THE ACCELERATION-VELOCITY RELATIONSHIP - IDENTIFICATION OF NORMAL ANDSPASTIC UPPER EXTREMITY MOVEMENT

This study defines and evaluates a non-invasive technique that will id entify a spasm as an uncommanded movement (U) from a normally commande d movement (C). Upper arm function during a tracking task is recognize d as non-linear and characterized by a phase plane with acceleration ( second derivative of stick position) plotted on the ordinate and veloc ity (first derivative of stick position) plotted on the abscissa. An a cceleration time constant (tau(A)) is defined as (V-A/A(M)) where A(M) is the maximal acceleration and V-A is the velocity at A(M). A decele ration time constant (tau(D)) is also defined as (V-D/D-M), where D-M is the maximal deceleration and V-D is the velocity at D-M. Ten spasti c subjects (S) were categorized into three groups of mildly spastic (M ), intermediately spastic (I), and highly spastic (H) which were compa red to five normal subjects (N). The results indicate that for C and U , both V-A and A(M) are significantly fewer for S at all three levels as compared to N. tau(A) is significantly higher for M and I as compar ed to N. Both V-D and tau(D) are significantly higher for S at all thr ee levels when compared to N. D-M is significantly lower for S at all three levels of S when compared to N. Finally, A(M) and tau(A) signifi cantly differentiate C vs U for M. V-A and tau(D) significantly differ entiate for I. V-A, A(M) as well as D-M, tau(D) significantly differen tiate far H. The physical significance of these results is discussed w ith respect to the time course and magnitude of net muscle moment (M), and the reversal of the agonist-antagonist relationship during the ac celeration and deceleration phases. Finally, a spasm identification al gorithm is proposed. (C) 1997 Elsevier Science Ltd.