Kotoshiba S1, Urabe Y1, Maeda N1, Sasadai J1, Hara M2
1Hiroshima University, Graduate School of Biomedical and Health Sciences, Department of Sports Rehabilitation, Hiroshima, Japan, 2Hisatsune Hospital, Orthopaedic Surgery, Fukuoka, Japan
Background: The infraspinatus muscle activity in pitching motion is important to the stability of the glenohumeral joint during follow through phase (Kibler et al, 2007). We reported that baseball players with shoulder injury had the high activity of infraspinatus during acceleration phase (Kotoshiba et al, 2017). As an evaluation of throwing injury, Hara (2007)classified baseball players with throwing injury into four type (A, B, C, S) using X-ray with the zero positioned. Type S was recognized slipping phenomenon which posterior or lateral sliding of the humeral head at the zero positioned, and the instability in the glenohumeral joint was involved with that (Hara, 1999). However, the influence of the slipping phenomenon on the infraspinatus activity during pitching motion has not been investigated.
Purpose: The aim of this study was to investigate infraspinatus activity during throwing motion of baseball players who were admitted the instability at elevation position.
Methods: Twenty baseball players with shoulder injury participated in this study. Participants were separated into two groups: Type S group (n=10) and Type A group (n=10). Type S was defined as the center of the humeral head was positioned on the outside of the lateral edge of the glenoid in the zero positioned using X-ray image. Type A was defined as the long axis of the humerus matched the spine of scapula (Hara, 2004). The pitching motions were recorded by two high-speed cameras(Sports Coaching Cam, Sports Sensing, Japan), and shoulder external rotator muscle activity was measured using electromyography (TelemyoG2, Noraxon, Japan). EMG sensors were placed on the infraspinatus and deltoid posterior as shoulder external rotators. According to the video analysis, the pitching motion was divided into four event segments as follows: early cocking, late cocking, acceleration, and follow through phases (Jobe et al, 1983). Statistical analysis was performed using EZR ver. 1.32. software. Mann-Whitney U test was used to determine the difference in the muscle activity in Type A vs Type S group at four phases respectively. The significance level was set at 0.05.
Results: In the acceleration phase, the infraspinatus activity revealed a significantly greater value in the Type S group (56.6±31.2%MVC) than that of the Type A group (33.0±16.1%MVC) (p 0.05). There was no significant difference in other phases between both groups. There was no significant difference in deltoid posterior activity between both groups.
Conclusion(s): Type S has instability in the glenohumeral joint at the elevation position. This study suggested that the instability such as a slipping phenomenon has increased the infraspinatus muscle activity during the acceleration phase. Therefore, it was considered the high activity of infraspinatus need for stability. By repetitive pitching with hyper activity of infraspinatus on the slipping shoulder may cause fatigue and dysfunction.
Implications: This survey showed the influence of the instability in the glenohumeral joint on the infraspinatus activity during pitching motion in baseball players with shoulder injury. It would lead to preventing and treatment shoulder injury.
Keywords: Infraspinatus, Pitching motion, Instability in glenohumeral joint
Funding acknowledgements: We have no funding acknowledgment in this study.
Purpose: The aim of this study was to investigate infraspinatus activity during throwing motion of baseball players who were admitted the instability at elevation position.
Methods: Twenty baseball players with shoulder injury participated in this study. Participants were separated into two groups: Type S group (n=10) and Type A group (n=10). Type S was defined as the center of the humeral head was positioned on the outside of the lateral edge of the glenoid in the zero positioned using X-ray image. Type A was defined as the long axis of the humerus matched the spine of scapula (Hara, 2004). The pitching motions were recorded by two high-speed cameras(Sports Coaching Cam, Sports Sensing, Japan), and shoulder external rotator muscle activity was measured using electromyography (TelemyoG2, Noraxon, Japan). EMG sensors were placed on the infraspinatus and deltoid posterior as shoulder external rotators. According to the video analysis, the pitching motion was divided into four event segments as follows: early cocking, late cocking, acceleration, and follow through phases (Jobe et al, 1983). Statistical analysis was performed using EZR ver. 1.32. software. Mann-Whitney U test was used to determine the difference in the muscle activity in Type A vs Type S group at four phases respectively. The significance level was set at 0.05.
Results: In the acceleration phase, the infraspinatus activity revealed a significantly greater value in the Type S group (56.6±31.2%MVC) than that of the Type A group (33.0±16.1%MVC) (p 0.05). There was no significant difference in other phases between both groups. There was no significant difference in deltoid posterior activity between both groups.
Conclusion(s): Type S has instability in the glenohumeral joint at the elevation position. This study suggested that the instability such as a slipping phenomenon has increased the infraspinatus muscle activity during the acceleration phase. Therefore, it was considered the high activity of infraspinatus need for stability. By repetitive pitching with hyper activity of infraspinatus on the slipping shoulder may cause fatigue and dysfunction.
Implications: This survey showed the influence of the instability in the glenohumeral joint on the infraspinatus activity during pitching motion in baseball players with shoulder injury. It would lead to preventing and treatment shoulder injury.
Keywords: Infraspinatus, Pitching motion, Instability in glenohumeral joint
Funding acknowledgements: We have no funding acknowledgment in this study.
Topic: Sport & sports injuries; Musculoskeletal: upper limb; Disability & rehabilitation
Ethics approval required: Yes
Institution: Hisatsune Hospital
Ethics committee: Ethics Committee
Ethics number: 4
All authors, affiliations and abstracts have been published as submitted.
