Differences in Pitch Kinematics Between Youth and Professional Baseball Pitchers

Abstract

PURPOSE: To compare the youth pitching biomechanics with that of elite adult pitchers and to identify differences that might explain common injuries seen in youth pitcher populations. METHODS: Twenty-five professional and 14 youth baseball pitchers were filmed at 120 Hz using two high-speed video cameras. The locations of 21 body landmarks were digitized and their three-dimensional locations were calculated using the DLT method (Abdel-Aziz & Karara, 1971). Three-dimensional position data were filtered using a fourth order Butterworth filter with a cutoff frequency of 13 Hz. From the marker coordinates, the kinematics of the pitching elbow and shoulder were calculated using a standard technique (Fleisig et al., 1996; Werner et al., 1993). Kinematic data were normalized in time to facilitate comparisons and so group mean values could be calculated. RESULTS: The peak shoulder internal rotation and elbow extension angular velocities of the youth pitchers were greater than those of the professional pitchers. Peak shoulder external rotation in youth pitchers was 166 +/− 9 degrees, compared with 182 +/− 13 degrees in professionals (p<0.001). The most striking difference between the groups was in trunk motion. The peak rotational velocities of both the upper trunk and pelvis were greater in youth baseball pitchers than in professional pitchers. Peak upper trunk rotational velocity was 2102+/− 324 deg/s in youth pitchers and 1193 +/− 176 deg/s in professional pitchers (p<0.001). CONCLUSIONS: The data support the observation that youth baseball pitchers control their trunk motion in a less efficient way than elite pitchers (Ireland & Hutchinson, 1995). Peak pelvis rotation velocity occurred near the time of stride foot contact in the professionals, while it occurred much later in the youth pitchers. Proper timing of pelvis and upper trunk rotation are necessary to effectively transfer energy from the trunk to the throwing arm (Fleisig et al., 1996). Therefore, increased trunk rotational velocity may be a compensation for improper timing of segment rotations or insufficient muscle strength in youth pitchers. Improper energy transfer from the trunk to the upper extremity may lead to the increased shoulder internal rotation and elbow extension velocities in youth pitchers compared to the professionals.