DECOMPOSITION-ENHANCED SPIKE-TRIGGERED AVERAGING - CONTRACTION LEVEL EFFECTS

Decomposition-enhanced spike-triggered averaging (DE-STA) was applied to the vastus medialis muscle to examine size distributions of surface -detected motor unit action potentials (S-MUAPs) at Various force leve ls, Using DE-STA, 15-20 S-MUAPs were identified during 5%, 10%, 20%, a nd 30% of maximum voluntary contraction. Average S-MUAPs showed increa se in peak to peak (and negative peak) amplitude with force (in mu V): 5% = 37.9 +/- 6.1 (16.6 +/- 2.5), 10% = 44.0 +/- 4.0 (20.4 +/- 1.8), 20% = 80.7 +/- 9.3 (41.3 +/- 4.5), and 30% = 102.5 +/- 10.3 (53.6 +/- 5.0), Test-retest variability of peak to peak (and negative peak ampli tude) between repeated trials was 0.10 (0.14), 0.14 (0.14), 0.17 (0.15 ), and 0.21 (0.20) at 5%, 10%, 20%, and 30% respectively. A relationsh ip was found between the S-MUAP amplitude and force (r(2) = 0.78, df = 90, F = 160, P < 0.001). Increase in average S-MUAP amplitude with fo rce suggests that STA performed only al low levels of contraction may result in a biased sampling and small average S-MUAP amplitudes. (C) 1 997 John Wiley & Sons, Inc.