Influence of flexor pronator muscle contraction on medial elbow joint space distance in high school baseball players: a cross-sectional study.

BACKGROUND/HYPOTHESIS: The contraction of the flexor pronator muscles (FPMs) plays an important role in stabilizing the elbow joint in baseball players. However, the influence of different types of contractions on the medial joint space (MJS) in high school baseball players is not well understood. This study aimed to elucidate the effects of individual or combined contractions of the FPMs, specifically the flexor carpi ulnaris, flexor digitorum superficialis (FDS), pronator teres (PT), palmaris longus, and flexor carpi radialis, on the MJS in high school baseball players. We hypothesized that contractions, particularly of the FDS, PT, and flexor carpi radialis, would lead to a narrowing of the MJS.

METHODS

The study included 36 high school baseball players who executed 9 different contraction tasks related to the FPMs (including a resting state) in a randomized order. The MJS was measured using ultrasound equipment and compared with the resting state. The Friedman test, as a repeated-measures one-way analysis of variance, was performed, followed by Steel's test for multiple comparisons. All analyses were conducted using EZR software, with a significance level set at 5%.

RESULTS

The repeated-measures one-way analysis of variance and the Friedman test revealed a significant difference among the 9 contraction tasks (P < .001). Using Steel's test, a significant reduction in the MJS (mean ± standard deviation) was observed compared with the resting state (4.8 ± 1.2 mm), particularly in contraction tasks involving the PT (4.0 ± 1.0 mm, P = .017), FDS and PT (4.0 ± 1.1 mm, P = .007), and flexor carpi ulnaris, FDS, and PT (4.0 ± 1.1 mm, P = .008).

CONCLUSIONS

Incorporating the PT into contraction tasks significantly reduced the MJS, emphasizing the important role of the PT in elbow joint stability. More work is required to see if the results of this study can be used to develop injury prevention and rehabilitation strategies.