ 1–7%) |
| Wyse et al70 | 9 Collegiate sportsmen | 19.6 ± 9.6 | Extension peak torque Flexion peak torque | 18.00–19.30 h | ˜ 5–12% |
| Gauthier et al52 | 13 Physical education participants | M: 22.0 ± : 22.0 physical education | Elbow flexor torque | 18:00 h | ˜ 4% |
| Martin et al71 | 13 Healthy participants (12 M and 1 F) | 22–40 | MVC | 18:00 h | 8.9% |
| Callared et al72 | 6 M ultradistance cyclists | 33.4 ± 3.4 | MVC | 19:30 h | 6% |
| Souissi et al73 | 13 M physical education students | 22.4 ± 2.4 | Maximal power during the force velocity test | 18:00 h | 8.3% |
| Castaingts et al74 | 11 M | 18–30 | MVC | 18:00 h | 8.6% |
F, female; M, male; MVC, maximal voluntary contraction; NS, not significant.
Note. From “The effect of training at a specific time of day: a review”, by H. Chtourou and N. Souissi, 2012, J Strength Cond Res, 26, p.1984–2005. Copyright 2013, Wolters Kluwer Health. Reprinted with permission.
Long-term exercise has beneficial effects on aerobic capacity, cardiac function, and rehabilitation. In particular, this type of exercise is important in exercises involving time trials such as cycling, rowing, swimming, running, football, and table tennis. In a previous study, Deschenes et al21 observed that during aerobic exercise, the mean arterial blood pressure was higher in the morning than in the evening (Table 2). In agreement with these studies, Edwards et al55 investigated the effect of submaximal cycling at 60% of VO2max, and found that the morning exercise group exhibited greater improvements in lactate levels, compared to the evening exercise group.43 By contrast, Reilly and Garrett19 indicated a higher power output during a 60-minute cycle ergometer test in the evening than in the morning. Atkinson and Reilly13 also indicated that, after a 1.6-km time trail exercise, the heart rate and blood lactate levels exhibited greater improvements in the evening exercise group than in the morning exercise group. However, previous studies did not indicate any difference in the time-of-day effect on exhaustion during maximal19, 21 and submaximal cycling.55
Table 2
The effect of time of day on longterm exercises.
| Refs | Participants | Age (y) | Measurement parameters | Acrophase |
|---|---|---|---|---|
| Dalton et al20 | 7 M competitive cyclists or triathletes | 22.3 ± 2.3 | Total work during a timed trial cycling performance of 15-min duration Average power output during a time trial cycling performance of 15 min duration | NS |
| Bessot et al72, 75 | 10 M competitive endurance cyclists | 21.5 ± 1.5 | Free pedal rate during 4 × 5 min cycling exercise | NS |
| Edwards et al55 | 8 M recreational cyclists | 24.3 ± 4 | Work rate during 30-min submaximal cycling at 60% of VO2max | NS |
M, male; NS, not significant; VO2max, maximal oxygen consumption.
Note. From “The effect of training at a specific time of day: a review”, by H. Chtourou and N. Souissi, 2012, J Strength Cond Res, 26, p. 1984–2005. Copyright 2013, Wolters Kluwer Health. Reprinted with permission.
Hormone adaptation
The role of adrenal steroids in response to exercise training is very important for improving muscle cell and protein synthesis.56, 57, 58 Many researchers have revealed different time-of-day effects of anabolic hormones (such as testosterone and cortisol) on muscle strength and protein synthesis within skeletal muscle.6, 59, 60 Testosterone is a male sex hormone and its anabolic effects are observed during male adolescence and adulthood.61 During exercise training and physical activity, the main effect of testosterone is on insulin sensitivity and on the maintenance of muscle protein synthesis within the muscular system.62, 63
Cortisol is catabolic in nature, and is a stress hormone.64 Florini65 found that cortisol exerts catabolic effects on muscle tissue. Increased cortisol levels may also inhibit protein synthesis.66Testosterone and cortisol both exhibit diurnal variations in peak concentrations in the morning and/or evening.67 Florini65 observed increased cortisol levels in the morning, which may stimulate an increase in glucogenesis, proteolytic activity, and skeletal protein turnover.59 This effect may generate the catabolic status of muscle tissue. Increased testosterone levels may furthermore offset the effects of cortisol on skeletal protein degradation.68
Several investigators have indicated that hormonal responses can be influenced by the time of exercise training and the intensity, and duration of exercise. Sedliak et al29 indicated that testosterone levels did not change in response to resistance training in the morning. Another study showed that 10 weeks of training did not induce any significant differences in testosterone and cortisol levels.24 Deschenes et al21 also report that resistance exercise has no effect on the diurnal variations in cortisol and testosterone levels. However, Bird and Tarpenning23 showed that cortisol levels were lower in the evening than in the morning. These results suggest that the skeletal muscle metabolism may be improved at that time of the day. However, further research is required to support the use of different exercise timings, based on hormonal responses.
More information: Shogo Sato et al, Time of Exercise Specifies the Impact on Muscle Metabolic Pathways and Systemic Energy Homeostasis, Cell Metabolism (2019). DOI: 10.1016/j.cmet.2019.03.013
Journal information: Cell Metabolism
Provided by University of Copenhagen
