Electromyographic latency changes in the ankle musculature during inversion moments.

Ten uninjured subjects (ages 18 to 30 years) had electromyographic testing of the peroneus longus, peroneus brevis, and tibialis anterior muscles in response to inversion moments at two speeds (50 and 200 deg/sec) and two joint angles (neutral and 20 degrees of plantar flexion) using a hydraulically controlled tilt platform. Subjects underwent 10 trials of each type of inversion moment on Day 1 testing, which included 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 testing. Repeatability was assessed by comparing Day 1 with Day 2 data. The latency measurements (the time between the beginning of the inversion moment and the onset of first motor response) for the peroneus brevis and tibialis anterior muscles were found to be reliable and repeatable 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 plantar flexion angle both caused significant changes in latency response of the peroneus muscles, with increased speed producing a shorter latency response and increased angle causing a longer latency response. Our results indicate a loss of protective reflexes with increasing plantar flexion.