Baseball - Throwing Mechanics

Shoulder Abduction and Lateral Trunk Tilt Influence the Peak Elbow Varus Torque During Pitching

Matsuo T, Fleisig GS, Zheng N, Andrews JR. Simulated influence of shoulder abduction and lateral trunk tilt on peak elbow varus torque for college baseball pitchers. Journal of Applied Biomechanics 22:93-102, 2006

Methods

Varus torque is a primary factor in the risk of elbow injury during pitching and it was hypothesized that varus torque may be affected by shoulder abduction angle and lateral trunk tilt angle. Motion data of 33 healthy, college baseball pitchers were collected at ASMI and used for computer simulation in which shoulder abduction and lateral trunk tilt angles were systematically altered from the actual movement. For each pitcher, 42 simulated motions were generated and the peak elbow varus torque for each motion was calculated.

Results

The main effect of shoulder abduction angle on peak elbow varus torque was found to be significant (p<0.0001). The results showed minimum peak elbow varus torque at 90º and 100º of shoulder abduction. The main effect of lateral trunk tilt was also found to be significant (p<0.0001). The minimum in peak elbow varus torque was found to be at 0º of lateral trunk tilt. Finally, the interaction of shoulder abduction angle and lateral trunk tilt was also significant. The combination of 10º of lateral trunk tilt and 100º of shoulder abduction produced the minimum peak varus torque among all conditions in the study. Thus, the results of this simulation study clearly show that shoulder abduction angle and lateral trunk tilt have an affect on elbow varus torque and thus can be helpful in reducing stressful forces on the shoulder and elbow during pitching.