CIRCADIAN-RHYTHM IN THE TORQUE DEVELOPED BY ELBOW FLEXORS DURING ISOMETRIC CONTRACTION, EFFECT OF SAMPLING SCHEDULES

Time-dependent changes in elbow flexion torque have been documented ac cording to two different sampling schedules. Seven physical education students took part in the first series of experiments, and 7 other sim ilar subjects in the second. In both sets of experiments, the subjects performed isometric contractions: maximal and submaximal at 90 degree s in the first experiments and maximal at different angular positions in the second. After a 30-minute rest period, the torque developed was measured at 00:00, 06:00, 09:00, 12:00, 15:00, 18:00, and 21:00h on t he day of the experiment. These subjects remained in the laboratory fo r 24h. In the second series of experiments, the torque developed was m easured at 01:00, 05:00, 09:00, 13:00, 17:00, and 21:00h over the subs equent 6 days with only one lest session per day. In this case, there was an interval of 20h between two successive test sessions. In the fi rst experiment, a significant time-of-day effect was observed for the torque of the elbow flexors under isometric conditions with an acropha se at 17:58h. The 24h normalized mean score was 92.85% with an amplitu de of 7.63% of the daily mean. In the second series of experiments, th ere was evidence of a circadian rhythm in the torque developed by the elbow flexors at every angle position, especially at 90 degrees, the a ngle investigated in the first set of experiments. The peak torque was calculated to have occurred at 17:55h. The amplitude of the rhythm wa s equal to 6.99% of the daily mean. There were no statistically signif icant differences in the characteristics of the circadian rhythm obser ved between the two experimental designs. We concluded that an experim ent extending over several days could be employed to evaluate circadia n rhythms in muscular activity reliably.