Evaluation of the effect of external load activation of periarthicular shoulder muscles

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. 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. 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). 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.