Mechanomyographic and electromyographic responses during submaximal cycle ergometry

The purpose of this study was to examine the mechanomyographic (MMG) and electromyographic (EMG) responses during continuous, cycle ergometer workbouts performed at constant power outputs. Eight adults [mean (SD) age, 21.5 (1.6) years] volunteered to perform an incremental test to exhaustion for the determination of peak power ((W) over dot (peak)) and four, 15-min (or to exhaustion) rides at constant power outputs of 50%, 65%, 80%, and 95% (W) over dot (peak). Piezoelectric crystal contact sensors were placed on the vastus lateralis (VL) and vastus medialis (VM) muscles to record the MMG signals. Bipolar surface electrode arrangements were placed on the VL and VM to record the EMG signals. Five-second samples of the MMG and EMG signals were recorded every 30 s at power outputs of 50%, 65%, and 80 % (W) over dot (peak), and every 15 s at 95% (W) over dot (peak). The amplitudes of the selected portions of the signals were normalized to the first values recorded during the continuous rides, and regression analyses were used to determine whether the slope coefficients for the MMG and EMG versus time relationships were significantly (P < 0.05) different from zero. The results indicate that EMG amplitude increased (range of slope coefficients: 0.03-0.56) during the continuous rides for both muscles at all four power outputs (except the VM at 50% (W) over dot (peak)), while MMG amplitude increased (slope coefficient at 95% (W) over dot (peak) for VM = 0.19), decreased (range of slope coefficients for VL and VM at 50% and 65% (W) over dot (peak) = -0.14 to -0.24), or remained unchanged (range of slope coefficients for VL and VM at 80% (W) over dot (peak) and VL at 95% (W) over dot (peak) = -0.06 to 0.12) depending on the power output. The patterns of the MMG responses, however, were similar for the VL and VM muscles, except at 95% (W) over dot (peak). Fatigue-induced changes in motor-unit recruitment and discharge rates, or muscular compliance may explain the differences between power outputs in the patterns of the MMG amplitude responses.