A compliant tendon increases fatigue resistance and net efficiency during fatiguing cyclic contractions of mouse soleus muscle

Aim: As muscles fatigue, their ability to generate mechanical work decreases as a result of decreased force generation and in cyclic activity, slower the relaxation. The purpose of this study was to determine whether a compliant tendon, connected in series with a muscle, would increase sustained work output during cyclic contractions. Methods: Experiments were performed in vitro (37°C) using fibre bundles from mouse soleus muscles (n=7). Each muscle performed two series of 40 brief contractions at a contraction frequency of 2Hz and with a sinusoidal length change. One series was performed using the fibre bundle only and one with the fibre bundle and a compliant strip of latex connected between the muscle and the force recording apparatus. Results: When contracting with the latex strip, muscle work output was better maintained during the second half of the protocol than when performed without the latex, overall energy cost was reduced and mechanical efficiency was increased. Conclusion: The provision of a compliant tendon analogue increased the level of work output that could be sustained during cyclic contractions and reduced energy expenditure. It is proposed that both metabolic and mechanical consequences of the compliant tendon contribute to the improved performance.