Comparing the reliability of voluntary and evoked muscle actions

The purpose of this exploratory study was to quantify the test-retest reliability, intertrial variability and correlations between variables calculated during voluntary and evoked muscle actions.

During three separate trials of isometric leg extension muscle actions with 14 men [mean age (± SD) = 21.9 (± 3.2) years; height = 179.2 (± 8.0) cm; mass = 77.7 (± 10.9) kg], peak torque (PT(V)), time to peak torque (TPT(V)), rate of torque development (RTD(V)), time to peak rate of torque development (TRTD(V)), electromechanical delay (EMD(V)) and EMG amplitude (EMG(RMS)) were quantified for voluntary muscle actions. Peak twitch torque (PTE ), time to peak twitch torque (TPT(E)), rate of torque development (RTD(E)), time to peak rate of torque development (TRTD(E)), electromechanical delay (EMD(E)), peak-to-peak M-wave (Mp-p) and M-wave area (M(area)) were calculated for evoked twitches. All electromyographic measurements were recorded over the vastus lateralis.

Voluntary intraclass correlation coefficients (ICC) were 0.84-0.96, except for TRTD(V) (0.30) and EMD(V) (0.74). Evoked ICC were 0.80-0.95, except for EMD(E) (0.52). Relative standard errors of measurement for TPT and TRT(D) were greater for voluntary than evoked, whereas the value for PTE was greater than PT(V). There were low to moderate correlations (r = -0.41-0.51) between common voluntary and evoked variables.

Evoked variables showed lower intertrial variability than voluntary. Overall, voluntary and evoked muscle actions provide unique, complimentary information regarding neuromuscular function that cannot be used interchangeably.