Isabella Chao 22′
Cardiac muscle tissue
The human body follows a circadian clock: the brain’s biological process based off of light-dark cycles, rest-activity patterns and feeding-fasting sequences. Recent research has focused on the role of this rhythm on the body’s response to physical exercise. A team lead by Shogo Sato examined whether mice’s circadian rhythm of their skeletal muscle’s metabolic pathways were differentially impacted by exercise at varying times throughout the day. The mice were separated into four groups called sedentary control (sed), early and late, and exercise (exe), early and late. Every four hour interval between hours zero and twenty, the mice were killed after one hour of acute exercise or other exercise on a treadmill. The treadmilling portion of the experiment at varying points during the day. After examining the mice at their respective times after exercise, the researchers noticed that the overall exercise performance is approximately 50% better in the evening – towards the end of the active time – in comparison to the morning. These results support the proposal that a circadian clock plays a role in varying exercise performances.
Another group of researchers lead by Sassone-Corsi utilized a similar exercise treatment, evaluating changes after mice exercised on treadmills. However, they specifically looked at the changes in the muscle tissue in response to exercise. They monitored glycolysis, the process of sugar metabolism, energy production, and lipid oxidation, which is also known as fat burning. They found a certain protein called HIF – 1? which triggers varying downstream cascades depending on the time of day of exercise.
Additionally, research has shown how the metabolite ZMP activates metabolic pathways related to glycolysis and fatty acid oxidation through the stimulation of AMPK, another metabolic regulator. Metabolites are general substances that are created during or needed for metabolic processes. This combination leads to a higher capacity for beneficial exercise in the evening. Sato’s team also examined twelve humans in their experiment, and they showed similar results to the mice. These young participants exercised at 8am and 6pm more than two and a half days apart. To control for the effects of confounding variables, they did not participate in an physical activity during the preceding days, nor did they drink alcohol or caffeine the day before or the day of the test. They also slept at least seven hours the night before the test and ate a meal two hours prior. The human subjects showed lowered oxygen consumption levels, blood glucose levels and heart rate after the 6 pm session, but the respiratory exchange ratio was higher later in the day. Essentially, there was no significant difference in ventilation and blood lactate levels between the two sessions. However, the perceived exertion by the individuals was lower in the later session.
In sum, research on exercise suggests that the greatest impact on the metabolism occurs during late mornings. However, it is still too early in the research process to come to a definite conclusion when the overall best time to exercise is. Humans are more complicated than mice, live varying lifestyles and function on slightly different, but analogous, circadian rhythms.
References:
- 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
- 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
- Cell Press. “Does time of day affect the body’s response to exercise?.” ScienceDaily. ScienceDaily, 18 April 2019. <www.sciencedaily.com/releases/2019/04/190418141722.htm>.