This is the second article in a 2-part series that highlights injury prevention programs specific to the overhand throwing athlete. In the first part, we identified valgus strain as the primary etiology responsible for medial elbow injury. To counter the valgus stressors, the flexor-pronator muscle (FPM) group act to dynamically stabilize the elbow and protect the ulnar collateral ligament (UCL) from tensile overload. Stability, however, may be compromised because of dynamic muscle fatigue stemming from overuse over the season, which predisposes pitchers to greater risk of injury. From an injury prevention perspective, we introduced the “Pitchers' Baseball Bat Training Program,” a new preventive training initiative that may serve to better protect the UCL from tensile overload. The intention is to reduce both risk and severity of medial elbow injury by enhancing tensile strength, neural drive, and recoverability of the FPM.
In this second part, we describe functional and contraindicated shoulder exercises to alleviate valgus stress by improving throwing arm mechanics throughout the kinetic chain of the upper extremities. In reviewing the literature, post-pitching exercises concentrate primarily on rotator cuff and scapular conditioning but do not specifically address varus-valgus stability. Axioscapular, axiohumeral, and scapulohumeral muscle function is essential for mechanical leverage and to accelerate and decelerate the throwing arm, but elbow health specific to training has generally been neglected. Players who are either overtrained or in a state of deconditioning often experience proximal muscular imbalance, inefficient force production, and increased laxity, all of which promote medial elbow injuries (3,4,18–23,28,29).
Guidelines currently being advocated for preventing elbow injuries among youth baseball pitchers are summarized in Table 1, with the focus on managing pitch type, frequency, and accumulation (11–16). Strengthening the shoulder and elbow, although not identified, is integral to healthy throwing arm function and may assist in reducing elbow valgus stress during the kinetic chain of events, from late-cocking to follow-through or otherwise known as the “critical instant” of the pitching delivery. Key biomechanical events of interest include (a) maximal external shoulder rotation (MER), (b) maximal external shoulder rotation moment (MER-M), (c) maximal internal shoulder rotation moment (MIR-M), and (d) peak elbow extension velocity (EEV). Strengthening the shoulder internal rotators and elbow flexors may better regulate acceleration and deceleration of the throwing arm during the critical phase and subsequently restrain the pathomechanics that exacerbate medial traction (tendinopathies, neuropathies, ligamentous ruptures), lateral compression (high force radiocapitellar contact), and posteriomedial shear (osteophyte formations) injuries to the elbow.
THE THROWING ARM KINETIC CHAIN AND PITCHING VELOCITY
Respective peak angular throwing arm and ball velocities are related to the pitchers' linked force system, commonly referred to as the kinetic chain (12,27). The kinetic chain is a sequence of intersegmental energy transfers throughout acceleration and deceleration of the segments (rigid bodies) until follow-through. The kinetic chain is initiated through frictional and vertical ground reaction forces imparted onto the foot by the ground, baseball cleat traction, and pitching mound elevation. During overhand throwing, interactive joint moments transition through the kinetic chain, beginning with the lower body and proceeds through trunk rotation and culminates at ball release. Using coordinated eccentric muscular contractions about the scapula, humerus, forearm, and wrist during arm cocking, the transfer of elastic energy augments concentric muscle force in accelerating the throwing arm to achieve the highest kinetic energy at the throwing hand. The highest hand velocities at ball release are associated with high magnitudes of MER, MIR-M, and peak EEV (8,9,13,17,27).
VALGUS STRESS IMPLICATIONS AND MAXIMAL EXTERNAL ROTATION AT THE SHOULDER
Greater external shoulder rotation is reportedly correlated with higher ball velocities, yet can exacerbate valgus stress. As such, exercises that promote MER flexibility offer both benefit and contraindication. With overhand throwing, external shoulder rotation traditionally increases where internal shoulder rotation decreases because of collective ligamentous, tendinous, and capsular adaptations (anterior laxity and posterior capsule tightness). This condition is commonly known as glenohumeral internal rotation deficit (GIRD).
GIRDs are caused by posterosuperior shifts of the humeral head about the glenoid fossa, which mediates greater shoulder external rotation and exacerbates anterior capsule and muscular laxity (3,28). Greater external rotational instability predisposes one to greater risk of developing superior-labral-anterior-posterior lesions, owing to valgus stress overload. Humeral torsion (axial counter-rotation between the proximal and distal ends) increases with greater degree of external shoulder motion and reduced eccentric bracing because both combine to increase inertial effects of the forearm (1,24,26). Increased forearm inertia places greater demand on the elbow's dynamic stabilizers. As described in Part I, varus torque stabilization offloads the UCL when accelerating the forearm forward during pitching delivery. Pitchers with advanced degrees of MER may also benefit from varus torque stabilization training. By improving shoulder mechanics and contractile function, valgus magnitudes and loading rates may be further attenuated. The evidence from sports biomechanics research supports this, given positive correlations between horizontal abduction and external rotation velocities at the shoulder have been shown to increase magnitudes of elbow valgus stress.
