Relationship between Isometric Muscle Force and Surface EMG of Wrist Muscles at Different Shoulder and Elbow Angles

Purpose: The purpose of this study is to investigate the relationship between myoelectric activities of wrist flexors and extensors and hand grip strength at four different positions of shoulder and elbow joints. Subjects: Thirteen normal male university students volunteered to participate in this study. Their mean ages, weights and heights were 19.6 (± 1.06) years, 75.9 (± 7.51) Kg and 173.5 (± 4.67) cm respectively. Method: Four positions of shoulder (Sh) and elbow (El) joints were assumed during which both hand grip strength and EMG of wrist flexors and extensors were measured and correlated. The tested positions were (1) 0° Sh 90° El, (2) 90° Sh flexion 90° El flexion, (3) 90° Sh abduction 0° El, and (4) 90° Sh abduction 90° El flexion. Each subject was instructed to produce a powerful grip and maintain this grip force for 5 seconds during which the raw EMG signals were recorded. Three trials of recording of EMG and grip strength were collected with a rest period of 3 minutes between each trial to prevent fatigue Analysis: Pearson Product Moment Correlation Coefficient was conducted using StatGraphics plus with alpha level of significance set at 0.05. Results: Correlation between hand grip strength measured in kg and Root Mean Square (RMS) EMG of wrist flexors revealed significant positive correlation between both variables in positions (2), (3) and (4) (r = 0.38, 0.45, 0.48 respectively). Correlation between hand grip strength and RMS EMG of wrist extensors revealed significant positive correlation between both variables only in positions (2) and (3) (r = 0.48, 0.62 respectively). In positions (1) and (4) the (r) values were (r = 0.27, 0.30 respectively) which indicate non significant positive correlation. Conclusion: The findings of this indicated that abducted shoulder with extended elbow is the best position to produce hand grip strength with great correlation between hand grip strength and EMG activities of wrist flexors and extensors. [Ahmed A. Ashour. Relationship between Isometric Muscle Force and Surface EMG of Wrist Muscles at Different Shoulder and Elbow Angles. J Am Sci 2014;10(5):26-34]. (ISSN: 1545-1003). http://www.jofamericanscience.org. 4