Director of Biomechanics Illinois State University, United States
Introduction:: Weighted baseball throwing programs are often used to increase pitch velocity. Findings regarding injury risk of pitching weighted baseballs have been mixed. Analysis of elbow joint angles, reaction force and moments, as well the loading rate and impulse of the forces and moments during pitching of multiple ball weights may provide insight on injury potential. The purpose of this research was to compare the effects of weighted baseballs on elbow joint kinematics and kinetics during pitching.
Materials and Methods:: 10 baseball pitchers (age 13.3 ± 2.69 years, 1.63 ± 0.17 m, 52.29 ± 23.18 kg) were analyzed in this study. The participants threw 5 max effort pitches for strikes with 5oz, 7oz, and 9oz baseballs, and the 3 fastest for strikes were included for analysis. Ball weight order was counterbalanced to remove order bias. Full body, 3D segment position data were collected using a motion capture system at 200Hz. Pitch velocity was recorded using a radar gun (Stalker Radar). 3D marker trajectories were input into a Visual 3D 6DOF model to estimate elbow joint moments and reaction forces using inverse dynamics. Impulse was calculated using R Programming. Varus elbow joint moment, loading rate, and impulse, as well as joint reaction force, loading rate, and impulse were compared with RMANOVA (α = .05) and Fisher’s LSD post-hoc tests (FLSD).
Results, Conclusions, and Discussions:: Differences were noted between ball weights on pitch velocity p < 0.0001 with FLSD post-hoc exhibiting p ≤ .0005 between all velocities (5oz 25.11 ± 4.9, 7oz 23.3 ± 4.5, 9oz 21.8 ± 3.9 m/s). There were no differences found in the elbow flexion angle or peak varus moment (p > .05). Throwing heavier weighted baseballs resulted in decreased peak compressive force p = 0.0007 with FLSD post-hoc exhibiting p ≤ .0445 between all velocities (5oz 439.9 ± 477.9 N, 7oz 393.9 ± 161.3 N, 9oz 354.7 ± 180.3 N), compressive force loading rate p = 0.0004 with FLSD post-hoc exhibiting p ≤ .021 between regulation and 7oz and 9oz, but not between 7oz and 9oz (5oz 10775.5 ± 6569.3 N/s, 7oz 8416.2 ± 5542.5 N/s, 9oz 7619.1 ± 4438.6 N/s), and compression force impulse p = 0.0073 with FLSD post-hoc exhibiting p ≤ .0303 between regulation weight and the heavier balls, but not between 7oz and 9oz (5oz 18.7 ± 6.5 N.s, 15.2 ± 5.4 N.s, 9oz 13.5 ± 5.5 N.s). varus moment loading rate decreased p = 0.0284 with FLSD post-hoc exhibiting p ≤ .0239 between 5oz and 9oz and 7oz and 9oz, but not between 5oz and 7oz (5oz 196.7 ± 123.6 Nm/s, 7oz 199.6 ± 110.3 Nm/s, 9oz 155.1 ± 76.6 Nm/s. Although mass was added to the pitch via ball weights and maximal efforts were recorded, the increased ball weights did not systematically increase moments and forces at the elbow. It is believed that peak compression force and loading rate, as well as the varus loading rate, decreased as a result of the decrease in pitch velocity in the balls thrown with greater mass. Due to the decreases in joint force, loading rate, and impulse, as well as the varus loading rate it can be concluded that heavier baseballs are not more injurious than the competition weight. This suggests that they can be used in a training environment to improve the performance of pitchers without causing a greater risk of injury.
