Triceps Surae Ia Proprioceptive Weighting in Postural Control During Quiet Stance with Vision Occlusion

<b>Background</b><b>:</b> Visual, vestibular, proprioceptive and cutaneous sensory information is important for postural control during quiet stance. When the reliability of one source of sensory information used to detect self-motion for postural 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 in postural control. The objective of this study was to determine the effect of vision occlusion on triceps surae (TS) Ia proprioceptive weighting in postural control during quiet stance, utilizing an 80 Hz muscle vibration stimulus and a quantitative measure of the body's anterior to posterior ground center of pressure (COP) response to TS muscle vibration in subjects standing freely. <b>Methods:</b> Subjects (N = 41; mean (standard deviation), 19.6(2.0) years) were examined as they stood with eyes open (EO) or eyes closed (EC). Ground COP was measured during quiet standing with and without bilateral vibration of the TS muscles. <b>Results:</b> The mean backward COP shift induced by TS vibration was significantly greater during the EC condition compared to EO (EC: -4.93(1.62) centimeters; EO: -3.21(1.33) centimeters; <i>p</i> = 6.85 × 10^-10; Cohen's d = 1.29). Thirty-seven subjects increased, and two subjects decreased their vibration-induced COP backward shift in the EC condition compared to EO, although the magnitude of the change varied. <b>Conclusions:</b> The results support the idea that, for most young subjects, there is an increased triceps surae Ia proprioceptive weighting for postural control during EC stance, possibly due to the need for postural control to depend more on non-visual feedback.