JOINED EFFECTS OF PENNATION ANGLE AND TENDON COMPLIANCE ON FIBER LENGTH IN ISOMETRIC CONTRACTIONS - A SIMULATION STUDY

The main purpose of this study was to investigate the joined behaviour s of tendon and pennation angle during maximal isometric contractions. A musculotendon model of the human soleus muscle was simulated as a f unction of ankle joint position which determines the soleus length. An alysis of the respective values of tendon length and pennation angle f or various musculotendon lengths showed that the primary effects of te ndon elasticity and pennation angle variation were to reduce the fibre length variations by absorption of the musculotendon lengthening. The efficiency of this reduction process was the highest at short soleus lengths and principally related to tendon length variations. Finally, it was suggested that the optimal solution for musculotendon actuators acting in high lengthening ranges were long tendon units and great pe nnation angles. The heuristic model used in this study highlighted the existence of some dynamic phenomena inside the actuator However it di d not pretend to represent the overall complexity of the mechanical in teractions between the different elements composing the soleus archite cture.