Immobilization-induced increase in fatigue resistance is not explained by changes in the muscle metaboreflex.

Immobilization has been reported to enhance fatigability, which is paradoxical in light of the metabolic and molecular alterations that occur in atrophied muscles. We examined whether the immobilization-induced enhancement in fatigability was associated with attenuation in the muscle metaboreflex response. Ten subjects were examined after 3 weeks of hand-forearm immobilization. The time to task failure of a handgrip contraction (20% intensity) was determined along with heart rate (HR) and mean arterial pressure (MAP) at rest, during the task and during a 2-min postexercise muscle ischemia (PEMI) test that continues to stimulate the metaboreflex. Immobilization decreased strength by 25% (P<0.01) and increased the time to task failure by 21% (P=0.03). However, no changes were observed for the HR and MAP responses to the exercise task or during PEMI (P>0.05). These findings indicate that the augmentation of time to task failure with immobilization is not associated with changes in the pressor or metaboreflex responses.