Does time of day affect the body’s response to exercise?

“It’s quite well known 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.

He goes on to state that “This is true not only in humans but in every organism that is sensitive to light. We decided to ask whether there is a connection between the time of day and exercise performance.” Gad Asher is also the senior author of one of the studies that has shown that the circadian clock is an important factor in how the body responds to physical exertion.

Senior author of another recent paper that has shown similar findings, out of the Center for Epigenetics and Metabolism at the University of California, Paolo Sassone-Corsi adds “Circadian rhythms dominate everything we do”. He goes on to say “Previous studies from our lab have suggested that at least 50% of our metabolism is circadian, and 50% of the metabolites in our body oscillate based on the circadian cycle. It makes sense that exercise would be one of the things that’s impacted.”

The researchers of these papers studied mice and humans in lab conditions and found that both mice and people who exercised in the evening had had lower oxygen consumption when compared to the morning; this translated to better exercise efficiency.

The researchers found that a protein called hypoxia-inducible factor 1-alpha (HIF-1?) has a crucial role and is activated by exercise in different ways depending on the time of day. HIF-1? is known to stimulate specific genes based on oxygen levels in the tissue. “It makes sense that HIF-1? would be important here, but until now we didn’t know that its levels fluctuate based on the time of day,” Sassone-Corsi says. “This is a new finding.”

Despite these findings being very convincing and exciting it is a little too early to make conclusive statements on the optimal time to exercise for performance. Sassone-Corsi says “You may be a morning person, or you may be a night person, and those things have to be taken into account”.

1. Saar Ezagouri, Ziv Zwighaft, Jonathan Sobel, Sébastien Baillieul, Stéphane Doutreleau, Benjamin Ladeuix, Marina Golik, Samuel Verges, Gad Asher. Physiological and Molecular Dissection of Daily Variance in Exercise Capacity. Cell Metabolism, 2019; DOI: 10.1016/j.cmet.2019.03.012
2. Shogo Sato, Astrid Linde Basse, Milena Schönke, Siwei Chen, Muntaha Samad, Ali Altıntaş, Rhianna C. Laker, Emilie Dalbram, Romain Barrès, Pierre Baldi, Jonas T. Treebak, Juleen R. Zierath, Paolo Sassone-Corsi. 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