Effects of repetitive baseball throwing on hip muscle strength and trunk and pelvic motions at the shoulder's maximum external rotation position during the late cocking phase and ball release.

[Purpose] This study aimed to investigate the changes in the trunk and pelvic lateral tilt angles at the shoulder's maximum external rotation during the late cocking phase (MER) and ball release (BR) and hip muscle strength during repetitive throwing. [Participants and Methods] In this study, 12 male baseball players participated. During the throwing, which was filmed using a high-speed video camera, the trunk and pelvic lateral tilt angles toward the nonthrowing side were measured at the MER and BR. Hip muscle strength during abduction, adduction, and external internal rotations were measured on the throwing and nonthrowing sides. Repetitive throwing was performed for nine innings, with 15 pitches per inning. Throwing motion was compared during innings 1, 7, 8, and 9. Hip muscle strength was measured before and after repetitive throwing. [Results] Compared with the trunk lateral tilt angle toward the nonthrowing side at BR in inning 1, the angle in innings 8 and 9 increased. The strength of hip abduction, adduction, and external and internal rotations on the throwing and nonthrowing sides decreased after repetitive throwing. [Conclusion] Hip muscle strength decreases after 135 pitches, and throwing >120 pitches changes the trunk lateral tilt angle at BR.

Effects of Repetitive Pitching on Trunk Muscle Endurance and Thoracic and Shoulder Kinematics.

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 task dependent differences in electromyography activity of hamstring muscles during leg curls and hip extensions.

This study aimed to investigate the influence of the task type on the relative electromyography (EMG) activity of biceps femoris long head (BFlh) to semitendinosus (ST) muscles, and of proximal to distal regions during isometric leg-curl (LC) and hip-extension (HE). Twenty male volunteers performed isometric LC with the knee flexed to 30° (LC30) and 90° (LC90), as well as isometric HE with the knee extended (HE0) and flexed to 90° (HE90), at 40% and 100% maximal voluntary contraction (MVIC). Hip position was neutral in all conditions. EMG activity was recorded from the proximal and distal region of the BFlh and ST muscles. BFlh/ST was calculated from the raw root-mean-square (RMS) amplitudes. The RMS of 40% MVIC was normalized using MVIC data and the proximal/distal (P/D) ratio of normalized EMG (NEMG) was calculated. The BFlh/ST ratio was higher in HE0 than in LC90 during MVIC and 40% MVIC (p<0.05), and was higher in HE90 than in LC90 (p<0.05) during 40% MVIC at the proximal region, whereas no difference was observed between HE0 and LC30. There was no inter-task difference in BFlh/ST ratio in the distal region. Furthermore, the P/D ratio was higher in LC90 than in LC30 and HE0 (p<0.05) in BFlh and ST muscles, and was higher in HE90 than in LC30 and HE0 (p<0.05) in BFlh during 40% MVIC. However, there was no difference in P/D ratio between LC30 and LC90, and HE0 and HE90. This showed that there was no task-dependent difference in the EMG activity of the BFlh muscle relative to the ST muscle between prone hip extension and prone knee flexion when the knee joint was set at an equivalent angle. Similarly, there was no task-dependent difference in the NEMG of the proximal region relative to the distal region in BFlh and ST muscles during 40% MVIC.

Analysis of Scapular Muscle EMG Activity During Elastic Resistance Oscillation Exercises From the Perspective of Different Arm Positions.

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.