Electromyographic, but not mechanomyographic amplitude-force relationships, distinguished differences in voluntary...

The purpose of the present study was to examine the influence of activation capabilities on the electromyography (EMGRMS) and mechanomyography amplitude (MMGRMS)-force relationships of the vastus lateralis (VL) and rectus femoris (RF). Thirteen men (mean±SD; age=22±3 year) performed nine submaximal contractions (10-90% maximal voluntary contraction [MVC]) with the interpolated twitch technique performed during a separate contraction at 90% MVC to calculate percent voluntary activation (%VA). Nine participants with >90% VA were categorized into the high-activated group with the remaining categorized into the moderate-activated group. Slopes (b terms) were calculated from the log-transformed EMGRMS and MMGRMS-force relationships. The b terms (collapsed across the VL and RF) for the EMGRMS-force relationships were greater for the high- (1.29±0.31) than the moderate-activated (1.10±0.20) group. In contrast, there were no differences in the b terms for the MMGRMS-force relationships between the high- and moderate-activated groups. For the EMGRMS and MMGRMS-force relationships, the b terms were greater for the RF (1.38±0.30, 0.81±0.20) than the VL (1.08±0.19, 0.60±0.13) collapsed across groups. The b terms from the EMGRMS-force relationships, but not the MMGRMS-force relationships, reflected differences in %VA.