In vitro repeated work loop cycles in mouse soleus muscle demonstrate that fatigue reduces net work through decreased force and slowed relaxation, with frequency-dependent effects on power output.
Mouse soleus fatigue data should not guide clinical practice; leaves open human translation of frequency-dependent power loss.
The function of many muscles requires that they perform work. Fatigue of mouse soleus muscle was studied in vitro by subjecting it to repeated work loop cycles. Fatigue resulted in a reduction in force, a slowing of relaxation and in changes in the force-velocity properties of the muscle (indicated by changes in work loop shape). These effects interacted to reduce the positive work and to increase the negative work performed by the muscle, producing a decline in net work. Power output was sustained for longer and more cumulative work was performed with decreasing cycle frequency. However, absolute power output was highest at 5 Hz (the cycle frequency for maximum power output) until power fell below 20% of peak power. As cycle frequency increased, slowing of relaxation had greater effects in reducing the positive work and increasing the negative work performed by the muscle, compared with lower cycle frequencies.
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Askew et al. (1997) studied this question.
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