Affiliations: [a] Centre de Recherches en Activités Physiques et
Sportives (CRAPS), UPRES EA 2131, Université de Cane, France | [b] Département de Kinésiologie, Université de
Montréal, Montréal, Canada
Note: [] Address for correspondence: A. Nicolas, Centre de Recherches en
Activitès Physiques et Sportives (CRAPS, UPRES EA 2131), Université de
Caen – Basse Normandie, UFR STAPS, 2 Boulevard du Maréchal Juin, 14032
Caen Cedex, France. Tel.: +33 231 56 72 83; Fax: +33 231 56 72 82; E-mail:
arnaud.nicolas@unicaen.fr
Abstract: We investigated the effect on neuromuscular properties of the knee
extensors of an exhaustive cycling exercise performed at 6AM and 6PM. Eleven
well trained cyclists performed a maximal aerobic exercise consisting in a
sustained effort at 95% of their maximal power until exhaustion
(T_{lim}). Isometric maximal voluntary contraction (MVC)
and electromyographic activities (root mean square: RMS) of the vastus
lateralis were recorded before (pre-test) and immediately after (post-test) the
cycling exercise. The MVC/RMS ratio was calculated and used as an index of
neuromuscular efficiency (NME). Rectal temperature was recorded continuously
throughout the test session. Results show that T_{lim}
cycling exercise was not time-of-day dependent (p=0.42). A
significant interaction effect of time of day and the cycling exercise was
demonstrated for MVC (p<0.02) and NME
(p<0.05). In pre-test, MVC and NME were higher in the late
afternoon than in the morning (+6.8%); however both
parameters were more affected by the T_{lim} exercise at
6PM than at 6AM. These results suggest that following cycling T_{lim}
exercise, neuromuscular properties of the knee extensors are
more affected in the evening than in the morning. However, circadian rhythm of
some biomechanical parameters implicated in the pedalling movement may modulate
the effect of these diurnal variations.
Keywords: Diurnal variation, muscle fatigue, electromyography, limited time, MVC
