Shoulder kinetic during pitching in baseball players with scapular dyskinesis.

INTRODUCTION: Shoulder injuries in baseball players cause excessive shoulder load during pitching and scapular dyskinesis (SD). However, the characteristics of pitching kinetics in the shoulder joint with SD are unclear. This study aimed to investigate the effect of SD on pitching kinetics in the shoulder joint of baseball players. METHOD: Seventy-two college and independent league baseball players participated in the study. The pitching motion was measured using an 18-camera motion-capture system. SD was classified into four types (I-IV) using the scapular dyskinesis test (SDT). The pitching kinetics data were analyzed. RESULTS: The agreement of SD in this study was 56/72 (77.8%). SD were classified into 31 abnormal group (type I-Ⅲ) and 25 control group (type Ⅳ). Three participants with measurement failure during the pitching motion analysis were excluded from the analysis. The abnormal group showed a larger maximum value of the glenohumeral normalized anterior joint force than the control group. CONCLUSIONS: These results suggest that an increase in GH anterior force during pitching causes an excessive increase in external rotation of the GH with an insufficient posterior tilt of the scapula with SD. Therefore, baseball pitching with SD may involve shoulder injuries owing to excessive shoulder load during pitching.

Effect of 8-week Shoulder External Rotation Exercise with Low Intensity and Slow Movement on Infraspinatus.

OBJECTIVE: Generally, low-intensity training is recommended as selective training of the infraspinatus muscle. This study aimed to investigate whether an 8-week intervention of low-intensity, slow-movement, external rotation exercise of the shoulder led to an increase in muscle strength with shoulder external rotation and cross-sectional area (CSA) infraspinatus muscle. METHODS: Sixteen healthy male volunteers were randomly assigned to the low-intensity and slow-movement (LS) group (N = 8) or the normal-intensity and normal-speed (NN) group (N = 8). The LS and NN groups performed shoulder external rotation exercises with low intensity and slow movement, and normal intensity and normal speed, respectively. The exercise session consisted of three sets of 10 repetitions, which were performed three times per week for 8 weeks. We measured the CSA of the infraspinatus and muscle strength of the shoulder external rotation before and after the 8-week intervention. RESULTS: A significant increase in infraspinatus CSA from baseline to 8 weeks was found in the LS group (7.3% of baseline) but not in the NN group. No significant differences were found in the muscle strength of shoulder external rotation. CONCLUSION: Our results suggest that low-intensity exercise of the infraspinatus is effective for muscle hypertrophy when performed with slow movement. This finding may help patients who should avoid excessive stress in the early phase of rehabilitation.

Electromyographic Analysis of a Selective Exercise for the Serratus Anterior Muscle Among Patients With Frozen Shoulder and Subacromial Impingement Syndrome.

OBJECTIVE: Patients with shoulder disorders show altered periscapular muscle activity (e.g., decreased serratus anterior and increased upper trapezius activities). We herein devised a novel method for strengthening serratus anterior without excessive upper trapezius activation, named squeezing ball exercise in which patients squeezed a ball between both elbows with maximum voluntary isometric contraction in the horizontal adduction direction with the arms elevated at a 45-degree angle. The present study aimed to investigate whether the squeezing ball exercise could produce high muscle activity in the serratus anterior in patients with frozen shoulder and subacromial impingement syndrome before the rehabilitation intervention. DESIGN: This is a proof-of-concept study. Serratus anterior and upper trapezius activities during squeezing ball exercise were evaluated using electromyography in 16 patients with frozen shoulders and subacromial impingement syndrome. Electromyography signals were normalized using maximal voluntary isometric contraction, and the muscle balance ratios (upper trapezius/serratus anterior) were calculated. RESULTS: The average serratus anterior and upper trapezius activity was 69.9% ± 30.8% and 10.2% ± 6.3% maximal voluntary isometric contraction during the squeezing ball exercise, respectively, whereas the upper trapezius-serratus anterior ratio of the affected side was 0.15 ± 0.07. CONCLUSIONS: The high serratus anterior activation and low upper trapezius-serratus anterior ratio during squeezing ball exercise could be attributed to the limb position where shortened serratus anterior exerts itself without painful subacromial impingement. Squeezing ball exercise could be a novel rehabilitation tool for patients with frozen shoulders and subacromial impingement syndrome.

Scapular dyskinesis type is associated with glenohumeral joint and scapular kinematic alteration during pitching motion in baseball players.

