The effect of baseball grips on the hardness of the flexor digitorum superficialis.

Background: In baseball pitches, the forkball requires a special grip, pinching the ball between the second and third fingers to achieve the resulting breaking ball trajectory. We hypothesized that the forkball grip would have a substantial impact on the hardness of the flexor digitorum superficialis. The aim was to quantify and clarify the change in the hardness of the flexor digitorum superficialis due to the forkball grip.

Methods: Twenty-one adult male subjects were recruited and instructed to perform two baseball grips with the ball: fast and forkball, and the rest without the ball. The shear wave speeds of the pronator teres, flexor carpi radialis, flexor digitorum superficialis, and flexor carpi ulnaris were measured using shear wave elastography.

Results: In the forkball grip, compared with the fastball grip and the rest without the ball, the shear wave speed of the flexor digitorum superficialis was significantly higher than those of the pronator teres, flexor carpi radialis, and flexor carpi ulnaris (P<0.001), indicating that muscle hardness increased due to the forkball grip. In contrast, no significant differences were found between the conditions for the other forearm flexor-pronator muscles.

Conclusions: Quantification of muscle hardness using shear wave elastography showed that gripping a forked ball increased muscle hardness in the flexor digitorum superficialis.