Circadian variability of bioelectric muscle tone in static and dynamic anaerobic exercises in men

Physiological processes in the body are characterized by a 24-hour circadian rhythm. The circadian variability of physiological processes affects exercise capacity. The aim of the study was to determine the circadian variability of bioelectric muscle tone in static and dynamic exercises with the use of surface electromyography (sEMG), which allows for the assessment of neuromuscular activity and muscle function during physical activity. Methods: The research sample consisted of 16 men aged 21.6 ± 0.62 years, with intermediate chronotypes, who were not professional athletes. The tests were conducted at 2:00, 10:00, 18:00 and 22:00 and included measurements of bioelectric tension (sEMG) of the vastus lateralis muscle of the right and left limbs during static exercise with maximum voluntary isometric contraction (MVC) and during dynamic exercise, such as the Jumping test – vertical jump with arm swing (CMJ) and without arm swing (ACMJ), as well as during a 10-second cycle ergometer test. The tests were repeated after 24 hours. Results: The circadian periodization of biopotential has a varied course with a noticeable decline in values at night time. The level of bioelectric tension recorded during static exercise did not show significant circadian variability. However, in dynamic exercises, significant variability ( p < 0.05) in bioelectric tension (sEMG) of the vastus lateralis muscle of the left limb during the Jumping test with arm swing (CMJ) was observed between 22:00 and 18:00 in the first series of tests. A tendency to achieve higher average amplitude values was observed at 10:00 in both limbs, with the lowest values observed at 2:00. After 24 hours, the highest bioelectric activity was observed in both limbs at 10:00 during the jump with arm swing (CMJ), while the lowest values in the left limb were observed at 2:00. During the jump without arm swing (ACMJ), the lowest level of bioelectric activity of the tested muscle in the right limb was observed at 2:00. In the 10-second anaerobic cycle ergometer test, significant variability ( p < 0.05) in bioelectric tension of the muscle in the left limb was shown between 18:00 (highest result) and 2:00 (lowest result). After 24 hours, the measurement values were generally lower compared to the results of identical measurements from the first series of tests. Conclusions: the level of bioelectric tension in the studied muscles during anaerobic exercises at different times of the day varies depending on the time and type of workout. The highest sEMG biopotential amplitude values were recorded in the evening and afternoon, while the lowest values were recorded at night time, at 2:00.