ELECTROMYOGRAPHIC LATENCY CHANGES IN THE ANKLE MUSCULATURE DURING INVERSION MOMENTS

Ten uninjured subjects (ages 18 to 30 years) had electromyographic tes ting of the peroneus longus, peroneus brevis, and tibialis anterior mu scles in response to inversion moments at two speeds (50 and 200 deg/s ec) and two joint angles (neutral and 20 degrees of plantar flexion) u sing a hydraulically controlled tilt platform. Subjects underwent 10 t rials of each type of inversion moment on Day 1 testing, which include d both legs. On Day 2, subjects again underwent 10 trials of each type of inversion moment, but only on one leg. Reliability was assessed by comparing left and right leg data within muscle groups for Day 1 test ing. Repeatability was assessed by comparing Day 1 with Day 2 data. Th e latency measurements (the time between the beginning of the inversio n moment and the onset of first motor response) for the peroneus brevi s and tibialis anterior muscles were found to be reliable and repeatab le with no significant differences between the same muscle groups. The peroneus longus muscle had a significant difference between legs but was found to be highly repeatable. Speed of inversion moment and plant ar flexion angle both caused significant changes in latency response o f the peroneus muscles, with increased speed producing a shorter laten cy response and increased angle causing a longer latency response. Our results indicate a loss of protective reflexes with increasing planta r flexion.