April 2016

Shoring up the rotation: The importance of hip mechanics in pitching

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Over the course of a season, collegiate pitchers undergo changes in hip rotational range of motion and hip strength—changes that could increase injury risk or negatively affect performance.

By Giorgio Zeppieri Jr, MPT, SCS, CSCS

The baseball pitching motion is a multifaceted sequence of movements that requires the production and transfer of energy from the lower extremities through the trunk and upper extremity to achieve ball velocity.1-5 Due to the repetitive nature of this motion, pitchers are highly susceptible to injury during the course of a competitive season. Specifically, decreases in hip range of motion (ROM) and strength can alter pitching mechanics so that abnormal stresses act on the trunk, glenohumeral joint, and elbow.1,3,6-8 These stresses can influence pitching performance and increase injury risk in this patient population.

Mechanics of pitching

The pitching motion and its biomechanical components have been widely defined and are divided into six phases: windup, early cocking/stride, late cocking, arm acceleration, arm deceleration, and follow-through.9-14 Efficient maximization of this kinetic motion involves the proper utilization of the lower extremities and core in conjunction with the upper extremities to reduce primary reliance on the dominant shoulder to generate ball velocity.9-14 Operationally, we define the leg ipsilateral to the throwing shoulder as the “trail leg” and the leg contralateral to the throwing shoulder as the “lead leg.”

The pitching motion is initiated with the windup (setting phase) and occurs when the pitcher’s weight (center of gravity) is transferred toward and over the trail leg as the lead leg is flexed at the knee and hip, initiating pelvic rotation and lumbar flexion.3,9,14,15

The early cocking/stride phase occurs as the throwing shoulder begins to maximally externally rotate. The lead knee and hip begin to extend and medially rotate while the trail knee and hip flex to allow for pelvic rotation, trunk stabilization, and lowering the body’s center of gravity.9,14

During the late cocking phase, the lead foot lands in slight internal rotation (IR) and in line with the trail foot, the throwing shoulder is maximally externally rotated and in line with the nonthrowing shoulder, the trunk is tilted toward the nonthrowing shoulder and slightly hyperextended, and the pelvis is rotated.9,14,16,17

After the shoulder achieves maximum external rotation (ER), the pitcher accelerates the throwing arm forward by either driving off the trail leg by extending and externally rotating the trail hip or rotating around the lead leg similar to a tethered ball.3

When the ball is released, the lead hip flexes and internally rotates to decelerate the throwing arm and move the body forward, as well as to absorb the distraction forces occurring at the throwing shoulder.3,9,14,16-18

Lastly, during the follow-through, the trunk, lead knee, and lead hip continue to flex to disperse the forces created during ball acceleration.9,14,16,19,20

Given the important role of the lower extremities in all phases of the pitching motion, a disruption in any of these lower extremity biomechanical contributions, specifically hip ROM and strength, will cause an accumulation of abnormal stress along the throwing shoulder, elbow, and lumbar spine.

Pitching and hip rotation

4Cover-shutterstock_88032553Restrictions in hip rotational ROM (IR and ER) in both the lead and trail hip have been shown to influence pitching mechanics and injury.1-3,20 For instance, decreased hip IR and subsequent increased ER in the trail leg during arm cocking and acceleration are associated with increases in lumbar extension, glenohumeral ER, and elbow valgus, which may lead to increased stress along the pars inter­articularis, labrum, and ulnar collateral ligament.1,3,8,15,20,21

Additionally, inadequate or excess lead hip ROM (restriction or surplus of IR or ER) during arm acceleration through ball release will cause early pelvic rotation, attenuating force production and transfer, as well as decreasing the ability of the lower extremities to absorb forces.1,3,15,21

Furthermore, restrictions in lead hip ROM (IR or ER) will change lead-leg foot placement, causing the lead foot to land either “open” or “closed.” This will attenuate the force transfer from the lower to upper extremities and cause a decrease in velocity, increased valgus load on the elbow, and increased stress on the glenohumeral joint.22 The inability of the lower extremities to absorb force will cause the rotator cuff to contract eccentrically to absorb those forces in order to decelerate the arm; this may cause stress at the glenohumeral joint and medial elbow.3,8,15,20,23-25

The majority of collegiate pitching-related injuries occur at the shoulder, with rotator cuff tendonitis documented as the most common upper extremity injury.26-28 Additionally, at this level, upper extremity injuries are responsible for the most time lost from sports participation.28 Most injuries occur during the season and may result from a breakdown in proper pitching mechanics due to inadequate recovery, increased pitching frequency, or increased pitching workload.29 Regardless, it is imperative to monitor pitching mechanics during the season. Pitchers are vulnerable to the increased demands of the competitive season, which may fracture the timing pattern of the pitching motion, negatively increasing the stress on upper extremity structures.29,30

Prior studies have examined changes in hip ROM and isometric strength as potential injury risk factors, but it is not known if these changes occur over the course of a season and whether they are a result of pitching workload.4 Despite the evidence describing the importance of hip rotation ROM and strength while pitching, there are few descriptive data detailing the change of hip rotation and strength profiles due to pitching workload over the course of a season in Division I baseball pitchers; we conducted a study to address this information gap.4

Our research

The primary goal of our study was to identify changes in hip ER ROM, hip IR ROM, total rotational arc of motion, isometric hip abduction, and hip extension strength in pitchers during a competitive season and to determine the association among changes in hip ROM, strength, and pitching volume (number of pitches during a season).4

