Fig. 4.
Calculation of ΔF and rate modulation, where ΔF is calculated as the difference in reference unit firing frequency between test unit recruitment and test unit derecruitment (A and B, left), and rate modulation is calculated as the difference between the range of reference unit firing range. Peak reference unit firing frequency (Fmax; B, right) to the last calculated firing frequency of the reference unit (Fmin; B, right) is quantified and compared with the calculated ΔF value (Fstart − Fend; B, right) for that motor unit pair. If ΔF is within 0.5 pulses/s (pps) of the rate modulation, the pair does not meet the assumption that the reference unit is a sensitive indicator of net excitatory input to the motor neuron for the duration of the ramp contraction. The relative force production (percent maximum voluntary contraction, %MVC) that accompanies the firing rates plotted in A and B is shown in C (same for both calculations).