Influence of Pennation Angle and Muscle Thickness on Mechanomyographic Amplitude-Torque Relationships and Sex-Related Differences in the Vastus Lateralis.

This study examined potential sex-related differences and correlations among the pennation angle (PA), muscle thickness (MT), and mechanomyographic amplitude (MMG RMS )-torque relationships of the vastus lateralis (VL) in 11 healthy males and 12 healthy females. The PA and MT of the VL were quantified with ultrasound. Participants performed an isometric muscle action of the knee extensors that linearly increased to 70% of maximal strength followed by a 12 s plateau. MMG was recorded from the VL. Linear regression models were fit to the log-transformed MMG RMS -torque relationships to calculate b terms (slopes) for the linearly increasing segment. MMG RMS was averaged during the plateau. Males exhibited greater PA ( p < 0.001), MT ( p = 0.027), b terms ( p = 0.005), and MMG RMS ( p = 0.016). The b terms were strongly ( p < 0.001, r = 0.772) and moderately correlated ( p = 0.004, r = 0.571) with PA and MT, respectively, while MMG RMS was moderately correlated with PA ( p = 0.018, r = 0.500) and MT ( p = 0.014, r = 0.515). The greater mechanical behavior of individuals possessing a larger PA and MT of the VL may reflect increased cross-bridge activity within the muscle fibers. Additionally, PA may help explain sex-related differences in MMG RMS between sexes.