Resting length of the human soleus muscle.

The quantitative relationship between soleus muscle length and the angle of the ankle joint was studied in human cadaver lower limbs of various lengths. The ratio of soleus length to fibula length (lsol/lfib) was linearly related to ankle angle phi A. An expression for soleus resting length lr was derived from the parameters of this relationship and lr was estimated to be 0.998 lfib (S.E. of estimate = 0.004, P less than 0.0001). This gave a mean (+/- S.D.) value of lr of 361.4 (+/- 16.9) mm. The fractional change of lsol produced by rotation of the ankle joint was 0.004 lr.deg-1. The results of these analyses are used to predict lsol changes in intact subjects under varying experimental conditions.