Lumbopelvic Stability during a Single Leg Step Down Predicts Elbow Varus Torque during Baseball Pitching.

Context: During a baseball pitch, energy is transferred from the lower extremities through the lumbopelvic junction to the upper extremity. Reduced lumbopelvic stability has been associated with elbow injuries, but the mechanisms are unclear.

Objective: Characterize the predictive ability of lumbopelvic stability on elbow varus torque during a baseball pitch.

Design: Cross-Sectional.

Setting: Facilities at NCAA Division 1 universities.

Patients or other participants: NCAA Division 1 baseball players (N=44; 19.6+1.3yrs).

Main outcome measures: Pitchers completed a warm-up and then threw ten fastballs from a mound to a catcher. During the pitches, elbow varus torque was recorded using an inertial measurement unit and ball velocity was recorded with a radar gun. Participants also completed a single leg step down (SLSD) task with and without a cognitive Stroop, while triplanar pelvic and trunk kinematics were recorded by inertial measurement units. Statistical analysis consisted of a cluster analysis, principal component analysis (PCA), and a multivariate logistic regression model.

Results: Cluster analysis revealed 2 clusters: Low Torque-High Velocity and High-Torque-Low Velocity. The PCA analysis revealed 4 patterns of variability (principal components) during the SLSD: 1-sagittal plane, 2-transverse plane, 3-frontal plane trail limb, and 4-frontal plane lead limb. Logistic regression indicated increased transverse plane trunk and pelvis motion predicted higher odds of belonging to the High Torque-Low Velocity cluster; trunk [OR=2.9 (95%CI:1.1,8.0), p=0.036] and pelvis [OR=2.6 (95%CI:1.1,6.0), p=0.031].

Conclusions: Lumbopelvic movement assessed during the SLSD can identify deficits that relate to high elbow torque-low ball velocity during the baseball pitch. Specifically, higher pelvis and trunk transverse plane motion was associated with pitchers in the High Torque-Low Velocity cluster. Our assessment of trunk and pelvis motion during a SLSD provides a method for coaches and clinicians to identify a potential risk factor related to increased elbow varus torque and decreased ball velocity.