Master of Science
Gribble, Paul L.
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.
Summary for Lay Audience
Proprioception is our sense of limb position. Previous studies have sought to determine if the accuracy of proprioception is different when we are engaged in movements that we generate ourselves (e.g., when reaching toward an object), compared to when we are engaged in movements that we do not generate ourselves (e.g., when someone else is guiding our hand towards an object). In real life, our movements are not usually passively guided by someone else; however, they can be (and often are) driven by forces other than the ones our muscles exert on our limbs to move them. For example, when the right arm is used to reach towards an object that is located to the right of the body, the elbow extends primarily because our elbow extensor muscles are producing forces that rotate the forearm relative to the upper arm—that is, the rotational forces (i.e., torques) driving movement mostly come from our muscles. But when the right arm is used to reach to an object that is located to the left of the body, the elbow's extension is primarily driven by the rotation of the upper arm about the shoulder joint, not by forces exerted by our elbow extensor muscles. Thus, elbow extension can be driven not just by the torque our muscles actively produce, but also by torque that is produced by the passive interactions of limb segments that are attached to each other in the multijoint human arm. This provides the basis for a more naturalistic way to examine whether proprioception differs during movements that we do or do not generate ourselves: in this study, we will compare proprioception at the elbow joint when joint motion does (muscle torque-driven motion) or does not (interaction torque-driven motion) result from the activity of the muscles that are responsible for moving that joint.
Heidari, Peyman R., "The influence of intersegmental dynamics on limb position sense" (2022). Electronic Thesis and Dissertation Repository. 8872.
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