Muscle fatigue of the elbow flexor muscles during two intermittent exercise protocols with equal mean muscle loading

Objective. Whether different muscle-loading patterns with the same mean load have a similar influence on the resultant muscle fatigue is still unknown. This study investigated the influence of two intermittent exercise protocols, with equal mean muscle loading, on the mechanical and myoelectrical signs of fatigue in the elbow flexor muscles. Design. Ten subjects performed two 20-min long intermittent isometric elbow flexion tasks. The exercise period load for the low force intermittent test was 25% of the maximum voluntary contraction, with a work-cycle time of 20 s and a duty cycle of 0.5. The high force intermittent exercise protocol had an exercise period load of 50% maximum voluntary contraction, a cycle time of 20 s and a duty cycle of 0.25. Methods. Muscle fatigue was quantified both by measuring the maximal voluntary contraction torque before and after the intermittent exercises, and also by the temporal changes observed in the electromyography signal. Results. Both muscle-loading patterns induced a 15% decrease in maximum voluntary contraction. However, the electromyographic spectral changes during the intermittent static contractions varied between the two protocols. Conclusions. Variation in muscle load without loss in productivity can affect the physiological responses. The results also showed that different methods to assess muscle fatigue sometimes provide different information on the resultant fatigue.