Estimation of musculoskeletal models from in situ measurements of XXXX in the @entity35 hindlimb.

@entity35 @entity25755 @entity121 @entity17633
Musculoskeletal models are often created by making detailed anatomical measurements of muscle properties. These measurements can then be used to determine the parameters of canonical models of @entity121 . We describe here a complementary approach for developing and validating muscle models, using in situ measurements of muscle actions. We characterized the actions of two @entity35 hindlimb muscles: the gracilis posticus ( @entity17633 ) and the posterior head of biceps femoris ( @entity25755 ; excluding the anterior head with vertebral origin). The @entity17633 is a relatively simple muscle, with a circumscribed origin and insertion. The @entity25755 is more complex, with an insertion distributed along the tibia. We measured the six-dimensional isometric forces and moments at the ankle evoked from stimulating each muscle at a range of limb configurations. The variation of forces and moments across the workspace provides a succinct characterization of @entity121 . We then used this data to create a simple muscle model with a single point insertion and origin. The model parameters were optimized to best explain the observed force-moment data. This model explained the relatively simple muscle, @entity17633 , very well (R(2)>0.85). Surprisingly, this simple model was also able to explain the action of the @entity25755 , despite its greater complexity (R(2)>0.84). We then compared the actions observed here with those predicted using recently published anatomical measurements. Although the forces and moments predicted for the @entity17633 were very similar to those observed here, the predictions for the @entity25755 differed. These results show the potential utility of the approach described here for the development and refinement of musculoskeletal models based on in situ measurements of muscle actions.
