The shoulder girdle is the most mobile joint in the body. The stability of the joint is lowered to achieve greater mobility. Due to this, the normal function of the shoulder girdle requires retained function of dynamic joint stabilizers and synchronised operation of the shoulder joint with the neighbouring joints. In throwing sports, the movements, which are mostly executed above the head, represent a high risk for damaging the shoulder girdle as the shoulder is exposed to great strain and forces during throwing, serving and hitting.
The measured strength of the rotator cuff in overhead athletes showed bilateral differences of strength, namely lower strength of external rotators and greater strength of internal rotators in comparison to the non-throwing arm. The strength ratio between the internal and external rotation is therefore lower in the throwing/playing arm. That is why regular monitoring of risk factors, such as the strength ratio of the rotator cuff, in healthy and injured athletes is extremely important for their health.
In this master’s thesis we focused on comparing the ratio of internal and external shoulder rotation and the ratio between the dominant and non-dominant arm. With this we wanted to determine whether and how these parameters are related to shoulder injuries.
Our research included 73 young tennis players. The average age of the participants was 17 years. Of the 73 participants, 36 (49%) reported shoulder injuries. We used the manual dynamometer MicroFET 2 Wireless to measure isometric strength of the external and internal shoulder rotators.
With this research we rejected both hypotheses. The results showed no relation between intermuscular ratio and shoulder pain. We also did not find a connection between strength asymmetry and shoulder injuries.
Based on the results of this research, we can infer that testing the muscle strength of external and internal shoulder rotators is insufficient to determine potential injuries or the cause of shoulder injuries and pain, as these data do not provide enough information. We propose that in the case of injuries to the shoulder girdle, we must look at a much broader picture due to the joint’s complex structure and consider other potential factors which could cause injuries or pain.
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