MMG and EMG responses during fatiguing isokinetic muscle contractions at different velocities.

The purpose of this study was to determine mechanomyographic (MMG) and electromyographic (EMG) responses of the superficial quadriceps muscles during repeated isokinetic contractions in order to provide information about motor control strategies during such activity, and to assess uniformity in mechanical activity (MMG) between the investigated muscles. Ten adults performed 50 maximal concentric muscle contractions at three randomly selected contraction velocities (60, 180, and 300 degrees.s(-1)) on different days. Surface electrodes and an MMG sensor were placed on the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). EMG and MMG amplitude and peak torque (PT) were calculated for each contraction, normalized, and averaged across all subjects. The results demonstrated that MMG amplitude more closely tracked the fatigue-induced decline in torque production at each velocity than did EMG amplitude. This indicates that MMG amplitude may be useful for estimating force production during fatiguing dynamic contractions when a direct measure is not available, such as during certain rehabilitative exercises. MMG amplitude responses of the VL, RF, and VM were not uniform for each velocity or across velocities, indicating that it may be possible to detect the individual contribution of each muscle to force production during repeated dynamic contractions. Therefore, MMG amplitude may be clinically useful for detecting abnormal force contributions of individual muscles during dynamic contractions, and determining whether various treatments are successful at correcting such abnormalities.