Diurnal Rhythm of the Muscular Performance of Elbow Flexors During Isometric Contractions

Abstract

The influence of time of day on elbow flexion torque was studied. Thirteen physical education students, 7 males and 6 females, made maximal and submaximal isometric contractions at 90 degrees of elbow flexors using a dynamometer. The torque developed was measured on each contraction. The myoelectric activity of the biceps muscle was also measured at the same time by surface electromyography (EMG) and quantified from the root mean square (RMS) activity. Torque and surface EMGs were measured at 6:00, 9:00, 12:00, 15:00, 18:00, 21:00, and 24:00 h over the same day. Oral temperature before each test session was measured on each occasion after a 30-min rest period. We observed a diurnal rhythm in elbow flexor torque with an acrophase at 18:00 h and a bathyphase at 6:00 h, in phase with the diurnal rhythm in oral temperature. However, the diurnal rhythm of temperature did not appear to have any influence on the torque. Links between neuromuscular efficiency and RMS/torque ratio were evaluated by measuring muscle activity along with torque. We also assessed variations in the level of maximal activity of the muscle under maximal voluntary contraction. Neuromuscular efficiency fluctuated during the day, with maximal and minimal efficiency at 18:00 h and 9:00 h, respectively, whereas activation level was maximal at 18:00 h and minimal at 9:00 h. The diurnal rhythm of torque was accounted for by variations in both central nervous system command and the contractile state of the muscle.

Role of biological rhythms in the performance of physical activity

“…Technical skills in particular have been found to be greatest in the afternoon [52][53][54] . The peak is reached in the evening, such as muscular strength and anaerobic performance [55][56][57][58][59][60][61] . Technical skills require a higher degree of exercise control, so they peak earlier 62) .…”

Phase-adjustment of human circadian rhythms by light and physical exercise

“…In general, the rhythms of different aspects of sports performance are associated with that of core body temperature. Peak performance occurs in the early evening, around the time of maximum core body temperature, whereas worst performance is in the early morning around the time of the minimum temperature 32,33) . Body temperature is affected not only by the circadian pacemaker in the SCN but also by external factors such as environmental temperature, the individual's health and sleep, which factors directly moderate body temperature (masking factors).…”

EMG vs Precision and Accurancy in Dentistry

“…Then, it increases until 11:00 a.m. -1:00 p.m. High values also occur in the afternoon and evening [10,31]. The amplitude of the effort record reaches its maximum value about 6:00 p.m. [32]. Daily fluctuation of the temperature measured on the surface of the skin correlates visibly with the cyclical change of motor units efficiency.…”