| Sumario: | The purpose of this study was to use laser displacement sensors to investigate the mechanomyographic (MMG) amplitude and mean power frequency (MPF) versus isometric force relationships detected for the rectus femoris in perpendicular and transverse axes. Ten healthy men (mean ± SD age = 22.1 ± 1.6 yrs) and ten healthy women (age = 24.4 ± 2.8 yrs) performed sub-maximal to maximal isometric contractions of the dominant leg extensors. Two separate MMG signals were detected with laser displacement sensors. One MMG sensor was oriented in an axis that was perpendicular (PERP) to the muscle surface, and the second sensor was aligned transverse (TRAN) to the surface. The results indicated that MMG amplitude and MPF increased with isometric force in a similar pattern for the PERP and TRAN laser heads. The marginal mean (collapsed across force levels) MMG amplitude values were greatest for the TRAN laser head, while the PERP laser head showed the largest MPF values. Thus, these findings indicate that the measurement axis is important in determining absolute MMG amplitude and MPF values, but does not affect their patterns of response across isometric force.
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