Background: The external rotation (ER) exercise in performed at a 90° abduction of the shoulder joint is an effective to strengthen the infraspinatus. However, failure of the humeral head to control axial rotation during exercise can be increased the posterior deltoid over activity. Biofeedback training is an effective method of promoting motor learning and control it could look forward to activate the infraspinatus selectively by controlling the humeral head during exercise. Objects: The aim of this study was investigated that whether biofeedback for axial rotation was effective to activate selectively the infraspinatus during ER exercise. Methods: The 15 healthy males participated, and all subjects performed both ER exercise in a sitting position with shoulder abducted 90° under conditions with and without axial rotation biofeedback. Exercise was performed in a range of 90° ER, divided into three phases: concentric, isometric, and eccentric. The infraspinatus and posterior deltoid muscle activity were observed using surface electromyography. Results: Both infraspinatus activity (p < 0.01) and infraspinatus to posterior deltoid activity ratio (p = 0.01) were significantly higher with biofeedback however, posterior deltoid activity was significantly lower with biofeedback (p = 0.01). The infraspinatus muscle activity and muscle activity ratio were the highest in the isometric contraction type, and there were significant differences for all contraction types (p < 0.05). Whereas, the posterior deltoid activity was the lowest in the isometric contraction type, and showed a significant difference between isometric and other two contraction types (p < 0.05), but no significant different between concentric and eccentric contraction. Conclusion: Our results indicate that the axial rotation biofeedback during sitting ER exercise might be effective method to activating selective infraspinatus muscle and recommended to enhance the dynamic stability of the shoulder joint.

Background: Short foot exercise (SFex) is often prescribed and performed in the sport and rehabilitation fields to strengthen intrinsic foot muscles. However, SFex is difficult to perform because of lack of feedback methods. Objects: The aim of this study was to compare the effects of SFex with and without electromyography (EMG) biofeedback on the medial longitudinal arch (MLA) of healthy individuals who maintained a static standing position. Methods: All participants (14 males and 12 females) were randomly divided into two groups (biofeedback and non-biofeedback groups). The EMG activity of the abductor hallucis (AbdH) and tibialis anterior (TA) and the MLA angle on the dominant leg side were measured with the participant in the standing position in the pre- and post-intervention conditions. The intervention session consisted of 15 minutes of SFex with (biofeedback group) or without (non-biofeedback group) EMG biofeedback. The groups were compared using two-way repeated measures analysis of variance. Results: The post-intervention activities of the AbdH muscle (p<.05) and the AbdH/TA ratio (p<.05) were significantly greater in the biofeedback group than in the non-biofeedback group. The activity of the TA (p<.05) and the MLA angle (p<.05) in the biofeedback group were significantly lower in the post-intervention condition than in the pre-intervention condition. Conclusion: The present findings demonstrate that the combination of SFex and EMG biofeedback can effectively facilitate the muscle activity of the AbdH and strengthen the medial longitudinal arch.

Push-up plus has been advocated for increasing the activity of the serratus anterior muscle, the most critical scapular stabilizer. However, no previous study has reported the possibility of compensatory motion on the part of the pectoralis major, which could substitute for the action of the serratus anterior during push-up plus. The aim of the current study was to investigate the immediate effect of electromyography (EMG) biofeedback of the pectoralis major muscle on the pectoralis major, upper trapezius, and serratus anterior muscles during push-up plus. Fourteen healthy young subjects voluntarily participated in this study; each subject performed push-up plus from the quadruped position, in two conditions (i.e., with or without visual and auditory biofeedback). Surface EMG was used to measure pectoralis major, serratus anterior, and upper trapezius activity. A paired t-test was used to determine any statistically significant difference between the two conditions. Additionally, effect size was calculated to quantify the magnitude of EMG biofeedback in each muscle. Visual and auditory feedback reduced pectoralis major muscle activity significantly (p=.000) and increased the serratus anterior muscle activity significantly (p=.002), but did not induce a significant difference in upper trapezius muscle activity (p=.881). Thus, it is concluded that the visual and auditory feedback of pectoralis major muscle activity can be used to facilitate serratus anterior muscle activity during push-up plus.