Table 2.
MU discharge parameters of the ST muscle
| Parameter | Young | Old | ||||
|---|---|---|---|---|---|---|
| Targeted contraction, %MVC | 25 | 50 | 100 | 25 | 50 | 100 |
| Voluntary contraction, %MVC | 24 ± 2 | 49 ± 3 | 94 ± 2 | 26 ± 3 | 49 ± 4 | 94 ± 2 |
| MU discharges, Hz | 20.2 ± 2.4 | 27.0 ± 3.5 | 47.2 ± 9.6 | 13.4 ± 2.0* | 17.6 ± 3.0* | 26.7 ± 5.8* |
| Total number MUPTs | 558 | 489 | 310 | 376 | 447 | 283 |
| MUPTs/participant | 56 ± 12 | 49 ± 17 | 31 ± 14 | 38 ± 11 | 45 ± 11 | 28 ± 10 |
| Number of ISI | 13 ± 4 | 11 ± 3 | 9 ± 2 | 13 ± 4 | 12 ± 3 | 9 ± 2 |
| Coefficient of variation | 12.1 ± 1.4 | 13.2 ± 0.7 | 14.6 ± 1.4 | 12.0 ± 1.6 | 13.0 ± 1.5 | 14.5 ± 1.2 |
Values are presented as the ensemble means ± SD; n = 20. Motor unit (MU) potential trains (MUPTs) were recorded during left superior trapezius (ST) submaximal [25 and 50% maximal voluntary isometric contraction (MVC)] and MVC intensities. ISI, interspike interval.
*
P < 0.001, between age groups (young vs. old) comparing the same targeted MVC.