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

Abstract

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

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

“…Regarding the factor that causes changes in trunk lateral tilt during the acceleration phase, including at BR, the trunk lateral flexion strength on the throwing and nonthrowing sides decreased with repetitive throwing 15 ) . Excessive contralateral trunk tilt during pitching is associated with the imbalance between oblique muscles on the dominant and nondominant sides 30 ) .…”

“…In addition, to reduce the load on the shoulder and elbow during pitching, the trunk and pelvis lateral tilt motions should be controlled 8 , 10 , 11 , 12 ) . However, only a few studies have examined changes in the trunk and pelvic lateral tilt motions associated with repetitive throwing among nonstrenuous training-level baseball players 15 ) . In addition, only a few studies have examined the hip muscle strength that controls the pelvic coronal plane motion before and after repetitive throwing 19 ) .…”

“…Participants were allowed to warm-up and stretch for 5 minutes before the repetitive throwing task. The participants threw 135 fastballs (9 innings of 15 per inning at ball intervals of 15 s) with their maximum effort from the set position toward the target 15 ) . The distance between the participants and the target was 3 m, and the size of the target was 1.1 × 1.1 m. The official baseball (ZETT Corp., Osaka, Japan), weighing 145.0–147.0 g, was used during the repetitive throwing task.…”

“…The hip muscle strength was measured before and after the repetitive throwing task. The throwing motion was measured on the 1st, 2nd, and 3rd pitches of the 1st inning; 103rd, 104th, and 105th pitches of the 7th inning; 118th,119th, and 120th pitches of the 8th inning; and 133rd, 134th, and 135th pitches of the 9th inning 15 ) . In a typical Japanese baseball game, more than 100 pitches are often thrown.…”

“…Based on these reports, trunk lateral tilt motion during pitching is believed to be unaffected by the repetitive throwing task; however, drawing a conclusion is difficult because all athletes in the studies by Escamilla et al 13 ) and Pei-His et al 14 ) were at a high competition level. Conversely, only a few studies have examined changes in the trunk lateral tilt motion during pitching among athletes who are not at a strenuous training level 15 ) , necessitating further investigation. Moreover, shoulder internal rotation and elbow varus moments, which are related to throwing injuries, are maximal just before MER and occur at high values over BR 16 , 17 ) .…”