Lead and Back Hip Flexion-Extension Excursion: A Biomechanical Analysis in High School Baseball Pitchers.

Background: Relationships between the back leg's lumbopelvic control and throwing arm kinetics have been established in throwing athletes. However, little literature has established normative values for in-pitch hip flexion parameters as well as the role that hip flexion-extension excursion may play in the generation of throwing arm kinetics and ball velocity.

Purpose: (1) To establish normative values for lead and back hip flexion for high school (HS) pitchers and (2) to investigate the relationship of lead and back hip flexion-extension excursion with throwing arm kinetics, full body kinematics, and ball velocity.

Study design: Descriptive laboratory study.

Methods: A total of 56 HS pitchers, who were instructed to throw 8 to 12 fastball pitches, were evaluated with 3-dimensional motion capture. The mean normative values of lead and back hip flexion-extension excursion were calculated and compared with an internal database of professional pitchers for comparison. HS pitchers were then divided into quartiles based on "high" and "low" lead and back hip flexion-extension excursion. Multiple regression models examined the association of lead and back hip excursion, controlling for anthropometric parameters, with ball velocity and throwing arm kinetics.

Results: HS pitchers had decreased lead hip (43°± 14° vs 48°± 14.6°, respectively; p = .038) and back hip (50°± 18° vs 56°± 15°, respectively; p = .009) flexion excursion compared with professional pitchers. Pitchers with low lead hip and low back hip excursion also had significantly less shoulder internal rotation torque (3.5%BW × BH vs 4.5%BW × BH and 4.4%BW × BH, respectively; P _max = .03), shoulder anterior force (30.4%BW vs 36.3%BW and 35.8%BW, respectively; P _max = .03), elbow varus torque (3.3%BW × BH vs 4.3%BW × BH and 4.2%BW × BH, respectively; P _max = .02), and elbow medial force (27.1%BW vs 35.5%BW and 34.1%BW, respectively; P _max = .03) compared with pitchers with high lead hip and high back hip excursion as well as pitchers with high lead hip and low back hip excursion. When controlling for anthropometric parameters, lead and back hip excursion were not strongly predictive for ball velocity (P > .05). Only back hip excursion was moderately predictive for shoulder anterior force (P = .04; B = 0.118 [confidence interval 0.006-0.230]; β = 0.272).

Conclusion: HS pitchers had less lead and back hip flexion-extension excursion compared with professional pitchers. Lead and back hip flexion-extension excursion likely play small roles in ball velocity for HS pitchers; however, increased back hip flexion-extension excursion may be a risk factor for higher shoulder anterior force.

Clinical relevance: Establishing normative values for hip flexion excursion in HS pitchers provides clinicians, coaches, and strength and conditioning professionals with important benchmarks for assessing lower body mechanics during pitching. The identification of reduced lead and back hip flexion excursion in HS pitchers compared to professionals highlights a potential developmental gap that may influence throwing arm kinetics. Although hip flexion excursion appears to have minimal impact on ball velocity, increased back hip excursion was associated with higher shoulder anterior forces, suggesting a possible risk factor for shoulder load. These findings can inform targeted training interventions to improve lower body mechanics, reduce upper extremity loading, and ultimately contribute to safer pitching practices for developing pitchers.