Association Between Lumbopelvic Stability During a Single-Legged Step Down and 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: To characterize the predictive ability of lumbopelvic stability on elbow-varus torque during a baseball pitch.

Design: Cross-sectional study.

Setting: Facilities at National Collegiate Athletic Association Division I universities.

Patients or other participants: A total of 44 National Collegiate Athletic Association Division I baseball players (age = 19.6 ± 1.3 years, height = 190 ± 10 cm, mass = 90.1 ± 6.3 kg).

Main outcome measure(s): Pitchers completed a warm-up and then threw 10 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 using a radar gun. Participants also completed a single-legged step-down (SLSD) task with and without a cognitive Stroop, and triplanar pelvic and trunk kinematics were recorded using inertial measurement units. Statistical analysis consisted of a cluster analysis, principal components analysis, and a multivariate logistic regression model.

Results: Cluster analysis identified 2 clusters: low torque-high velocity and high torque-low velocity. The principal components analysis identified 4 patterns of variability (principal components) during the SLSD: (1) sagittal plane, (2) transverse plane, (3) frontal-plane trail leg, and (4) frontal-plane lead leg. Logistic regression models indicated increased transverse-plane trunk (odds ratio = 2.9; 95% CI = 1.1, 8.0; P = .04) and increased pelvis motion (odds ratio = 2.5; 95% CI = 1.1, 6.0; P = .03) predicted higher odds of belonging to the high torque-low velocity cluster.

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 transverse-plane pelvis and trunk motion were independently associated with pitchers in the high torque-low velocity cluster. Our assessment of trunk and pelvis motion during an SLSD provides a method for coaches and clinicians to identify a potential risk factor related to increased elbow-varus torque and decreased ball velocity.