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M. Yoshimi1, Y. Urabe1, K. Fukui1, S. Kotoshiba1, N. Maeda1
1Hiroshima Univercity, Graduate School of Biomedical and Health Sciences, Hiroshima, Japan
Background: Throwing injuries of the shoulder joint often occur from late coking phase to acceleration phase during pitching motion, maximum shoulder external rotation (MER). Shoulder external rotation consists of a combined movement of the glenohumeral (GH) joint, scapulothoracic (ST) joint, thoracic spine, and thorax. A previous study reported that the coordination of the ST, GH, and trunk movements plays an important role in the prevention of throwing injuries (Miyashita et al., 2010). Both a decrease in ST movement and an increase in GH movement are risk factors for throwing injuries; however, it is unclear whether thoracic motion restriction affects these movements. In addition, during the pitching motion, MER is not generated by the concentric contraction of the external rotators, but rather by the eccentric contraction of the internal rotators (Miyanishi et al., 1997). To prevent throwing injuries, it is necessary to examine the changes in ST and GH movements during eccentric shoulder external rotation.
Purpose: The aim of this study was to investigate differences in ST-joint and GH-joint movements during eccentric shoulder external rotation with and without thoracic motion restriction.
Methods: Eight healthy right-handed men (age: 22.5 ± 1.6 y.o.; height: 172.4 ± 4.1 cm; weight: 62.2 ± 4.9 kg) participated in this study. Each performed shoulder external rotation of the dominant arm at 90° of shoulder abduction while holding a 0.5 kg dumbbell, that started at 75° of shoulder external rotation. A 38-mm cotton bandage tape and a 50-mm elastic bandage tape (Nitoms) were attached to the 5th and 10th rib positions, respectively, to restrict thoracic motion. Shoulder external rotation, ST posterior tilt, and GH external rotation angle were measured using an electromagnetic tracking device (Liberty, Polhemus). The MER angle and angular changes in both the ST posterior tilt and GH external rotation from the starting position to the MER, with and without thoracic motion restriction, were compared using the paired t-test. The significance level was set at 5%.
Results: Significant reduction in the ST posterior tilt (with restriction: 6.6 ± 4.4°; without restriction: 10.0 ± 3.5°, p<0.05) and an increased GH external rotation (with restriction: 26.9 ± 14.3°; without restriction: 17.1 ± 9.0°, p<0.05) were observed with thoracic motion restriction than without it. However, no significant difference was observed in the MER angle (with restriction: 114.4 ± 9.7°, without restriction: 115.9 ± 9.9°, p = 0.70).
Conclusion(s): Although no significant change was observed in the MER angle, it was found that the movement of the shoulder complex was affected by thoracic motion restriction. Insufficient ST movements and excessive GH movements increase mechanical stress on the shoulders (Seitz et al., 2012); therefore, thoracic motion restriction might alter ST and GH movements, thereby causing throwing injuries.
Implications: Thoracic motion restriction may cause changes in ST and GH movement during static eccentric shoulder external rotation. Similar future investigations are necessary for dynamic movements such as real pitching motion.
Funding, acknowledgements: We have no funding acknowledgement in this study.
Keywords: Thoracic motion restriction, Shoulder motion, Three-dimensional motion analysis
Topic: Sport & sports injuries
Did this work require ethics approval? Yes
Institution: Hiroshima University
Committee: Ethical Committee for Epidemiology
Ethics number: E-1365
All authors, affiliations and abstracts have been published as submitted.
