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Two articles published on April 18 in the newspaper Cell metabolism confirm that the circadian clock is an important factor in the body's response to physical exertion. The studies focused on different components of the exercise, complementing each other. Based on this work alone, it is too early to say when the best time is for you to go jogging. But at least in the laboratory, evening exercises seem more productive, even though the lifestyles of human beings are much more complicated and this area of research is just beginning.
"We all know that almost every aspect of our physiology and metabolism is dictated by the circadian clock," says Gad Asher of the Department of Biomolecular Sciences at the Weizmann Institute of Science, senior author of the 39, one of the studies. "This is true not only in humans, but in all light-sensitive organisms.We decided to ask if there was a link between the time of day and the performance of the exercise . "
"Circadian rhythms dominate everything we do," adds Paolo Sbadone-Corsi of the Center for Epigenetics and Metabolism at the University of California at Irvine, lead author of the other article. "Previous studies from our lab have suggested that at least 50% of our metabolism is circadian and that 50% of the metabolites in our body oscillate according to the circadian cycle." So it makes sense that exercise is the best One of the things touched. "
Both research teams examined the badociation between time of day and physical performance, mainly in mice. Because mice are nocturnal, one thing they had to do was to translate the timing of the mouse into human timing, distinguishing between the active phase and the resting phase of mice rather than using numbers on the clock.
The Asher group started by placing mice in treadmills at different times of the day during their active phase. They examined the exercise capacity of mice at different intensities and regimens and found that the overall performance of physical activity was significantly better (about 50% on average and higher in some protocols) in the morning hours. These daily differences were reduced in mice with mutant clocks, confirming the potential role of the clock in the observed variance in exercise performance.
To identify a potential determinant of daily variance in physical performance, they applied high-throughput transcriptomics and metabolomics to muscle tissue. The researchers found that, in response to an evening exercise performed in mice, there were higher rates of a metabolite called ZMP (ribonucleotide 5-aminoimidazole-4-carboxamide). The ZMP is known to activate metabolic pathways related to glycolysis and fatty acid oxidation via the activation of AMPK, which is a cellular metabolic regulator. Therefore, it is likely that it contributes to the increase in exercise capacity in the evening. "Interestingly, the ZMP is an endogenous badogue of AICAR. [aminoimidazole carboxamide riboside], a compound that some athletes use for doping, "said Asher.
The researchers also studied 12 humans and found similar effects. Overall, participants in the study had lower oxygen consumption during exercise in the evening than in the morning; this is reflected in better exercise efficiency.
The Sbadone-Corsi team also placed mice on treadmills, but their approach was different. Using transcriptomics and high throughput metabolomics to examine a wide range of possible factors, they characterized the changes in mouse muscle tissue that occur in response to exercise. This allowed them to examine processes such as glycolysis (which contributes to sugar metabolism and energy production) and lipid oxidation (fat burning).
They discovered that a protein called hypoxia-induced factor 1-alpha (HIF-1?) Plays an important role and that it is activated by exercise in different ways depending on of the hour. HIF-1? is a transcription factor known to stimulate certain genes according to the rate of oxygen in the tissues. "It makes sense that HIF-1 is important here, but we did not know until now that its levels fluctuated with time," says Sbadone-Corsi. "It's a new discovery."
According to the UC Irvine team's work, exercise seems to have the most beneficial impact on metabolism at the beginning of the active phase (equivalent to late morning in the US). Man) compared to the rest phase (in the evening).
The researchers note that while circadian clocks have been preserved throughout the evolution, the translation of results for humans is not so simple. One of the reasons is that chronotypes of humans vary more than those of mice living in a laboratory. "You can be a morning person or a night person, and these things have to be taken into account," says Sbadone-Corsi.
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