The Throw – From Below: Hip mechanics dictate overhead motion

It’s shoulder and elbow injuries that most often land baseball pitchers and other throwing athletes on the disabled list. But the cause of those injuries often can be traced to strength and flexibility deficits at the hip—effects that reverberate up the kinetic chain.

by Kevin Laudner, PhD, ATC, FACSM

Approximately 58% of all baseball related injuries and 75% of the total time lost from competition are due to injuries of the upper extremity.¹ Although the shoulder and elbow account for the majority of the overall injuries sustained by baseball players, these injuries often stem from dysfunctions occurring away from the injury site. This concept plays out routinely with regard to chronic injuries, especially those involving the lower extremity. For example, patellofemoral pain syndrome often stems from gluteus medius weakness or excessive ankle pronation. These dysfunctions of the hip and ankle result in altered biomechanics and increased stress on the knee, leading to injury. The same concepts can be applied to the upper extremity, especially in the context of activities that require the transference of power generated by the lower extremity to the upper extremity, such as the baseball throwing motion. However, for some reason the effect and role of subsequent joints, specifically those of the lower extremity, are often overlooked in the discussion of injury risk factors in overhead throwing athletes, such as both pitchers and position players in baseball.

Many individuals associate good core strength and flexibility with the abdominal muscles. Although it is important to have strong abdominal muscles for good core function, the largest and often the strongest of the core muscles, such as the gluteal muscles, rectus femoris, and hamstrings, are located at the hip and therefore play a key role in core stability. Unfortunately, the hip muscles are often overlooked, while more emphasis is placed on the abdominal muscles. This is evident among highly skilled baseball players who do not spend the time conditioning the hip musculature during the off season. Often these individuals have tremendous shoulder strength and flexibility, but their hip strength and flexibility are lacking. These deficiencies can be unilateral or bilateral, and can lead to an ineffective transference of potential energy from the lower extremity to the upper extremity during the throwing motion. The athlete then adapts by increasing stress on the upper extremity to generate the force necessary for ball velocity and accuracy. Over time, this may cause micro-trauma to the soft tissue restraints of the shoulder and elbow, such as the inferior glenohumeral ligament and the ulnar collateral ligament, until injury ensues. Reports have shown that 58% of collegiate baseball players complain of shoulder or elbow related pain at some point during their career,¹ while 29% of all days spent on the disabled list among professional baseball players are due to similar injuries.² As such, it is critical that the hip be evaluated for strength and flexibility deficits routinely during preseason physicals and throughout the competitive season. Special attention should also be placed on the role of these hip characteristics during the throwing motion. More specifically, these hip characteristics should be evaluated during the throwing motion to ensure increased stress is not being placed on subsequent joints, such as the shoulder and elbow.

Keeping it off the field

During the throwing motion the body acts as a kinetic chain where forces are transmitted from one joint to another in succession, with the ultimate goal of working together in a sequential pattern to produce a smooth, accurate, and powerful motion. In baseball players, both the upper and lower extremity require good range of motion, strength, and muscle firing patterns to propel the ball with maximum velocity, accuracy, and with the least amount of stress to soft tissue and bony restraints. Deficits observed clinically often translate to what happens biomechanically on the field. Such deficits may initially present as decreased performance in the form of lost ball velocity and control.  Unfortunately, when most players encounter these types of throwing issues, their first instinct is to inform their coach, who in return instinctively recommends more practice. This increased practice tends to accelerate the development of limitations and continues to increase stress on the joints until soft tissue damage occurs. At which point, now that pain is involved, the athlete will speak with a medical professional. But if  this pathological chain of effects could be identified earlier, players could potentially avoid serious injury and drastically reduce the amount of time lost from competition.

As with most athletic motions, the power developed during the throwing motion comes largely from the lower extremity. In baseball players, this power is developed in the lower extremity and then transmitted to the core, shoulder, elbow, wrist, and ultimately to the hand before being delivered to the ball. The throwing motion can be dissected into five phases consisting of the windup, cocking, acceleration, deceleration, and follow through. In assessing the contribution of the hip to this motion, we will examine the biomechanics of the lead leg (the leg on the side opposite the throwing arm) and the trail leg (the leg on the same side as the throwing arm) throughout these phases.

Hip abduction strength

During the windup phase, the body balances on the trail leg as the body begins to rotate away from the intended target in an effort to store potential energy before acceleration. Good isometric hip abduction strength, provided by the gluteus medius of the trail leg, is required during this phase to not only maintain the athlete’s center of gravity over the small base of support available while standing on the trail leg alone, but also to prevent downward tilt of the contralateral pelvis.^3-5 Once the cocking phase begins, the gluteus medius muscles of the trail leg are utilized, although this time concentrically, to begin propulsion of the body forward^3,4 and to optimize stride length as the lead leg is propelled towards the target.^3,4 This leg drive has been shown to be positively associated with arm velocity.⁶ Burkhart et al⁷ hypothesized that poor gluteus medius strength can disrupt the kinetic chain during the throwing motion, thereby placing increased stress on the shoulder. These authors have clinically reported that approximately 44% of their patients diagnosed with SLAP (superior labral anterior-posterior) lesions presented with gluteus medius weakness, as found with a positive Trendelenburg test.⁸ Furthermore, pitchers have been shown to have lower gluteus medius strength in the trail leg compared to position players.⁹ This finding has led to speculation that the decreased hip abduction strength may partially explain why pitchers tend to have more upper extremity injuries than position players. As such, identifying gluteus medius weakness, compared to the opposite limb, during pre-season physical exams and addressing this deficiency may potentially reduce or prevent various upper extremity injuries from occurring over the course of the season. Furthermore, electromyographic data have shown that a side-lying hip abduction movement produces the most activity in the gluteus medius, potentially leading to the largest gains in strength.¹⁰

