Fig. 7.

Average value of k′ plotted against estimates of motor neuron number (MNN). Data were fit (R² = 0.90, P = 0.001) with the following inverse function: k′ = 1.06 + (1/0.0085 × MNN). MNNs were obtained from three different sources: 1) retrograde labeling of motor neurons in the monkey [ECU: 216 and BB: 1,051 (Jenny and Inukai, 1983)], 2) motor axon counts from a human cadaver [3DI: 119 from the first dorsal interosseus, BR: 333, LG: 579 from the medial gastrocnemius, and TA: 445 (Feinstein et al. 1955)], and 3) presumed unitary increments in evoked EMG responses [AH: 73 based on an original estimate of 43 (Johns and Fuglevand 2011) multiplied by 1.7 (David et al. 2010)]. Overall, there was an inverse relation between synchrony magnitude and number of motor neurons innervating a muscle.