Tactile stimulation restores inhibited stretch reflex attributable to attenuation of la afferents during surprise landing

Abstract

Purpose: Arthrogenic muscle inhibition(AMI) is induced by pathological knee conditions. The present study aimed to investigate the effect of tactile stimulation on reflex changes induced by simulated AMI during unpredictable landing performances. Methods: Twenty participants performed six unilateral landing tasks: 15cm normal landing (15NL), 30cm normal landing(30NL), surprise landing(SL), 30cm normal landing following vibration (30NLV), surprise landing following vibration(SLV), and surprise landing following vibration with Kinesiology-tape(SLK). For the surprise landing tasks, the solid landing platform(15cm) was removed and replaced by a false plate platform. Since the false plate dislodged easily under load, participants unpredictably fell through the plate to the actual landing surface 15cm below. After completing 15NL, 30NL, SL, vibration stimulation was applied to participants' knees to induce neurological changes similar to AMI. After vibration stimulation, participants performed 30NLV, SLV and SLK in a random order. EMG in the post-landing short latency(31-60 ms) and medium latency(61-90 ms) periods were examined. EMG signals from the vastus lateralis(VL), vastus medialis(VM), and lateral hamstrings(LH) were recorded and compared between tasks. Results: EMG of all muscles were significantly enhanced in the medium latency period. Enhanced EMG were suppressed by vibration stimulation in the VL, but the suppressed EMG were restored after cutaneous stimulation(p<0.01). Conclusion: Our findings suggest that AMI could alter motor control patterns during unpredictable landing, and that tactile stimulation could restore the altered motor control to a normal state. The use of tactile stimulation may help maintain normal motor control patterns in injured individuals.