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Abstract
Background: Unilateral shoulder bag carrying became one of the most popular way of carrying among different populations. This asymmetric carrying causes many physical, physiological and biomechanical problems. However, there is a relative dearth of research concerning single strap bags that are associated with requisite asymmetric loading. Purpose: investigating the Influence of carrying unilateral shoulder bag on myoelectrical activity of Latissimus Dorsi muscle in normal females. Subjects: Thirty normal female students from Faculty of Physical Therapy, Cairo University. Their ages ranged between 18 and 22 years. Method: Root Mean Square(RMS) of myoelectrical activity of Latissimus Dorsi muscle was measured under three conditions 1-Maximum voluntary contraction of latissimus Dorsi muscle for 5 seconds. 2-Carrying unilateral shoulder bag with 10% of body weight on non dominant shoulder for 5 minutes. 3- Carrying unilateral shoulder bag with 15% of body weight on non dominant shoulder for 5 minutes, with ten minutes rest in between. Results: During carrying 10% of BW, the RMS of EMG of non dominant side was less than of the dominant side with mean (6.20 and 10.14 mv) respectively which was highly significant(P=0.001). During carrying 15% of BW, the RMS of EMG of non dominant side was less than of the dominant side with mean (6.95 and 9.08 mv) respectively which was highly significant(P=0.001).When comparing carrying 10% and 15% of BW, there was a significant increase in the RMS of EMG of non dominant Latissimus Dorsi muscle during carrying unilateral shoulder bag containing 15% of body weight than carrying 10% of body weight with mean (6.95 and 6.20 mv) respectively and (P=0.008); But, there was no significant difference in RMS of EMG activities of dominant Latissimus Dorsi muscle between carrying unilateral shoulder bag containing 10% and 15% of body weight with mean (10.14 and 9.08 mv) respectively with (P = 0.209) Conclusion: Increasing the weight carried in the unilateral shoulder bag lead to asymmetrical increase in back muscles activity which may lead to pathological and biomechanical changes.