TABLE 1.

Motor unit characteristics before the sustained contraction

Force TaskPosition Task
RT < Target ForceRT > Target ForceRT < Target ForceRT > Target Force
Recruitment characteristics
    Number of MU14161316
    Force threshold, % MVC11.7 ± 2.331.8 ± 2.19.8 ± 2.432.0 ± 2.1
    Range of recruitment, % MVC3–1516–496–1516–56
    Discharge rate, pps14.5 ± 5.716.7 ± 2.715.4 ± 2.815.2 ± 1.9
    CV for ISI, %19.6 ± 9.625.2 ± 9.418.9 ± 8.726.0 ± 8.7
Derecruitment characteristics
    Number of MU7868
    Force threshold, % MVC16.2 ± 5.838.7 ± 14.312.8 ± 7.434.7 ± 14.9
    Range of derecruitment, % MVC12–1817–498–2027–56
    Discharge rate, pps13.0 ± 1.912.0 ± 1.512.8 ± 3.911.5 ± 1.8
    CV for ISI, %29.9 ± 6.934.9 ± 14.030.2 ± 12.038.3 ± 11.9
  • The RT differed between motor units that were activated below and above the target force in both tasks (P = 0.0001). The mean discharge rate and the CV for ISI were calculated from 1st 4 interspike intervals at recruitment and the last 4 interspike intervals at derecruitment. The discharge rate variability at recruitment differed significantly between the 2 groups of motor units (recruitment threshold main effect, P = 0.015). Values are expressed as mean ± SD, except for the discharge rate expressed as mean ± 95% CI. RT, recruitment threshold; MU, motor unit; MVC, maximal voluntary contraction; ISI, interspike interval.