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Contribution of load and length related manipulations to muscle responses during force perturbations Klarner, Taryn

Abstract

Adding resistance to the legs during walking increases swing phase muscle activity, presumably through load-sensitive flexor muscle feedback pathways. However, increased muscle activity could also be due to the changes in lower limb kinematics that accompany resistance. Thus, the purpose of this study is to evaluate the contribution of resistance and knee pattern manipulations to muscle responses during force perturbations. The natural kinematic pattern associated with resistance was determined as subjects walked with the Lokomat applying resistances of 0%, 5% and 10% of their maximum voluntary contraction (MVC) to the hip and knee joints of both legs. Walking with increased resistance causes decreased knee flexion during the swing phase and decreased stride frequency. Knee joint data and stride frequencies at these resistance levels were used to create three biofeedback traces, representing three different knee pattern conditions, to be used in the experimental block. Subjects then walked at 9 different combinations of resistance (0%, 5% and 10% MVC) and knee pattern (fast, medium and slow). Leg muscle activity and joint kinematics were recorded and analyzed. Results indicate that both resistance and knee pattern perturbations independently contribute to ongoing swing phase activity in the quadriceps. Analysis of effect sizes indicate that resistance contributes more than the knee pattern manipulation to quadriceps muscle activity. Information arising from both load sensitive and length sensitive afferents could be involved in mediating these responses.

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