Fig. 5.

Motor unit discharge characteristics during the steady contraction when supporting a mass with the elbow flexor muscles. A and B: mean discharge rate for 20 motor units from old adults (A) and 20 motor units from young adults (B) for the small and large differences between target force and recruitment threshold force [%maximal voluntary contractions (MVC)] for each 20% epoch of discharge duration. C and D: CV for the first 5 ISIs recorded at the beginning of each 20% epoch during the sustained contraction for old (C) and young (D) adults.