Relationship Between Stride Mechanics and Shoulder Distraction Force in Collegiate Softball Pitchers

Abstract

Background: Softball pitchers experience high shoulder distraction forces, and increased stride lengths are associated with upper extremity pain. Therefore, it is important to consider the influence of stride mechanics on shoulder distraction force in softball pitchers. Purpose: To determine the relationship between stride mechanics and shoulder distraction force in collegiate softball pitchers. Study Design: Descriptive laboratory study. Methods: A total of 63 collegiate softball pitchers (age, 20.1 ± 1.3 years; height, 173.3 ± 7.4 cm; weight, 79.7 ± 11.7 kg) were included in this study. Each pitcher threw 3 maximum-effort fastballs for a strike, and kinematic data were collected using an electromagnetic tracking system with a sampling frequency of 100 Hz. A forward regression analysis was used to determine the relationship between stride parameters at foot contact (stride length, stride-foot progression angle, and stride-foot position) and shoulder distraction force. Results: Regression analysis revealed a significant and positive relationship between stride length and shoulder distraction force ( R2 = 0.11; F(1, 61) = 7.338; P = .009), where stride length accounted for 11% of the variation in shoulder distraction force. Specifically, shoulder distraction force increased by 0.94 N/kg for every 10% increase in stride length normalized as a percentage of body height. Conclusion: A positive relationship was found between stride length and peak shoulder distraction force during the acceleration phase of the softball pitch. Alternatively, no relationship was found between the other stride parameters (stride position and stride-foot progression angle) and shoulder distraction force. Clinical Relevance: Coaches should be aware of the potential negative implications of increasing stride length during softball pitching. Although prior research has shown that greater stride length may positively affect performance, this may also increase stress at the shoulder.