Abstract
Objectives:
The baseball pitching motion is one of the most complex movements in sports and stresses the elbow joint with substantial amounts of force. Over the past two decades the incidence of elbow injury and the need for surgical intervention in baseball pitchers has been on the rise. This multifactorial problem has stimulated the implementation of pitch count limits, advising against early pitching specialization, and increased the focus on proper pitching biomechanics to improve injury prevention. A majority of pitching biomechanics research has focused on upper extremity kinematics, however research concerning the contribution of the lower extremities to the overall pitching motion requires further understanding. To minimize the risk of injury to the elbow while maximizing performance, a pitcher must be able to efficiently transfer energy through the lower extremities up through their throwing arm. Of particular interest in this paper is understanding the implications of stride position on pelvic rotation, elbow varus moment, and ball velocity.
The purpose of this study was to investigate the affect of stride position and pelvic kinematics on the elbow varus moment and ball velocity in collegiate level pitchers. It was hypothesized that pitchers that land in a crossed-over stride position would reduce their ability to achieve maximum pelvic rotation range of motion, leading to an increase in elbow varus moment and decreasing fastball velocity.
Methods:
Pitchers were recruited from NCAA Division I and Division III college baseball teams and were included in this study if they were actively pitching for their collegiate team. Pitchers were excluded if they had experienced an injury that caused them to miss one game or practice within the preceding 6 months. Each participant pitched a total of seven of each pitch type they were comfortable throwing in a game setting from a regulation indoor mound towards a pitching target 60 feet 6 inches away. Data for this study were limited to fastball data only. Motion data were collected at 250Hz using a 12 camera Vicon 512 motion analysis system (Vicon, Oxford, UK). Kinematic data were calculated using a 16- segment biomechanical model based on Euler’s equations of motion, and upper extremity joint kinetics were calculated using standard inverse dynamic techniques. Stride cross-over was defined as when the pitcher’s lead stride foot landed more towards third base if they were a right-handed pitcher or more towards first base if they were a left-handed pitcher (Figure 1). Other predictor variables included pelvic angular velocity (°/sec), pelvic rotation at ball release (°), and pelvic range of motion (°). Statistical analyses were performed using a mixed effects random intercept regression model to determine associations among the variables of interest.
Results:
A total of 99 baseball pitchers were recruited with a mean age of (20.7 ± 1.3 years), height of (1.8 ± 0.7 m), and weight of (88.6 ± 13.5kg). No pitchers were excluded from this analysis.
Regression analysis demonstrated that for every 100°/sec increase in pelvis angular velocity the elbow varus moment increased by 5.6Nm (p=0.00) and ball velocity increased by 0.43mph (p=0.00).
Additionally, it was noted that for every 10° increase in pelvis rotation at ball release and 10° increase in total pelvic range of motion, the elbow varus moment increased by 0.4Nm and 0.2Nm respectively (p=0.036, p=0.02) and ball velocity increased by 1.8mph and 1.1mph respectively (p=0.03, p=0.01).
Pitchers that achieved greater pelvis range of motion experienced a 0.26% increase in elbow varus moment accompanied by a 1.6% increase in ball velocity. Additionally, pitchers that demonstrated greater pelvis rotation at ball release experienced a 0.53% increase in elbow varus moment and 2.55% increase in ball velocity.
Although not statistically significant a quartile analysis demonstrated that pitchers who landed in a cross-over stride position had the largest elbow varus moments accompanied by relatively low-ball velocity compared to pitchers that landed in an open stride position, who tended to have low elbow varus moments with relatively high ball velocity (Figure 2).
Conclusions:
The results of this study indicated that stride position during pitching was associated with both elbow varus moment and ball velocity. Pitchers that landed in a more crossed-over position experienced greater elbow varus moment and lower fastball velocity compared to those that landed in an open stride position. It is theorized that an open stance stride position allowed the pelvis to achieve full range of motion, thus leading to an efficient energy transfer to the throwing arm. This was supported by the finding that pitchers who achieved greater pelvic range of motion experienced smaller elbow varus moments compared to pitchers with less pelvic range of motion. Additionally, pitchers who demonstrated greater pelvic rotation at ball release and greater pelvic range of motion experienced an almost two mile per hour and one mile per hour increase in fastball velocity, respectively. These results can aid pitching coaches and trainers in understanding the implications of incorrect lower extremity pitching mechanics on elbow injury risk reduction and performance in baseball pitchers.
