Sport shifts the internal clock

Training at the right time could help with jet lag and shift work

Sport at the right time can have a positive effect on our inner rhythm. © Pavel, Narith / thinkstock
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The timing is crucial: Sport obviously can adjust our internal clock - depending on the time of training either forward or back, as an experiment with about 100 subjects suggests. According to Sport, in the morning and in the early afternoon, the inner rhythm is more likely to shift forward, while training in the evening allows the inner clock to follow. Thus, targeted sports could perhaps help with jet lag and shift work.

A variety of processes in our body are influenced by the rhythm of our internal clock. The range extends from the release of certain hormones such as the Müdemacher melatonin, the work of the internal organs, wound healing to the processing of sensory stimuli and our mood. Accordingly, it is problematic when these finely tuned rhythms get out of step, for example, by jet lag or shift work.

Training for the internal clock

But against the jet lag and a distorted internal clock could help a very simple means: Sport. However, it depends on when, as Shawn Youngstedt of Arizona State University and his team have found out. Their study involved 48 younger and 53 older men and women.

In order to switch off the normal outside day-night signalers, all participants lived in an artificial ultrashort rhythm for five days: a 60-minute wakefulness followed by a 30-minute rest period. After a day of familiarization, the researchers determined the individual clock of the internal clock for all subjects. For this, they analyzed a urine sample every 90 minutes for the content of the sleep hormone melatonin.

Now the actual experiment followed: Each subject trained for three days daily for one hour on a treadmill or crosstrainer. Each participant was assigned one of eight training times distributed throughout the day and night. This allowed them to specifically compare the effect of sports in the morning, lunch or evening on the internal clock. display

Clock adjusted

The result: If sport takes place at the right time of the day, he can adjust the internal clock. Training in the morning at seven o'clock or in the afternoon between 1 and 4 o'clock shifts the internal rhythm forward. In the experiment, the internal clock of the participants was about 90 minutes before.

It is different when you do sports in the evening between 19:00 and 22:00 o'clock: This makes the inner clock more like it. As a result, the subjects shifted the peak of melatonin secretion backwards by about two hours. There were no changes in the internal rhythm, if the participants trained at night between one and four or in the morning at ten o'clock, as the researchers report.

Help with jet lag and shift work?

"This is the first study that compares in detail the effect of the sport on the inner clock, " says Youngstedt. "We have clearly shown when the training will introduce the clock and when it will be followed." However, it is not yet clear how strongly these effects manifest themselves in the presence of normal external clocks. But the movement at the right time could possibly increase their effect and thus synchronize the internal clock.

Thus, sport could be a very useful tool against jet lag and the negative effects of shiftwork. Training at the appropriate time can then help to bring our inner clock back into the right rhythm. "In addition, there is evidence that regular sport also promotes the synchronization of muscles and other peripheral organ clocks, " the researchers explain.

The scientists also suspect that the effect of the sport on the internal clock can even be strengthened for example by bright light during training or even more intensive exercises. This has already been shown in animal experiments, says Youngstedt and his colleagues. (The Journal of Physiology, 2019; doi: 10.1113 / JP276943)

The Physiological Society

- Nadja Podbregar