The acceleration time constant: comparison of normal and spastic upper extremity movement

Upper arm function during a tracking task is recognized as non-linear and characterized by a phase plane with acceleration (second derivative of stick position) plotted on the ordinate and velocity (first derivative of stick position) plotted on the abscissa. An acceleration time constant (τ_A) is defined as [V_A /A_M] where V_A is the velocity at maximal acceleration and AM is the actual maximal acceleration. Ten spastic subjects (S) were categorized into 3 groups of mildly spastic (M), intermediately spastic (I), and highly spastic (H) which were compared to 5 normal subjects (N). When performing a commanded movement, T_A is a significant identifier between M, I and H. Specifically, T _A for M is highest, T_A for I is intermediate, and τ_A for H is lowest. There is no significant difference between τ_A for H and τ_A for N. The physical significance of these results is discussed