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Background: Little is known about the optimal exercise intensity and the effects of arm position on elastic resistance exercise. The purpose of this study was to investigate scapular muscle activity in different arm positions utilized during standing elastic resistance exercise. Hypothesis: Lower trapezius (LT), serratus anterior (SA), and infraspinatus (IS) muscle activity will vary across arm positions above shoulder level. Also, oscillation resistance exercise will result in increased muscle activity compared with isometric contraction. Study Design: Controlled laboratory study. Level of Evidence: Level 4. Methods: A total of 19 uninjured male collegiate baseball players volunteered to participate in this study. The electromyography (EMG) activity of the LT, upper trapezius (UT), middle deltoid (MD), SA, and IS muscles was determined using surface EMG in 3 arm positions: diagonal pattern 1 (D1), 120° of shoulder abduction (120), and 90° shoulder abduction with external rotation and elbow flexion (90/90) during both isometric contraction and oscillation resistance exercise. Results: No difference in EMG activity of the LT muscle was found between the 120 and 90/90 position. However, the 120 position increased UT and MD muscle activity significantly more than those of the 90/90 position. The D1 arm position significantly increased SA muscle activity more than the 120 and 90/90 positions while the LT muscle activity was nearly silent. Conclusion: The standing 90/90 position effectively generated both LT and IS muscle EMG activity while minimizing both UT and MD muscle activity. Clinical Relevance: The use of oscillation movements under elastic loading can create high muscle activation in the LT muscle without an adverse effect of the humeral head position and scapular rotation.

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Background Baseball players are aware of the potential of shoulder problems due to repetitive throwing. However, few studies have examined how pitching repeatedly affects the thoracic spine and shoulder. Purpose This study aimed to determine the effects of pitching repeatedly on the endurance of trunk muscles and kinematics of the thoracic spine and shoulder. Study design Cohort study Methods Trunk muscle endurance was assessed in flexion, extension, and lateral flexion positions in 12 healthy amateur baseball players. The positions of stride foot contact (SFC) during the early cocking phase and maximal shoulder external rotation (MER) during the late cocking phase were used to compute the thoracic and shoulder kinematics in degrees. Participants were then asked to throw 135 fastballs (~9 innings with 15 throws per inning). Throwing motions were monitored throughout the first, seventh, eighth, and nine innings, whereas trunk muscular endurance was assessed before and after the repetitive throwing activity. Ball speed during pitching was measured using a radar gun. All outcome measures were statistically compared to examine differences over time. Results The trunk muscle endurance declined after the throwing task. In the eighth inning, compared with the first inning, the thoracic rotation angle at the SFC increased toward the throwing side. In contrast, the shoulder horizontal adduction angle at MER decreased in the seventh and ninth innings. Conclusion With repeated pitching, trunk muscle endurance gradually declines, and repetitive throwing significantly altered kinematics of the thoracic rotation at SFC and shoulder horizontal plane at MER. Level of Evidence 2a

The aim of this study is to investigate the characteristics of pre-existing physical factors associated with the onset of Osgood-Schlatter disease (OSD) in junior soccer players. Fiftynine junior soccer players of the elementary school were included in this study. The boys who had been diagnosed as OSD were excluded. At the time of the first investigation, the subjects were examined through physical evaluation and an ultrasonography. The subjects were followed up one and a half years, and the tibial tuberosity was classified according to the growth stages using the ultrasonography. After the end of follow-up period, the subjects were divided into two groups, those with signs and symptoms of OSD that appeared during the follow up period and those without that. The Mann-Whitney U test was used for the comparison between OSD group's and control group's initial assessments. The players who were followed up for one and half years were 38 people. 5 knees of the 4 players were clinically diagnosed as OSD (OSD group), and the remaining 34 players with no symptoms of the OSD constituted the control group. The range of the bilateral hip external rotation, straight leg raise of the non-dominant side, and knee flexion in the OSD group were significantly lower than those in the control group (p < 0.05). We concluded that a decrease in specific joint flexibility might be related with the onset of OSD.