Abstract
A trailing joint control pattern, during which a single joint is rotated actively and the mechanical effect of this motion is used to move the other joints, was previously observed during simplified, laboratory-based tasks. We examined whether this simple pattern also underlies control of complex, unconstrained arm movements of daily activities. Six tasks were analyzed. Using kinematic data, we estimated motion of 7 degrees of freedom (DOF) of the shoulder, elbow, and wrist, and the contribution of muscle and passive interaction and gravitational torques to net torque at each joint. Despite task variety, the hand was transported predominantly by shoulder and elbow flexion/extension, although shoulder external/internal rotation also contributed in some tasks. The other DOF were used to orient the hand in space. The trailing pattern represented by production of net torque by passive torques at the shoulder or elbow or both was observed during the biggest portion of each movement. Net torque generation by muscle torque at both joints simultaneously was mainly limited to movement initiation toward the targets and movement termination when returning to the initial position, and associated with needing to overcome gravity. The results support the interpretation of previous studies that prevalence of the trailing pattern is a feature of skillful, coordinated movements. The simplicity of the trailing pattern is promising for quantification of dyscoordination caused by motor disorders and formulation of straightforward instructions to facilitate rehabilitation and motor learning.
Highlights
Motor disorders often cause dyscoordination of arm movements [1,2,3,4,5]
To establish control of each joint, we examined the role of muscle torque (MT) and PT = gravitational torque (GT) + interaction torque (IT) in the generation of Net torque (NT)
Activities of daily living, such as eating, grooming, dressing, and cooking, require the ability to perform arm movements in different directions, coordinating motion at multiple degrees of freedom (DOF) in a specific way related to each task
Summary
Motor disorders often cause dyscoordination of arm movements [1,2,3,4,5]. To understand the effect of each disorder on movement performance, normal coordination of joint motions during multi-joint movements needs to be understood. Since GT and IT depend on limb motion, this strategy consists of moving the leading joint in a way that causes passive motion at the remaining joints (through motion-dependent IT and GT) which, with modest adjustments of it by MT, results in the motion of the entire limb that accomplishes a given motor task The advantage of this control strategy is that it simplifies joint coordination. We used 6 ADL tasks: placing a cup on a shelf of 2 different heights, hair combing, bringing a cup to the mouth for drinking, turning a book page, and placing the hand on the chest like in a pledge, which is often needed during dressing We selected these tasks because they represent frequently performed daily activities and provide a variety of joint control patterns by requiring movements in different planes and directions, different involvements of the arm’s DOF, and different initial and final arm postures. To consider examples of downward movements, we included in the analysis the returning movements to the initial position
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