Fig. 2.

Sample data from a young subject. Motor unit recruitment was defined as the force at which a motor unit began discharging action potentials repetitively. Recruitment threshold was determined by moving a 0.5-s window forward in time in 1-ms increments through the data until the coefficient of variation (CV) for interspike interval within the window was < 50%. The force corresponding to the first discharge within this window was taken as the recruitment threshold force. Derecruitment threshold force was obtained with the same algorithm, except the last discharge within the window was taken as the derecruitment threshold force. SMU, single motor unit; MVC, maximal voluntary contraction; pps, pulses per second.