Figure 7

Attenuation of movement artifact with digital filtering. The top graph demonstrates a ten second sample of the unfiltered electromyographic (EMG) signal from the rectus femoris muscle during cycle ergometry at a power output of 230 W. The middle graph shows the corresponding unfiltered mechanomyographic (MMG) signal from the rectus femoris muscle. The bottom graph demonstrates the MMG signal from the rectus femoris muscle after digital filtering with a zero lag, fourth-order Butterworth bandpass filter with cutoff frequencies of 5 and 100 Hz. The MMG signal was detected with a contact sensor (HP 21050A) and sampled at 1,000 Hz.