Rotational flexibility

Not only is hip strength a factor during the throwing motion, but proper hip flexibility is also critical for optimal kinetic chain synchronicity. During the acceleration phase of the throwing motion, the lead foot should contact the ground with the toes pointed approximately towards the intended target. For this to occur, both hips must rotate.  More specifically, the trail leg must internally rotate while the lead leg externally rotates.¹¹ The first sequence in this chain is the trail leg internal rotation. Proper rotation here not only will place the lead leg in an optimal position to externally rotate towards the target, but this rotation also allows the trunk and subsequently the throwing arm to rotate towards the target.^3,12 Research has shown that baseball players tend to have more hip internal rotation in the trail leg than the lead leg,¹¹ and pitchers tend to have less internal rotation of the trail leg than position players resulting in a less effective and potentially more dangerous throwing motion.⁹ If a player lacks the necessary hip internal rotation range of motion to square the body towards the target, the results may cause the player to throw across his body, which would reduce the transfer of power generated from the lower extremity to the upper extremity.^4,12 Research has shown that there is a direct association between increased hip rotation range of motion and increased ball velocity.¹³ Furthermore, Wight et al¹⁴ reported that increased hip rotation results in decreased maximal forces and torques on the throwing arm as the lead leg contacts the ground.

As mentioned previously, good hip external rotation of the lead leg is also vital to the kinetic chain of the throwing motion. More specifically, the lead leg needs enough hip external rotation to position the lead foot at an angle approximately 5^o to 25^o from the midline of the body at foot contact in an attempt to position the lead leg and trunk in direct alignment with the target.⁴ Too much external rotation and the pelvis will rotate leading to decreased trunk rotation.^4,12 Alternatively, not enough hip external rotation and the lead leg will be positioned too close to the midline of the body.^4,12 Regardless, these alterations to hip rotation will lead to a disruption of the kinetic chain and ultimately a loss of energy production^4,12 and possibly an increased amount of force placed on the shoulder and elbow as the athlete attempts to compensate.¹⁴ Therefore, when examining baseball players, specific attention should be paid to the early identification of limited hip internal and external rotation. Furthermore, these limitations should be addressed when returning such athletes to competition after an upper extremity injury. Specific exercises may include stretching the piriformis by moving into a position of hip flexion and external rotation, or by incorporating more functional exercises like diagonal trunk rotations into maximum external rotation and cross body motion.¹⁵

Injury prevention

Throwing related injury prevention programs, evaluations, and rehabilitation programs should also pay attention to these hip characteristics based on the kinetic chain relationship between the hip and the upper extremity. Kibler et al¹⁵ recommends a series of tests to assess the function of the core, such as one-leg standing balance and one-leg squat tests, which require good strength and flexibility of several hip muscles such as the gluteus maximus, medius, and minimus, and well as the rectus femoris and psoas major. Not only do these tests assist in determining deficiencies at the hip, but such movements can also be used to treat these deficiencies. It is also recommended that once good hip strength and flexibility are established, athletes should transition to using exercises that require the development of potential energy in the lower extremity that is then transferred to the upper extremity, much like the demands of the throwing motion. Such exercises may include diagonal trunk rotation, which mimics bending over on one leg to pick up an object on the opposite side of the body, followed by hip and trunk extension, as well as shoulder external rotation and retraction.¹³ This type of full body exercise may assist in programming the muscle firing patterns between the lower and upper extremity.

Although much of the previous research dealing with hip biomechanics in baseball players has concentrated on collegiate and professional level athletes, these guidelines and recommendations may also apply to youth athletes. With the dramatic increases in both shoulder and elbow injuries among these youth athletes, it is clear that similar problems exist regardless of age or skill level.¹⁶ As such, practitioners who work with throwing athletes of all ages are encouraged to address not only dysfunctions in hip strength and flexibility, but also improper throwing mechanics that may be caused by such dysfunctions. This may decrease the number of injuries in youth athletes, as well as older athletes who continue to use improper form that was developed at a younger age.

Based on the role of the hip during the throwing motion it is critical that the hip is evaluated for strength and flexibility deficits routinely during preseason physicals and throughout the competitive season.  Preventative and rehabilitation exercises should also be designed to strengthen and lengthen the various muscles that not only cross the hip, but also contribute to core stability and in the development of potential energy during the throwing motion.

Kevin Laudner, PhD, ATC, FACSM, is an associate professor and director of the Graduate Athletic Training Education Program at Illinois State University in Normal, IL, and the director of research for the Texas Metroplex Institute for Sports Medicine and Orthopedics in Arlington, TX.

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