[ effect of muscle fatigue on normal biomechanics of shoulder girdle: a systematic review of the literature]

Objective: Dynamic stability in shoulder is an important element in life and any disorder in muscular function which helps maintain this stability leads to shoulder pathology. One of these disturbing factors is fatigue. According to the research team information until now there has not been a study investigated systematically the effect of fatigue on shoulder girdle biomechanics. So the purpose of this systematic review is to determine the effect of muscle fatigue on normal shoulder girdle biomechanics

Materials and Methods: This study is a systematic review based on search in PubMed, Scopus, Elsevier, Ovid, CINAHL, Science Direct, ProQuest, Thompson, EMBASE and Medline databases for the period of 1995- 2012. The keywords used were Shoulder, Muscle Fatigue, Proprioception and Kinematics. Two levels of reevaluation were used on 350 citations

Results: The search strategy resulted in 350 results out of which 22 papers met the criteria for this study. Variation among studies in terms of sample size, fatigue protocol and method of measurement were investigated

Conclusion: Evidences demonstrated muscle fatigue leads to change in activation pattern of muscles shoulder girdle and consequently kinematics as well as reduction in proprioception during different positions and movements in both scapulothoracic and glenohumeral joints. Generally the results indicated that there are sufficient evidences based on the effect of fatigue on the muscular fatigue has disturbance effects on shoulder girdle kinematics and could alter the normal biomechanics

[Reproducibility of maximum voluntary isometric contraction in "empty can" position during surface electromyographic analysis of shoulder muscles]

Due to the frequent use of surface electromyography as a tool for the study of muscle function, to accurately compare electromyographic data from different muscles and different subjects, it is necessary to normalize the integrated data obtained from each muscle. The most common normalization technique is the use of maximum voluntary isometric contraction [MVIC] of a predetermined isometric movement as the reference electromyographic signal. The purpose of this study was to determine the Reproducibility of maximum voluntary isometric contraction of shoulder muscles in Empty Can position test and the correlation between force and MVIC of shoulder muscles. The electromyographic activity of these four muscles [anterior and middle deltoid, upper and lower trapezius] was examined in 20 healthy subjects [10 men and 10 women with 31.25 +/- 8.92 age]. Muscle force was determined by dynamometer. Each test repeated 3 times. Results showed that same day test retest reliability coefficients were significant [ICC>95%], but separate day test retest reliability coefficients were not significant. Maximum muscle force did not relate to any of muscles MVIC amplitude. Reproducibility results may be due to electrode placement, emotional and physical condition of subjects and the large range of motion of shoulder and compensatory movements of shoulder and trunk