Repetitive pitching decreases the elbow valgus stability provided by the flexor-pronator mass: the effects of repetitive pitching on elbow valgus stability

Baseball pitching induces a large elbow valgus load, stressing the ulnar collateral ligament (UCL). Flexor-pronator mass (FPM) contraction contributes to valgus stability; however, repetitive baseball pitching may weaken the FPM contractile function. The present study investigated the effects of repetitive baseball pitching on the medial valgus stability measured using ultrasonography. We hypothesized that repetitive pitching would decrease elbow valgus stability. This was a controlled laboratory study. Fifteen young male baseball players at the collegiate level (age: 23.0 ± 1.4 years) were enrolled. The medial elbow joint space was measured using ultrasonography (B-mode, 12-MHz linear array transducer) in the following three conditions: at rest (unloaded), under 3 kg valgus load (loaded), and under valgus load with maximal grip contraction to activate FPM (loaded-contracted). All measurements were performed before and after the pitching tasks, which comprised five sets of 20 pitches. Two-way repeated-measures analysis of variance was applied to determine changes in the medial elbow joint space. The post hoc test with Bonferroni adjustment was applied to assess the changes within the time and condition. The medial elbow joint space was significantly greater under the loaded than the unloaded and loaded-contracted conditions both before and after pitching (P