System identification of human ankle dynamics: intersubject variability and intrasubject reliability.

Intersubject variability and intrasubject reliability of quantitative measures of normal human ankle mechanics were examined in fifteen young adults. Each subject was examined on two occasions to characterize passive joint dynamics, in terms of the position-stiffness relation, and active joint dynamics, in terms of the torque-stiffness relation. Quantitative, objective measures of joint properties corresponding to those in clinical use were also made for comparison purposes. Results demonstrated that measures of passive and active joint dynamics generally had an intrasubject reliability which was as good as or better than most clinical measures. Intersubject variability was somewhat larger as is the case for the clinical measures.