Bipennate Arrangement of Soleus Muscle in Human and its Relevance to the Force of Contraction

Abstract

Soleus muscle exhibits bipennate arrangement on its centro-anterior aspect and the longitudinal parallel muscle fibers on its posterior and lateral margins. Till date soleus muscle was studied as a whole muscle with less attention given on its bipennate arrangement. As per according to standard texts, increase in cross sectional area due to bipennate arrangement in soleus muscle augments the power and force of contraction.The current study was done on 50 cadaveric lower limbs. Out of them 25 were of right side and 25 were of left side. The soleus muscle was divided into four equidistant hypothetical segments i.e- I, II, III, IV by imaginary lines drawn from the highest point of origin of muscle fibers to the lowest point of merging of muscle fibers to the tendocalcaneus. In 6% of cases the pennation was not clearly visible as it was covered anteriorly with nonseparable fascial sheath due to its adherence to subfascial muscle fibers. In 94% of cases pennation was present, out of which 6% cases showed pennation from segment I to IV, 4% cases showed pennation from segment I to III, 42% cases showed pennation from segment II to IV and 38% cases showed pennation from segments II to III, while 4% cases showed pennation only in segment III. The width, length and angle of muscle fasciculus of pennation are maximum in segment II.