A study of the isokinetic strength ratio of shoulder internal and external rotators in badminton players

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A study of the isokinetic strength ratio of shoulder internal and external rotators in badminton players

 

Author: Lam, Chuk-wai
Title: A study of the isokinetic strength ratio of shoulder internal and external rotators in badminton players
Degree: M.Sc.
Year: 2000
Subject: Shoulder joint
Shoulder joint -- Rotator cuff
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Rehabilitation Sciences
Pages: iii, 80 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1541803
URI: http://theses.lib.polyu.edu.hk/handle/200/3803
Abstract: The static and dynamic stability of glenohumeral joint is based on the capsuloligamentous structures and musculotendinous units respectively. Any muscle imbalance may induce instability and renders the shoulder susceptible to injury. In the overhead sporting movement, two critical instances (late cocking and deceleration phases) have been identified as potential causes of shoulder injury. The co-work phenomenon (eccentric antagonist and concentric agonist) of the internal and external rotators in the late cocking and deceleration phases has well been investigated. However, studies in the past have only focused on the concentric against concentric or eccentric against eccentric internal and external rotator strength ratios. Only two studies were found in the literature, which reported the co-work relationship of the shoulder rotators. However, their results were inconclusive and there were limitations in both studies. This study examined the Mode Specific Work Ratio (MSWR) of the eccentric antagonist against concentric agonist in the two critical phases of the overhead sporting movement (late cocking and deceleration), and compared the ratio between the dominant and non-dominant shoulders. It was hoped that the ratios found would be more appropriate for analyzing muscle imbalance of the shoulder rotators, so as to develop a better strategy for training, injury prevention and rehabilitation. Twenty-five male badminton players aged between 21 to 40 were tested. The tests were conducted with a Cybex 6000 isokinetic machine at a testing speed of 120o/second. The testing position of the subject was in crook lying with the shoulder at 90o of abduction. The MSWR found for the late cocking phase were 1.9 for the dominant shoulder and 1.3 for the non-dominant shoulder (p=0.000). In the deceleration phase, the MSWR were 1.1 for the dominant shoulder and 1.3 for the non-dominant shoulder (p=0.002). There was a statistical significant difference of the MSWR between the dominant and non-dominant shoulder in both the late cocking and deceleration phases. This indicated a different strength profile in shoulder rotators amongst the badminton players. The significantly higher MSWR in the late cocking phase of the dominant shoulder indicated that a higher eccentric internal rotation force was necessary. This could be due to the demand of abrupt stopping at the desirable position at the end range of external rotation within a very short moment, and reservation of energy for acceleration. The low MSWR found in the deceleration phase could be because of the skill compensation in badminton to relieve the concentric internal rotation force and no need for extra energy of the eccentric external rotators. The lower MSWR found in the dominant side might be due to the skill compensation and underlying shoulder pathology / structural adaptation.

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