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 = 0.38).  Limits of Stability variables were positively correlated (reaction time and maximum excursion range r_s: 0.585 – 0.846; directional control and mean velocity range r_s: 0.307 – 0.472).  Muscular reaction times correlated weakly with those from center of pressure (mean r_s prosthesis users – 0.186 and controls –  0.101). 

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.