Fourteen Division I collegiate baseball pitchers consented to participate in our study. Nine were right-hand dominant and five were left-hand dominant. We tested all participants twice: once prior to the beginning of the season before preseason workouts and again at the end of the postseason (Super Regional) play, which totaled 66 games over five months.4 The University of Florida coaching staff in Gainesville documented the individual pitching workload of each participant (calculated by the number of pitches thrown during each game) over the course of the season.4

Our study showed pitchers’ trail and lead hip ER, hip IR, and total rotational ROM decreased over the course of a competitive season, but only trail and lead hip ER and total rotational ROM were statistically significant.4 We hypothesize that the repetitive landing with the lead hip internally rotated (causing restrictions in lead hip ER that may alter stride length, lead-foot placement, and lead-knee flexion angle) in the late cocking phase and posting over the trail hip in IR in the windup phase may result in an overall decrease in bilateral hip ER, which would contribute to the overall decrease in total hip rotational ROM.4,22 The excessive positioning of the trail hip into IR while driving and initiating the pitching motion may be the cause of adaptations restricting hip ER during the acceleration phase.

4Cover-iStock57867006In addition to changes in hip rotational ROM, a decrease in hip abduction strength and hip extension strength may lead to faulty sequencing of force from the lower extremities to the upper extremities, which may place an increased load on the upper extremity to produce force when pitching.1,4,31 This essentially causes the pitcher to become more of an upper-body thrower rather than a whole-body pitcher, leading to an increased risk for upper extremity injuries and diminished performance.1,4,31,32

To further illustrate, during the wind-up and arm-cocking phase, trail hip abductors will fix the pelvis and, along with the hip extensors, initiate the forward movement of the pitcher while he is striding toward the batter.1,4,7,11,21,25,33,34 An inability to do this will cause the pelvis to drop, impeding the forward movement of the pitcher and reducing the length of the pitching stride.1,4,11,21,33 This unfavorable consequence will shift the burden of generating force from the lower extremity to the upper extremity, negatively influencing ball velocity and increasing stress on the labrum, posterior capsule, rotator cuff, and medial elbow.1,4,20,31,32 Additionally, during the late cocking and acceleration phase, lead hip abductors and extensors act to stabilize the lead leg to increase the forward motion and rotation of the trunk and upper extremity.22,32  An inability to do this will cause a break in the transfer and development of force due to a decrease in trunk rotation, causing a decrease in velocity, as well as an increase strain on the anterior shoulder, rotator cuff, and medial elbow.22,32

Our findings demonstrated that both lead and trail hip abduction strength and extension strength decreased during the season; however, those decreases were statistically significant for only lead and trail hip abduction strength.4 Although these changes may have occurred because of the repetitive nature of pitching and the associated muscular fatigue that occurs over the course of a game or season, we cannot discount other possible contributing factors, such as the decrease in time spent weight training during a season or anthropometric factors.

The changes that occur over the course of a season may be attributed to many causes. We hypothesized that one explanation may be pitching workload (number of pitches thrown over the course of a season). To date, no study had looked at the influence of pitching workload on changes in hip ROM and strength; however, differences between pitchers and position players have been looked at cross-sectionally by Laudner et al.1 In their study, pitchers were shown to have less hip rotation ROM and strength than their position-player counterparts.1

There could be many explanations for these differences; however, one obvious difference between pitchers and position players relates to overall throwing volume. The repetitive motion of pitching—which has been reported to occur between 200 to 1500 times over the course of a season35 in addition to normal flat-ground long tosses—was hypothesized to predispose pitchers to lower levels of hip ROM and muscular fatigue. Our finding that changes in hip ROM and strength were not significantly associated with pitching workload does not support this hypothesis.4 However, we considered only in-game pitching volume and not overall pitch count, which includes pitching in practice and before games. Therefore, we may have underestimated total seasonal pitching volume.

Clinical implications

4Cover-shutterstock_97678301Our findings indicate that, over the course of a season, collegiate pitchers are undergoing changes in hip ROM and strength—specifically decreases in hip ER, hip IR, total rotational ROM, hip abduction strength, and hip extension strength. Although we are not implying a cause-and-effect relationship, these changes may be an indicator of increased injury risk or decreased performance. However, future research is needed to determine if these changes are predictive.

Based on our findings and the emerging literature regarding the importance of lower extremity strength and ROM in pitching performance and injury prevention, it is essential to implement an off-season and in-season training program directed at increasing lower extremity strength and power, while preserving and enhancing lower extremity flexibility. Anecdotally, we find that incoming college players tended to demonstrate poorer strength and flexibility measures compared with their upper-classman counterparts. This, combined with the increased performance demands at the collegiate setting and increased game and practice schedules, increases this population’s susceptibility of injury. Additionally, college pitchers with poorer lower extremity strength measures demonstrate lower ball velocity on average. This is not only evident in our population, but in other college pitching populations and settings.33

An awareness of lower extremity function during the pitching motion as well as subsequent changes that can occur over a season can aid in developing preventive, rehabilitative, and performance programs to improve athletic performance and screen for potential injury risk in this population.1,9 Specifically, we recommend routine in-season monitoring of hip ROM and strength by physical therapists, trainers, and strength and conditioning coaches to maintain preseason values.

Giorgio Zeppieri Jr, MPT, SCS, CSCS, is the UF Health Rehab Center—OSMI clinical research chair and a physical therapist specializing in sports and overhead throwing athlete rehabilitation at the University of Florida Orthopaedic and Sports Medicine Institute in Gainesville.

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