Table 1.

Model parameters

Models	Parameters	Varied	Values
Neural	Range of recruitment threshold	Yes	30, 5
	Minimum firing rate	No	8 Hz
	Excitatory drive-firing rate gain	No	1
	Peak firing rate for first motor unit	No	45 Hz
	Peak firing rate difference	No	10 Hz
	Coefficient of variation in inter-spike interval	No	0.2
	Synchronization: fraction of reference spikes	Yes	0, 0.061
	Synchronization: fraction of test units	Yes	0, 0.061
Muscle	Range of peak forces	No	100
	Longest contraction time	No	90 ms
	Range of contraction times	No	3
EMG	Surface-recorded action potential duration	Yes	5, 20 ms
	Surface-recorded action potential magnitude	Yes	All equal, proportional to peak force

The nominal parameter set is shown in bold. The sensitivity of the model to each of the varied parameters was examined by changing that parameter alone while keeping the other parameters at their nominal value.