Unexpected walking perturbations: Reliability and validity of a new treadmill protocol to provoke muscular reflex activities at lower extremities and the trunk

Instrumented treadmills offer the potential to generate standardized walking perturbations, which are particularly rapid and powerful. However, technical requirements to release adequate perturbations regarding timing, duration and amplitude are demanding. This study investigated the test-retest reliability and validity of a new treadmill perturbation protocol releasing rapid and unexpected belt perturbations to provoke muscular reflex responses at lower extremities and the trunk. Fourteen healthy participants underwent two identical treadmill walking protocols, consisting of 10 superimposed one-sided belt perturbations (100 ms duration; 2 m/s amplitude), triggered by a plantar pressure insole 200 ms after heel contact. Delay, duration and amplitude of applied perturbations were recorded by 3D-motion capture. Muscular reflex responses (within 200 ms) were measured at lower extremities and the trunk (10-lead EMG). Data was analyzed descriptively (mean ± SD). Reliability was analyzed using test-retest variability (TRV%) and limits of agreement (LoA, bias ± 1.96∗SD). Perturbation delay was 202 ± 14 ms, duration was 102 ± 4 ms and amplitude was 2.1 ± 0.01 m/s. TRV for perturbation delay, duration and amplitude ranged from 5.0% to 5.7%. LoA reached 3 ± 36 ms for delay, 2 ± 13 ms for duration and 0.0 ± 0.3 m/s for amplitude. EMG amplitudes following perturbations ranged between 106 ± 97% and 909 ± 979% of unperturbed gait and EMG latencies between 82 ± 14 ms and 106 ± 16 ms. Minor differences between preset and observed perturbation characteristics and results of test-retest analysis prove a high validity with excellent reliability of the setup. Therefore, the protocol tested can be recommended to provoke muscular reflex responses at lower extremities and the trunk in perturbed walking.