TY - JOUR
T1 - Transducer and base compliance alter the in situ 6 dof force measured from muscle during an isometric contraction in a multi-joint limb
AU - Sandercock, Thomas G.
AU - Hoon Yeo, Sang
AU - Pai, Dinesh K.
AU - Tresch, Matthew C.
N1 - Funding Information:
This research was supported by NIH NIAMS R01AR053608 and NIH NINDS R21NS061208 to MCT and by the Canada Research Chairs Program, NSERC, and Peter Wall Institute for Advanced Studies to DKP.
PY - 2012/4/5
Y1 - 2012/4/5
N2 - Although musculoskeletal models are commonly used, validating the muscle actions predicted by such models is often difficult. In situ isometric measurements are a possible solution. The base of the skeleton is immobilized and the endpoint of the limb is rigidly attached to a 6-axis force transducer. Individual muscles are stimulated and the resulting forces and moments recorded. Such analyses generally assume idealized conditions. In this study we have developed an analysis taking into account the compliances due to imperfect fixation of the skeleton, imperfect attachment of the force transducer, and extra degrees of freedom (dof) in the joints that sometimes become necessary in fixed end contractions. We use simulations of the rat hindlimb to illustrate the consequences of such compliances. We show that when the limb is overconstrained, i.e., when there are fewer dof within the limb than are restrained by the skeletal fixation, the compliances of the skeletal fixation and of the transducer attachment can significantly affect measured forces and moments. When the limb dofs and restrained dofs are matched, however, the measured forces and moments are independent of these compliances. We also show that this framework can be used to model limb dofs, so that rather than simply omitting dofs in which a limb does not move (e.g., abduction at the knee), the limited motion of the limb in these dofs can be more realistically modeled as a very low compliance. Finally, we discuss the practical implications of these results to experimental measurements of muscle actions.
AB - Although musculoskeletal models are commonly used, validating the muscle actions predicted by such models is often difficult. In situ isometric measurements are a possible solution. The base of the skeleton is immobilized and the endpoint of the limb is rigidly attached to a 6-axis force transducer. Individual muscles are stimulated and the resulting forces and moments recorded. Such analyses generally assume idealized conditions. In this study we have developed an analysis taking into account the compliances due to imperfect fixation of the skeleton, imperfect attachment of the force transducer, and extra degrees of freedom (dof) in the joints that sometimes become necessary in fixed end contractions. We use simulations of the rat hindlimb to illustrate the consequences of such compliances. We show that when the limb is overconstrained, i.e., when there are fewer dof within the limb than are restrained by the skeletal fixation, the compliances of the skeletal fixation and of the transducer attachment can significantly affect measured forces and moments. When the limb dofs and restrained dofs are matched, however, the measured forces and moments are independent of these compliances. We also show that this framework can be used to model limb dofs, so that rather than simply omitting dofs in which a limb does not move (e.g., abduction at the knee), the limited motion of the limb in these dofs can be more realistically modeled as a very low compliance. Finally, we discuss the practical implications of these results to experimental measurements of muscle actions.
KW - Model
KW - Muscle
KW - Musclo-skeletal
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U2 - 10.1016/j.jbiomech.2012.01.005
DO - 10.1016/j.jbiomech.2012.01.005
M3 - Article
C2 - 22304843
AN - SCOPUS:84858624874
SN - 0021-9290
VL - 45
SP - 1017
EP - 1022
JO - Journal of Biomechanics
JF - Journal of Biomechanics
IS - 6
ER -