Biomechanical analysis of forearm pronation and its relationship to ball movement for the two-seam and four-seam fastball pitches.

This study examined forearm pronation in relation to both the vertical and horizontal ball movement measured for 2 variations of the fastball pitch. Ten healthy collegiate baseball pitchers participated in the study (age: 19.4 +/- 0.7 yr, height: 1.90 +/- 0.06 m, mass: 88.50 +/- 9.05 kg). Reflective markers were placed at the level of each joint center's location, and standard high-speed video techniques were used to record the participants as they threw 10 maximal effort fastball pitches. Marker positions were digitized in each video frame from which forearm pronation data were calculated. Across all pitchers, magnitude of both the vertical and horizontal ball movement was observed to be greater for the 2-seam fastball than for the 4-seam fastball. Regardless of pitch type, positive relationships were observed between all forearm pronation parameters and both vertical and horizontal ball movement. A significant positive correlation (r = 0.583, p < 0.01) was identified between forearm pronation acceleration at ball release and the magnitude of vertical ball movement regardless of pitch type. These results suggest that pitchers may be able to manipulate the magnitude of vertical ball movement by altering pronation accelerations at ball release. In addition, it appears that pitchers should alter their current training techniques so as to increase the endurance capabilities of the primary pronator muscles of the forearm. In doing so, they may be able to limit the effects of fatigue on these muscles during pitching, thus preventing a decrease in the magnitude of vertical ball movement that typically occurs late in a pitching performance.