Effects of tibialis anterior muscle vibration on quiet stance

Abstract

Understanding the context in which vibration of musculature about the ankle joints elicits postural sway is important if it is to be utilized as a means of manipulating postural control for therapeutic or training purposes. The purpose of this study was to observe if the postural response associated with the vibration of the tibialis anterior (TA) muscles would remain intact despite multiple exposures during a series of forward and backward translating perturbations. Twenty young healthy adults (18-35 years old) were asked to maintain an upright erect posture on a forceplate with their eyes closed during two separate trials of quiet stance both without (preNV) and with (preVib) TA muscle vibration being applied. Subjects were then exposed to 60 bouts of forward and backwards translating perturbations of various amplitudes with TA vibration being applied during 30 of the perturbations, after which another trial of quiet stance with TA vibration (postVib) was taken. Anterior-posterior center of pressure (COP) and shear force measurements were used to calculate root-mean-square (RMS) of the sway, mean power frequency (MPF), shift from zero, and strategy score percentages as dependent variables. Of interest here are the postural responses obtained during the quiet stance conditions. A one-way ANOVA with Tukey's HSD post-hoc tests were used to compare means of the three quiet stance conditions for each of the dependent variables. Non-significant MPF results revealed no change in sway frequency oscillations due to vibration throughout the study. RMS sway was significantly greater for preVib and postVib trials than preNV, and strategy scores were significantly lower for preVib and postVib than preNV, indicating greater shear forces with the vibration conditions. No significant differences between preVib and postVib means were observed in any of the COP measures. This indicates that adaptation to the TA muscle vibration response did not occur and suggests that the distorted input associated with vibration was not fully down weighted by the sensory motor system during quiet upright stance, despite repeated exposure to vibration throughout the testing protocol.