Habituation during repeated exposure to balance recovery from a forward loss of balance in younger adults
Whitten, Justin Mark Moeller
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The purpose of this study was to begin to develop within session volume parameters for perturbation-based balance training by determining the minimum number of exposures needed for participants to habituate to balance recovery from a substantial perturbation. Two young adult participants were exposed to 15 substantial perturbations induced via release from a static forward lean. All participants were instructed to attempt to recover balance by taking a single rapid step. A scalable anatomical model consisting of 36 degrees-of-freedom and 94 muscle actuators was used to compute kinematics and joint moments from motion capture and force plate data. Margin of stability was calculated at heel strike and maximum knee joint flexion to quantify balance recovery performance. Balance recovery trials were divided in to three blocks (early, middle, and late) with 5 trials in each block and static optimization was used to compute estimates of the mean and peak force generated by key muscle groups during recovery for each block. Participant margin of stability declined rapidly during early balance recovery trials and plateaued between trials 5-8. Hip abductor forces remained relatively consistent across trials while the force produced by the Vastus Femoris group decreased during the mid and late trial blocks. Mean force produced by the Soleus during balance recovery decreased across trial blocks. In contrast, the peak force and impulse generated by the Soleus increased across trial blocks. We interpret these data to reflect an adaptation in balance recovery coordination strategy, which appears to occur sometime between the early and middle trial blocks and stems from young participants desire to minimize the effort associated with successful recovery of balance. These results further suggest participants became habituated to balance recovery after exposure to 5-8 substantial perturbations.