Affiliations: [a] Centre de Recherches en Activités Physiques et
Sportives, CRAPS, UPRES EA 2131, Université de Caen-Basse Normandie, UFR
STAPS, 2 Boulevard du Maréchal Juin, 14032 Caen Cedex, France | [b] Laboratoire de biomécanique et physiologie,
Institut national des sports et de l'éducation physique, INSEP, 11 avenue
du Tremblay, 75012 Paris, France
Abstract: This study was conducted to describe the time-of-day effect on
muscle fatigue during both intermittent concentric (CE) and eccentric (EE)
exercises. A second aim was to examine whether the time of day at which the
exercise was performed influenced recovery of muscle strength. Ten male
subjects performed CE and EE consisting of 5 sets of 10 maximal voluntary
contractions (MVC) of the elbow flexors (angular velocity:
60°/s) at two different times (06:00 h and 18:00 h).
Torque and Electromyographic activities (EMG) of the biceps brachii and triceps
brachii were recorded before (Pre), during and immediately after (Post) each
fatiguing task. Furthermore, strength recovery was measured 2 days
(Post_{2d}), 3 days (Post_{3d})
and 7 days (Post_{7d}) after each fatiguing task.
Results showed that during CE, torque variations were greater at 18:00 h than
at 06:00 h. No time-of-day effect occurred during EE. Recovery time was faster
in the morning than in the evening for isometric MVC only. To conclude, unlike
the case in eccentric mode, mechanisms involved in concentric muscle action
appear to be time-of-day dependent, with a greater muscle capacity in the late
afternoon. Also, strength recovery is greater when fatiguing exercises are
performed in the early morning than in the late afternoon.
Keywords: Circadian rhythm, electromyography, time recovery, maximal effort, neuromuscular efficiency
