Differences between body movement adaptation to calf and neck muscle vibratory proprioceptive stimulation.

Adaptation is essential in maintaining stability during balance-challenging situations. We studied, in standing subjects with eyes open and closed, adaptive responses of the anteroposterior head, shoulder, hip and knee movements; gastrocnemius and tibialis anterior EMG activity and anteroposterior body posture when proprioceptive information from the neck or calf muscles underwent vibratory perturbations. After 30s of quiet stance, vibratory stimuli were applied repeatedly for 200s, and adaption to stimulation was analyzed in four successive 50s periods. Repeated neck and calf vibration significantly increased linear body movement variance at all recorded sites (p<0.001, except neck stimulation with eyes closed, EC-neck), increased tibialis anterior (p<0.001, except EC-neck) and gastrocnemious muscle activity (p<0.001). Most body movement variances and tibialis anterior EMG activity decreased significantly over time (most p-values<0.01 or lower) and overall, the body leaning forward increased from 5.5 degrees to 6.5 degrees (p<0.01). The characteristics of the responses were influenced by vision and site of vibration, e.g., neck vibration affected body posture more rapidly than calf vibration. Our findings support the notion that proprioceptive perturbations have different effects in terms of nature, degree and adaptive response depending on site of vibratory proprioceptive stimulation, a factor that needs consideration in clinical investigations and design of rehabilitation programs.