Triceps Surae Muscle Ia Proprioceptive Weighting During Quiet Stance with Vision Occlusion

Visual, vestibular, proprioceptive and cutaneous sensory information is important for posture control during quiet stance. When the reliability of one source of sensory information used to detect self-motion for posture control is reduced, there may be a reweighting of inputs within and/or across the remaining sensory systems determining self-motion for postural control. Muscle vibration, which creates an illusion of muscle stretch and a compensatory movement to shorten the vibrated muscle, may be used to determine the weighting of muscle spindle Ia proprioception for posture control. The objective of this study was to determine the effect of vision occlusion on triceps surae muscle Ia proprioceptive weighting for postural control during quiet stance, utilizing 80 Hz muscle vibration and a quantitative measure of the bodys anterior to posterior ground center of pressure response to triceps surae muscle vibration in freely standing subjects. Subjects (N = 41; mean(standard deviation), 19.6(2.0) years) were examined as they stood with eyes open or eyes closed. Ground center of pressure was measured during quiet standing with, and without, bilateral vibration of the triceps surae muscles. The mean backward center of pressure shift induced by triceps surae vibration was significantly greater during the eyes closed condition compared to eyes open (eyes closed: -4.93(1.62) centimeters; eyes open: -3.21(1.33) centimeters; p = 6.85E-10; Cohens d = 1.29). Thirty-seven subjects increased, and two subjects decreased, their vibration induced center of pressure backward shift in the eyes closed condition compared to eyes open, although the magnitude of the change varied. Results support the idea that for most subjects, during an eyes closed stance there is an increased triceps surae muscle Ia proprioceptive weighting for postural control, due to the need for posture control to depend more on non-visual feedback.