INTRODUCTION: Scapular dyskinesis (SD) is associated with an increased risk of throwing-related shoulder injury onset, resulting in abnormalities in glenohumeral joint (GH) and scapular motions during pitching. The effects of SD on shoulder motion during pitching remain unknown. This study aimed to investigate kinematic alterations in GH and scapular motions during pitching in baseball players with type I SD. METHODS: Sixty-seven university and independent-league baseball players with and without SD were included. Pitching motion was measured using an optical three-dimensional motion capture system, and a SD test was conducted to evaluate SD. SD was classified into types I-IV. The inter-rater reliability of SD assessment was calculated using kappa coefficients. Three-dimensional GH and scapular kinematics during pitching motion were analyzed. RESULTS: The percentage of agreement representing the inter-rater reliability of SD assessment was 77.6% (52/67; kappa coefficient: 0.72). Overall, 24 and 27 participants were categorized into abnormal (type I SD) and normal group (type IV SD), respectively, with normal scapular motion; one individual with type III SD was excluded. The abnormal group exhibited a significantly increased GH external rotation angle (9°) and decreased scapular posterior tilt angle (6°) during the maximum external rotation period compared with the normal group. CONCLUSIONS: Baseball players in the abnormal group showed increased GH motion and decreased scapular motion during pitching. The SD test for the evaluation of type I SD can help predict excessive GH external rotation and decreased scapular posterior tilt during pitching.

A new method of estimating scapular orientation during various shoulder movements: A comparison of three non-invasive methods.

The conventional acromion marker cluster (AMC) method used to estimate scapular orientation cannot adequately represent complex shoulder movements due to soft tissue artifacts. The regression method may have nonlinear error changes depending on humeral elevation angle and elevation plane. Therefore, we aimed to develop a new method of estimating scapular orientation using curved surface interpolation during various shoulder movements, and to compare its accuracy with conventional and regression methods. Thirteen healthy men were recruited. AMC and refractive markers for bony landmarks were placed on the skin. During the preprocess, several shoulder postures, including different arm elevations and elevation planes, were measured using the motion capture system. Premeasured data were used to calibrate the positional relationship between AMC and scapula using curved surface interpolation. Subsequently, scapular orientations were estimated by measuring AMC and body markers of any shoulder posture. To evaluate the accuracy of our methods, 25 elevation postures and six tasks involving postures common to activities of daily living were applied. For tasks requiring greater arm elevation angles, the root mean square error was less in our method than in the conventional and regression methods. Therefore, our method could improve the accuracy of estimating scapular orientation in various elevation postures.

The effect of trunk rotation during shoulder exercises on the activity of the scapular muscle and scapular kinematics.

BACKGROUND: In patients with shoulder disease, kinetic chain exercises including hip or trunk movement are recommended. However, the actual muscle activation and scapular kinematics of these exercises are not known. The purpose of this study was to examine the effect of trunk rotation on shoulder exercises that are devised to improve scapular function. METHODS: Thirteen healthy young men participated in this study. Scaption, external rotation in the first and second positions, and prone scapular retraction at 45°, 90°, and 145° of shoulder abduction were performed with and without trunk rotation. Electromyography was used to assess the scapular muscle activity of the upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA), and electromagnetic motion capture was used to assess scapular motion. The muscle activity ratio, which is the activity of the UT to the MT, LT, and SA, was calculated. These data were compared between 2 conditions (with and without trunk rotation) for each exercise. RESULTS: Adding trunk rotation to scaption, the first external rotation, and the second external rotation significantly increased scapular external rotation and posterior tilt, and all 3 exercises increased LT activation. In addition, trunk rotation with scapular retraction at 90° and 145° of shoulder abduction significantly decreased the UT/LT ratio. CONCLUSIONS: Our findings suggest that shoulder exercises with trunk rotation in this study may be effective in patients who have difficulty in enhancing LT activity and suppressing excessive activation of the UT or in cases in which a decreased scapular external rotation or posterior tilt is observed.

Kinematic characteristics of the scapula and clavicle during military press exercise and shoulder flexion.

BACKGROUND: The military press is an exercise frequently prescribed for scapular and shoulder rehabilitation. Although this exercise has previously been analyzed by electromyography, its kinematic features remain poorly understood. In this study, we aimed to clarify these features of the military press and suggest relevant clinical applications. METHODS: Sixteen healthy men participated in this study. The participants performed the military press while holding 2 kg weights, as well as shoulder flexion with and without 2 kg weights, and an electromagnetic motion capture system was used to analyze the kinematic features of the scapula, clavicle, and humerus during these exercises. The motions of the scapula and clavicle were analyzed at 10° increments of shoulder flexion from 30° to 120°. RESULTS: The military press involved less scapular internal rotation, greater upward rotation, and greater posterior tilt than shoulder flexion with or without weights, especially in the starting to middle range of shoulder flexion. Greater clavicular retraction and elevation were also seen during the military press. DISCUSSION: The movements of the scapula and clavicle during the military press differ significantly from those during shoulder flexion with and without weights. The kinematic features of the military press, which involved less scapular internal rotation, greater upward rotation, and greater posterior tilt than did shoulder flexion, may make it a useful re-education exercise (if pain allows) for patients with decreased scapular external rotation, upward rotation, and posterior tilting. The results of this study might provide a kinematic basis for the use of this widely performed shoulder exercise.