Low-Cost Lower Extremity Screening to Predict Shoulder Distraction Force in College Softball Pitchers

Abstract

Background:

During a windmill softball pitch, the throwing shoulder experiences forces greater than the pitcher’s body weight. Various kinematic, kinetic, and performance factors have been related to shoulder forces and torques in softball pitchers, and softball research has examined clinical screening measures such as range of motion, muscular strength, and/or neuromuscular control. However, no studies have explicitly identified low-cost, clinic-friendly screening measures predictive of shoulder distraction forces in softball pitchers.

Purpose:

To predict shoulder distraction force using low-cost, in-clinic screening measures, including isometric hip rotation strength and trunk mechanics during a single-leg squat.

Study Design:

Descriptive laboratory study.

Methods:

Biomechanical and strength data of 46 collegiate softball pitchers (mean age, 19.8 ± 1.1 years; mean height, 1.7 ± 0.1 m; mean weight, 78.9 ± 11.9 kg) were retrospectively analyzed. Data included shoulder distraction forces captured during a windmill pitch, trunk flexion during a single-leg squat, and isometric hip rotation strength. Subsequently, 4 separate linear regressions with model comparisons were performed to determine if the isometric hip rotation strength and trunk flexion during a single-leg squat could independently predict peak shoulder distraction force after accounting for body mass and pitch velocity.

Results:

The null model, including body mass and pitch velocity, significantly predicted peak shoulder distraction force (P < .001), accounting for 49.9% of the variance. Of the predictors, the isometric drive hip rotation strength ratio was able to significantly predict peak shoulder distraction force beyond the effects of body mass and pitch velocity (P = .015), resulting in a 6.3% increase in variability accounted for (56.2% of the variance of shoulder distraction force).

Conclusion:

The isometric drive hip rotation strength ratio is related to shoulder distraction force and can be used as a low-cost screening measure for collegiate softball pitchers. However, pitch velocity and body mass should also be considered, as these measures accounted for the majority of the variance in shoulder distraction force.

Clinical Relevance:

It is important that screening measures used for softball pitchers consider the multisegment synergy required for pitching and therefore evaluate imbalances and deficiencies associated with the high forces acting on the shoulder. The current study found that collegiate softball pitchers can be proactively screened for greater shoulder distraction forces using isometric hip rotation strength. These findings emphasize to coaches and clinicians the importance of evaluating lower extremity risk factors in upper extremity athletes, and support using a low-cost, low-technology screening measure to identify softball pitchers who are more likely to experience high shoulder distraction forces.