Repetitive Trunk Loading Leads to Faster Trunk Movement in Response to External Perturbation

PURPOSE: The purpose of this study was to examine the responses of trunk movement patterns to mechanical perturbation before and after two different repetitive trunk flexion-extension loading schemes. Spatial and temporal biomechanical parameters were studied to further understand the ability of the trunk to recover from anterior directed perturbations. METHODS: Eighteen male (n=9) and female (n=9) participants (21.7 ± 2.3 yrs, 1.75 ± 0.08 m, 72.5 ± 12.0 kg) were recruited. They participated in active and passive trunk flexion-extension loading, performed at least 7 days apart. Participants performed 60 trunk flexion-extension repetitions in each condition. Participants either volitionally moved their trunks (active condition) or relaxed during dynamometer controlled movements (passive condition). Trunk perturbations occurred before and immediately after two 30-repetition sessions. Temporal measures included perturbation onset to initial trunk movement (TD), movement initiation to peak trunk velocity (VP) (TMIPV), and perturbation onset to VP (TPPV). Recovery measures included peak recovery velocity (VPR), recovery time (TR), velocity slope (VS), and recovery slope (RS). Repeated measures ANOVA was used to analyze the data. Alpha level was set at 0.05. RESULTS: There was no sex by session interaction observed. Significant sex differences were present for TMIPV (Male 112.4 ± 74.6 ms, Female 96.5 ± 44.6 ms, p \u3c 0.02), VPR (Male -12.0 ± 8.6 deg/s, Female -15.6 ±13.0 deg/s, p \u3c 0.01), and VS (Male -273.3 ± 215.9 deg/s/s, Female -332.4 ± 363.8 deg/s/s, p \u3c 0.05) measures. Differences between loading sessions were present for TPPV (Block1: 212.8 ± 239.6, Block2: 168.3 ± 46.7, Block3: 171.7 ± 82.1 ms, p \u3c 0.039), and RS (Block1: -6.65 ± 5.6, Block2: -4.76 ± 3.7, Block 3: -5.28 ± 5.2, p \u3c 0.02). CONCLUSIONS: Distinct sex and time-dependent modifications to the kinematics parameters are attributed to the altered mechanical behavior of the lumbar tissues as well as volitional loading by the trunk extensors. Overall, results indicate repetitive loading leads to lower resistance to perturbation, but faster recovery from perturbation although no differences to active or passive repetitive loading were observed