The validity of forceplate data as a measure of rapid and targeted volitional movements of the centre of mass in transtibial prosthesis users.

PURPOSE: To validate outcome variables from the limits of stability protocol that are derived from the center of pressure with those same variables derived from the center of mass during rapid, volitional responses in transtibial prosthesis users.

METHOD: Prosthesis users (n = 21) and matched controls (n = 21) executed movements while force and motion data were collected. Correlation coefficients were used to investigate relationships between center of pressure and center of mass for: x/y coordinates positions, limits of stability outcome variables and muscular reaction times.

RESULTS: Significant differences were seen in correlation between x/y coordinate positions toward the intact limb (mean effect size of differences: r = .38). Limits of stability variables were positively correlated (reaction time and maximum excursion range rs : .585-.846; directional control and mean velocity range rs : .307-.472). Muscular reaction times correlated weakly with those from center of pressure (mean rs prosthesis users: .186 and controls: .101).

CONCLUSIONS: Forceplate measures are valid in describing rapid, volitional movements in unilateral transtibial prosthesis users. Limits of stability outcomes extracted from center of pressure and center of mass are highly correlated, but can be sensitive to direction. Muscular reaction time correlates very little with reaction times extracted from the other variables. Implications for rehabilitation Rehabilitation programs utilizing limits of stability are valid measures of postural control in transtibial prosthesis users. Clinicians interpreting the outcomes from limits of stability need to be aware of their varying validity. Muscular reaction times correlate weakly with other measures of reaction time, highlighting the complexity of rapidly coordinating volitional movements in prosthesis users.