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ABSTRACT Background and Aims: In new prospect of motor control, the effect of muscle force is considered important not only in producing movement but also in inducing stability and control of activity. The aim of present study was to evaluate the electrical activity of periarthicular shoulder muscles by surface EMG in order to identify the muscular activity during series of static and dynamic pattern of movements. Materials and Methods: This Quasi experimental study was performed on 30 healthy male and female volunteers with age of 20-30 years and mean age of 23.2±2.9. The subjects were enrolled into this study by simple non-probability sampling and were exposed to different movement patterns randomly. During the experiment the surface EMG of every muscle was recorded. The external load applied to shoulder was assessed at three levels in static as well as dynamic situations. Results: According to the results of this study, increasing the external load on the scapulothoracic muscles caused a significant increase in the activity of the muscles except for upper trapezious muscle in descending phase of the movement (p<0.05). After increasing the external load on shoulder in ascending phase, most of the investigated muscles showed significant differences in their activities. (p<0.05). In static situation by application of external load only teres major muscle showed significant difference in its activity compared to the reference position (p=0.01). Conclusion: It can be concluded that application of external load during ascending phase of push up is more effective than its application during descending phase. It can be claimed that during ascending phase slight increase in external load as low as 2% of body weight, would induce more alterations in muscular activity compared to higher external load such as 4% of body weight, but in static situation no significant change could be detected. Key words: Electromyography, Muscle activity, Shoulder stability. Conflict of Interest: Nill Received: Aug 16, 2010 Accepted: Nov 18, 2010

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ABSTRACT Background and Aim: The aim of this study was to determine the effect of one-session of whole body vibration training on isokinetic strength of rotator cuff and shoulder proprioception Materials and Methods: 32 students experienced three positions including control (no vibration), push up with straight elbow and push up with semi flexed elbow (two vibration positions) for 2 minutes with 30 minutes interval between positions. After control position, vibration positions were tested on a random basis by means of a power plate device (Freq: 30Hz and Amp: low ). The isokinetic strength of rotator cuff and shoulder proprioception were measured in angle repositioning test in 3 target angles of 0°, 45° and 90° by means of Kin-Com dynamometer before and after each position. Then the results of 3 positions were compared with one another. Results: Despite decreased dynamic strength of medial rotators after 3 positions, this decrease was significantly less in push up with straight elbow than that in control position (p=0.03). Also there was a significant difference in concentric MPT of lateral rotators between 3 positions so that, control position caused the greatest decline in lateral rotators strength (p=0.01) and push up with straight elbow was more effective than push up with semi flexed elbow (p=0.03). Moreover, There was a significant improvement in angle repositioning in 3 positions but only in zero degree a significant difference was detected between the push up with semi flexed elbow position and the control position (p=0.03). No significant change in muscle strength was found between push up with straight elbow and semi flexed elbow positions. Conclusions: The results of this experiment show that a two minute single-session of whole body vibration is relatively a good stimulation for neuromuscular system in young and healthy individuals. Key words: Whole body vibration training, Rotator cuff muscle strength, Proprioception Conflict of Interest: Nill Received: Aug 16, 2010 Accepted: Nov 15, 2010