Summary: A new study reports the time of day at which you exercise can shift your body clock. The findings suggest exercise could counter the negative health effects associated with shift work and jet lag.
Source: The Physiological Society.
Exercise can shift the human body clock, with the direction and amount of this effect depending on the time of day or night in which people exercise. That’s according to new research in published in The Journal of Physiology. These findings suggest exercise could counter the effects of jet lag, shift work, and other disruptions to the body’s internal clock (e.g. military deployments) helping individuals adjust to shifted schedules.
The circadian “body”‘ clock is the 24 hour cycle that regulates many physiological processes including sleeping and eating. Many factors affect this internal body clock including light and time cues. Exercise has been known to cause shifts in the circadian clock however very little is known about this effect.
This study found that exercising at 7 am or between 1 and 4 pm advanced the body clock to an earlier time, and exercising between 7 and10 pm delayed the body clock to a later time. Exercising between 1 and 4 am and at 10 am, however, had little effect on the body clock, and the phase-shifting effects of exercise did not differ based on age nor gender.
The researchers at University of California, San Diego and Arizona State University examined body clocks following exercise in 101 participants for up to five and a half days. The baseline timing of each participant’s body clock was determined from urine samples collected every 90 minutes to measure the time of the evening rise in melatonin and the peak of melatonin several hours later. Participants then walked or ran on a treadmill at a moderate intensity for one hour per day for three consecutive days. They exercised at one of eight different times of day or night, but each individual exercised at the same time on all three days or nights. The timing of the body clock was re-assessed following the third exercise session.
Given that the subjects tested were more physically active than average, the results might not translate to the average person. Further research will look at combining exercise with bright lights and melatonin to see what impact this has on body clocks, as well as examining the effect of changes in exercise duration and intensity on the body clock.
Shawn Youngstedt, first author on the paper, said:
“Exercise has been known to cause changes to our body clock. We were able to clearly show in this study when exercise delays the body clock and when it advances it. This is the first study to compare exercise’s effects on the body clock, and could open up the possibility of using exercise to help counter the negative effects of jet lag and shift work.”
Funding: This research was supported by the National Institutes of Health.
Source: Julia Turan – The Physiological Society
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is credited to Kathryn Elliott.
Original Research: Abstract for “Human Circadian Phase‐Response Curves for Exercise” by Shawn D. Youngstedt, Jeffrey A. Elliott, and Daniel F. Kripke in Journal of Physiology. Published February 19 2019.
Human Circadian Phase‐Response Curves for Exercise
Although bright light is regarded as the primary circadian zeitgeber, its limitations support exploring alternative zeitgebers. Exercise elicits significant circadian phase‐shifting effects, but fundamental information regarding these effects is needed. The primary aim of this study was to establish phase‐response curves (PRC) documenting the size and direction of phase shifts in relation to the circadian time of exercise. Aerobically fit older (n = 51, 59–75 y) and young adults (n = 48, 18–30 y) followed a 90‐min laboratory ultra‐short sleep wake cycle (60 min wake/30 min sleep) for up to 5 ½ days. At the same clock time on three consecutive days, each participant performed 60 min of moderate treadmill exercise (65‐75% of heart rate reserve) at one of 8 times of day/night. To describe PRCs, phase shifts were measured for the cosine‐fitted acrophase of urinary 6‐sulphatoxymelatonin (aMT6s), as well as for the evening rise, morning decline, and change in duration of aMT6s excretion. Significant PRCs were found for aMT6s acrophase, onset and duration, with peak phase advances corresponding to clock times of 7 AM and 1PM‐4PM, delays from 7 PM‐10 PM, and minimal shifts around 4 PM and 2 AM. There were no significant age or sex differences. The amplitudes of the aMT6s onset and acrophase PRCs are comparable to expectations for bright light of equal duration. The phase advance to afternoon exercise and the exercise‐induced PRC for change in aMT6s duration are novel findings. The results support further research exploring additive phase shifting effects of bright light and exercise and health benefits.