Effect of mechanomyography as a biofeedback method to enhance muscle relaxation and performance

The purpose of the study was to examine the potential for using the mechanomyographic (MMG) signal as a biofeedback method to enhance muscular relaxation and to improve performance during forearm flexion repetitions to fatigue. Twelve adult (mean +/- SD; age: 22.0 +/- 1.1 years) moderately trained subjects (weight: 82.3 +/- 29.2 kg; height: 165.7 +/- 49.0 cm) were instructed to relax the biceps brachii muscle using MMG biofeedback (BIO) provided by viewing a computer screen graphically displaying the MMG signal and then without using MMG biofeedback (NOBIO). Electromyographic (EMG) and MMG signals were detected midway over the biceps brachii during the relaxation protocol. In subsequent visits to the laboratory, subjects performed as many repetitions as possible at 85% of 1 repetition maximum with BIO and NOBIO using the seated preacher curl exercise. Two-way (biofeedback x gender) mixed factorial analyses of variance revealed significantly (p < 0.05) lower MMG (mean +/- SEM; BIO = 0.6 +/- 0.1 mV; NOBIO = 1.1 +/- 0.2 mV) and EMG amplitudes (BIO = 6.6 +/- 0.6 microV; NOBIO = 9.4 +/- 1.4 microV) for BIO when subjects were instructed to relax the biceps brachii muscle. There was no significant difference in the number of forearm flexion repetitions performed for BIO (mean +/- SD; 7.9 +/- 0.4 reps) vs. NOBIO (8.1 +/- 0.6 reps). The results of the present study revealed that using MMG as a biofeedback technique can enhance the development of muscle relaxation, but is not useful in delaying fatigue during forearm flexion repetitions. Our results may have been influenced by a relatively short training phase designed to teach subjects to use the MMG signal as a biofeedback method. Future studies are needed to determine whether MMG biofeedback can be used for other purposes. If MMG is found to be useful as a biofeedback method, it has some distinct practical advantages over EMG that the strength and conditioning athlete and professional may find appealing.