Baseball Pitching Performance

Baseball, a game that has been played worldwide for more than 100
years, involves periods of relative inactivity punctuated by the
highest recorded angular velocities of human movement.

Baseball, a game that has been played worldwide for more than 100 years, involves periods of relative inactivity punctuated by the highest recorded angular velocities of human movement. Pitching, specifically, is considered by many to be one of the most physically demanding movements in all of sports. Professional athletes generate enough kinetic energy to routinely throw in the range of 90 to 100 miles per hour with these forces and torques transferred through the body in milliseconds. This places an extreme demand on the pitcher’s throwing shoulder and elbow, and requires tremendous flexibility, muscular strength, co-ordination and neuromuscular control. When the demands of the throwing task are not met by the static and dynamic restraints of these joints, overuse injury results. Research has shown the shoulder to be the area of the body causing the most disability days among professional pitchers.¹ Common overuse shoulder injuries specific to baseball pitchers are rotator cuff injuries, ranging from acute tendonitis, to degenerative fraying and tearing, impingement lesions on both the anterior (subacromial, subcoracoid) and posterior (internal) aspects, capsular laxity and tightness, and labral fraying and tears.

Recent advances in sports medicine and biomechanics have led to a greater understanding of throwing-related shoulder injuries. For the chiropractor interested in working with the overhead athlete, a thorough understanding of the mechanics involved, combined with injury mechanisms can help maximize performance and minimize injury potential. This article will focus on the physical characteristics of the throwing shoulder and describe some of the adaptive changes that occur and contribute to shoulder injury.

CHANGES IN RANGE OF MOTION
At the most basic level, all throwers exhibit a change in shoulder rotational range of motion (ROM). When assessed in the position of 90 degrees abduction, all throwers demonstrate an increase in external rotation, commonly referred to as glenohumeral external rotation gain (GERG), with a corresponding decrease in internal rotation, referred to as the glenohumeral internal rotation deficit (GIRD).² This has led to the description of the rotational unity rule which states that “an overhead throwing athlete will maintain normal shoulder mechanics if the IR deficit is less than, or equal to, the ER gain.”³ Interestingly, the literature shows that the total ROM is not significantly different between the dominant and non-dominant shoulders; however, in the throwing shoulder this arc of rotation shifts backward, favouring a gain in ER with a loss of IR. This phenomenon has been termed the “total motion concept” and can be attributed to both bony and soft tissue changes.⁴ Pitching performance is enhanced with greater ER as this permits further arm cocking, which has a direct correlation with increasing ball velocity.

BONY CHANGES IN THE SHOULDER
Repetitive pitching has been shown to cause bony changes in the shoulder. Opposing muscle forces acting on the humerus can lead to retroversion of the humerus. This allows for a greater range of ER before the humerus is constrained by the tightening of the capsule and is thought to be prophylactic because it prevents repetitive stress to the capsule and ligaments. Research suggests that retroversion occurs mostly between the ages of 12 and 16, when the growth plates are open.⁵

THE THROWER’S PARADOX
The subtle nuance of the shoulder in the overhead athlete is what has been termed the “thrower’s paradox.”⁴ This states that the shoulder should be lax enough to allow for gains in external rotation (cocking), but should be stable enough to prevent symptomatic subluxation or dislocation. In my experience, all throwers, regardless of age, exhibit some degree of shoulder laxity. This is logical considering the excessive range of motion necessary and has been described as “acquired throwers laxity.” Unfortunately, current research has not been able to delineate what a normal range of laxity may be, and thus a wide spectrum of measurement exists. With respect to injury, there is evidence to show that acquired hyper-laxity, which corresponds to a gradual stretching of the anterior capsuloligamentous structures, can lead to shoulder pathology.6 During the cocking position of maximal external rotation, there is obligate posterior translation of the humeral head that concurrently tightens the anterior structures. With overuse, the anterior capsule stretches allowing the humerus to subsequently translate forward causing the humeral head to contact the upper aspect of the glenoid, producing posterior (internal) impingement of the rotator cuff.⁶

ADAPTIVE RESPONSES
Recently, the concept of Posterior Shoulder Tightness (PST) has been introduced as an adaptive response of repetitive throwing. This consists of both shortening and the development of fibrotic scar formation of the posterior capsule, as well as the posterior rotator cuff. This occurs during the follow-through phase as the rapidly accelerating arm is decelerated by the posterior rotator cuff muscles. Mechanically, this leads to arthrokinematic changes of the shoulder, notably a posterior and superior shift of the humeral head as the tight posterior structures act as a lever.⁷ This results in a gain in ER with a loss of IR and cross body adduction. Research has demonstrated that the acceptable level of IR deficit as a result of PST is 20 degrees.⁸ At or above this level, the shoulder structures can become pathological. This leads to abnormal stresses in both the static and dynamic restraints and has been hypothesized to be a major cause of injuries to the labrum.

There is much debate as to which of the reported adaptations of the overhead shoulder is the main cause of the ER gain and the IR loss and thus, the cause of pitching injury. The literature documents, with certainty, that bony adaptations do occur. From my clinical perspective in working with these athletes, neither acquired laxity or posterior shoulder tightness exists in isolation nor can be labelled as the sole culprit of shoulder injury in pitchers. Due to the repetitive and intense nature of the activity, both occur, to some extent, and must be addressed accordingly, in any therapeutic program to prevent the “shoulder at risk”.⁷ All pitchers whom I work with have regular shoulder “performance” goals that have to be met for continued participation. This includes maintaining appropriate ranges of motion, appropriate muscle firing patterns and neuromuscular efficiency of the scapular muscles, rotator cuff and the prime movers, and maintaining appropriate muscle flexibility. This is accomplished by in-office “performance” treatments as well as a home stretching protocol and strengthening program.

References

1. Conte, S et al. Disability days in major league baseball. AJSM.2001. 29(4): 431-436.
2. Borsa, P et al. Mobility and stability adaptations in the shoulder of the overhead athlete. Sports Medicine. 2008. 38(1): 17-36.
3. Morgan, C. Unpublished data
4. Wilk, K et al. Shoulder injuries in the overhead athlete. JOSPT. 2009. 39(2): 38-54
5. Meister, K et al. Rotational motion changes in the glenohumeral joint of the adolescent/little league baseball player. AJSM. 2005. 33(5): 693-698.
6. Jobe, C. Posterior superior glenoid impingement: expanded spectrum. Arthroscopy. 1995; 11(5): 530-536.
7. Burkhart, S et al. The disabled throwing shoulder: spectrum of pathology Part 1: pathoanatomy and biomechanics. Arthroscopy. 2003. 1994): 404-420.
8. Myers, J et al. Glenohumeral range of motion deficits and posterior shoulder tightness in throwers with pathologic internal impingement. AJSM. 2006. 34(3): 385-391.