Repetitive trunk loading leads to faster trunk movement in response to external perturbation

The purpose of the present study was to examine trunk movement pattern responses to mechanical perturbation before and after two different repetitive trunk flexion-extension loading schemes. Spatial and temporal parameters were studied to understand the trunk recovery from an anteriorly directed perturbation. Eighteen male and female subjects (18-27 yrs) participated in active and passive trunk flexion-extension, performed seven days apart. Subjects performed 60 trunk flexion-extension repetitions in each condition. Subjects either volitionally moved their trunks (active condition) or relaxed while a dynamometer controlled the movements (passive condition). Trunk perturbations occurred before and immediately after two 30 repetition sessions. Initial responses included latency measures of trunk displacement and peak trunk velocity (V_P). Temporal measures included perturbation onset to initial trunk movement (T_D), movement initiation to V_P (T_MIPV), and perturbation onset to V_P (T_PPV). Recovery measures included peak recovery velocity (V_PR), recovery time (T_R), velocity slope (V_S), and recovery slope (R_S). Differences between loading sessions were present for T_PPV (p < .05), T_R (p < .05), and R_S (p < .05). Overall, the results indicate repetitive loading leads to lower resistance to perturbation, but faster recovery from perturbation although no differences to active or passive repetitive loading was observed.