The influence of intersegmental dynamics on limb position sense
Abstract
During multijoint limb movement, the motion of limb segments can be driven actively, by muscle torque, and/or passively, by interaction torque–rotational force that arises passively at one joint due to motion of an adjacent limb segment about another joint. Proprioception plays a critical role in compensating for interaction torques, and deafferented patients have marked deficits in this aspect of motor control. This observation is seemingly at odds with the widely-held belief that proprioceptive sense is poor during motion that is not driven by active muscle contraction, and suggests that proprioceptive acuity might be preserved during motion that is driven by interaction torque. We designed a study to determine whether the nature of the torques driving joint motion influences proprioceptive sense at that joint. We quantified proprioceptive acuity at the elbow joint while participants were midway through each of two kinds of reaching movements that both involved elbow extension: one in which extension was primarily driven passively by interaction torques, and another in which extension was primarily driven actively by elbow muscle torques. We delivered equally sized and timed perturbations to the elbow joint during motion. Participants’ ability to correctly sense the direction in which the elbow was perturbed (flexion or extension) differed depending on if the perturbation was delivered during interaction torque-driven motion or active muscle torque-driven motion. Specifically, participants had superior perceptual acuity when joint motion was driven by interaction torque, suggesting that proprioceptive sense is preserved during this type of motion.