Table 3.

Modeled Boltzmann parameters for vastus lateralis , rectus femoris and vastus medialis muscles

		Vastus lateralis	Rectus femoris	Vastus medialis
MEPmax · Mmax -1
	10% MVC	34.7 ± 21.6	68.8 ± 19.6*,#	42.7 ± 22.3
	20% MVC	42.9 ± 17.1	83.3 ± 19.3	51.2 ± 18.7
	50% MVC	42.6 ± 11.1	83.0 ± 23.0	47.7 ± 11.9
S 50
	10% MVC	43 ± 10**,##	45 ± 11**,##	44 ± 10**,##
	20% MVC	38 ± 11**	40 ± 10**	39 ± 10**
	50% MVC	32 ± 9	30 ± 7	34 ± 7
k
	10% MVC	0.051 ± 0.018**,#	0.036 ± 0.029	0.037 ± 0.018
	20% MVC	0.032 ± 0.020	0.027 ± 0.015	0.031 ± 0.026
	50% MVC	0.020 ± 0.018	0.019 ± 0.014	0.027 ± 0.012
r 2
	10% MVC
	Model	0.928 ± 0.045†	0.964 ± 0.051‡	0.937 ± 0.045‡
	Linear regression	0.804 ± 0.095	0.770 ± 0.118	0.779 ± 0.112
	20% MVC
	Model	0.943 ± 0.048†	0.982 ± 0.012‡	0.933 ± 0.050‡
	Linear regression	0.724 ± 0.173	0.716 ± 0.180	0.688 ± 0.196
	50% MVC
	Model	0.919 ± 0.052‡	0.900 ± 0.092‡	0.882 ± 0.115‡
	Linear regression	0.563 ± 0.214	0.537 ± 0.207	0.598 ± 0.190

MEPmax · Mmax^-1: maximal motor-evoked potential amplitude (MEPmax) normalized to maximal M-wave amplitude, MVC: maximal voluntary force, S50: stimulus intensity to evoke motor-evoked potentials half the amplitude of MEPmax (as % maximal stimulator output), k: slope parameter (inversely proportional to maximal function steepness), r²: coefficient of determination. Values are expressed as means ± standard deviation. Significantly different from 50% maximal voluntary force (MVC), * (p < 0.05) and ** (p < 0.01); significantly different from 20% MVC, # (p < 0.05) and ## (p < 0.01); significantly different from linear relationship, † (p < 0.05) and ‡ (p < 0.01).