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Objective To study the characteristics of neural adaptation for resistance training of maximum voluntary contraction (MVC) of muscles at different joint angles. Methods Thirty healthy male college students were randomly divided into 3 groups, and each group was subjected to MVC isometric contraction resistance training at elbow joint angles of 45°, 90°, and 135°. Surface electromyography (sEMG) signals of the biceps brachii were measured before and after training, and the root mean square (RMS) and median frequency (MF) of the sEMG signals were also analyzed. ResultsThere were significant differences in normalized RMS of sEMG for the biceps brachii before and after training at 45°, 90°, and 135° elbow joints. Comparison of the RMS between different angles after training showed that 45° was significantly different from 90° and 135°. There were no significant differences between 90° and 135°. After training, no significant differences were found in normalized MF at all angles. Conclusions The RMS of sEMG shows angle-specific changes, while the MF of sEMG does not have angle-specific changes. When the biceps brachii is at the middle and large elbow joint angles, the neural adaptation effect produced by isometric resistance training is better.
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Objective To investigate the extent of cross-education between the pronation and supination muscles of the right and left forearms after unilateral isometric training.Methods Twenty healthy young girls were randomized into a training group and a control group using a random number table.The training group underwent isometric training of their right forearms for six weeks,while the control group continued ordinary life without exercises.Pronation peak torque (PPT) and supination peak torque (SPT) were assessed before and after the training for both groups.Results The differences in PPT or SPT between the training group and the control group were not significant before the training program.When the training had been completed,however,the average PPT and SPT on right side of those trained of course had increased significantly compared to before training or to the control group.More significantly,the average PPT and SPT on the left side in the training group were also significantly better than before training or in the control group after training.Conclusion Unilateral isometric training of the forearm pronation and supination muscles for six weeks can significantly increase muscle strength bilaterally,indicating good cross-education.
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We studied the mechanism for slowing surface electromyography (EMG) during fatiguing contraction using superimposed M-wave analysis. Seven healthy male subjects exerted 60% maximum voluntary contraction of isometric abductions in the left first dorsal interosseous muscle (FDI) until exhaustion. Simultaneously with voluntary contractions, the ulnar nerve was electrically stimulated at supramaximal intensity, and volitional EMG and superimposed M-waves were obtained. We examined the behavior of muscle fiber conduction velocity (MFCV) and median frequency (MDF) for both EMG, with the following results:<BR>1) MFCV calculated from volitional EMG of FDI was about 6 m/s during 60% MVC.<BR>2) The waveform of voluntary EMG detected from FDI slowed in all subjects during fatiguing contraction at 60% MVC, indicating fatigue had developed in the muscle.<BR>3) As fatigue progressed, the waveform of the superimposed M-wave tended to decrease in amplitude and increase in duration.<BR>4) As fatigue progressed, MDF and MFCV in volitional EMG decreased significantly (p<0.04) . The rate of change was larger in MDF than in MFCV (p<0.01) .<BR>5) As fatigue progressed, MDF and MFCV in the superimposed M-wave decreased significantly (p<0.01) . The rate of change was larger in NIDF than in MFCV (p<0.05) .<BR>These results suggested that MFCV and other peripheral factors affected the slowing of volitional EMG. Elongation of the depolarization zone in muscle fiber is proposed as a peripheral factor.