The association between MER and medial elbow injuries is unavoidable because capsularligamentous stretch (creep) stemming from repetitive stresses, and ensuing laxity, allows greater internal shoulder rotation velocities, and consequently ball release velocities, but to the detriment of the elbow (27). MER dysfunction, however, can be managed conservatively by integrating resistance training that targets the shoulder with kinematic analysis of pitch delivery and functional range of motion assessments (ROMA). GIRD may be alleviated by implementing the sleeper stretch to promote post-game recovery within 24-hours post-pitching. The sleeper stretch ROMA involves the person lying on their side with the scapula stabilized against the ground, while the examiner positions the humerus in approximately 90° shoulder flexion and the elbow flexed 90°. The forearm is then progressively moved through inward rotation (towards ground) until terminal range of motion is achieved. Glenohumeral internal rotation is interpreted as the angle between the moveable and stationary arms of the goniometer while in the sleeper stretch position. The movable arm should be aligned with the ulnar styloid through the line of the olecranon (Figure 1).
Traditional internal rotation ROMAs are performed with the person lying supine with their shoulder abducted 90° and horizontally adducted 10° toward the scapular plane. Two evaluators are required, one to obtain goniometric measures and the other to stabilize the scapula. Observed internal rotation deficits between the dominant and nondominant arm of 20° or more may be indicative of GIRD or other related pathomechanics. Regular post-game assessments are advocated because a single comparison between preseason and postseason measures may not be sensitive enough to detect GIRD. Repeated measures enable persons to respond better to shoulder dysfunction at the outset, thereby minimizing joint mobility complications and ultimately preventing injury.
Although the long-term impact of the sleeper stretch on range of motion deficits remains unknown, it is easily performed and the opportunity for daily assessment may warrant its use as a general injury prevention strategy. If any pitcher exhibits internal rotation deficits greater than 10° in their dominant shoulder after preseason screening, then active capsular stretching is warranted. The active sleeper stretch is like the sleeper stretch, only the posterior capsule is dynamically stretched to promote joint mobility. With the subject positioned similarly to the sleeper stretch, the trainer gently pushes the forearm forward to further internal shoulder rotation until a gentle stretch in the posterior-shoulder capsule is sensed. Five sets of 20-second holds are recommended for each arm. For persons experiencing mobility restrictions, treatment protocols are practiced as prescribed by medical professionals.
VALGUS STRESS IMPLICATIONS AND EXTERNAL ROTATION TORQUE AT THE SHOULDER
Three dimensional motion analysis of the throwing arm have estimated angular velocities to be around 7000°/s for internal shoulder rotation and 3000°/s for elbow extension. Coordinated muscular action required to accelerate the throwing arm is first initiated by stored elastic energy being released from the internal shoulder rotators. Concentric recruitment of the elbow extensors follows whereupon these synchronized actions maximize hand velocity during the critical instant of pitching. The MIR-M, being the resultant rotary force axially rotating the humerus toward home plate, is supplied by the subscapularis, teres major, pectoralis major, latissimus dorsi, and the anterior deltoid (Figure 2).
At the critical instant, the shoulder undergoes passive external rotation, reaching a maximum of 150–180°, with concomitant elbow flexion continuing from 85° to 105°. Thereafter, the throwing arm accelerates toward home plate reaching 105–115° external shoulder rotation and 20–38° elbow flexion at ball release. During this phase, the elbow transitions from a varus to a valgus torque, beginning from MER of the shoulder (highest valgus stress) to maximal internal rotation (increased varus stress), which compresses the respective medial and lateral elbow compartments. Valgus stressors acting on the elbow at the precritical instant (stride foot contact to MER) are known to predispose pitchers to injury. At the critical instant, the humerus undergoes axial torsion (counterrotation about the proximal and distal ends) as the forearm lags behind the upper arm. To oppose the inertial properties of the forearm lag at MER, varus moments accelerate the forearm toward home plate. Valgus stress injuries that precede the critical instant have been positively correlated to higher MER-M. Eccentric loading of the humeral internal rotators combined with passively stretching the joint capsule controls MER-M, external shoulder rotation velocity, and excursions (joint position) from late arm-cocking to acceleration. By training the humeral internal rotators eccentrically, tissue elasticity may be augmented, which in theory may reduce pitching effort and decrease concentric effort in both MIR-M and MER-M while producing the highest hand velocities.
Appropriate warm-up before eccentric training should be monitored by qualified training personnel. This is to ensure correct technique in refining neural muscle responses, reducing tissue viscosity, and acclimatizing capsuloligamentous and musculotendinous units to tensile stress. By abducting the shoulder between 75° and 80° for training exercises, scapular stabilization strength and scapulohumeral coordination are improved while the risk of subacromial impingement syndrome is reduced.
Standing eccentric internal rotation cable exercise: In an upright lunge stance, position the humerus slightly below the throwing arm slot position, approximating 80° shoulder abduction, neutral trunk position, and 90° elbow flexion (Figure 3). The strength coach assists with moving the shoulder into the internally rotated starting point, with the hand grip placed at the level of the athlete's chest or just below and the cable parallel to the floor. The strength coach spots the eccentric component of the lift that terminates when the shoulder is externally rotated approximately 90°, that is, with the forearm perpendicular to the floor (Figure 4). Moving into shoulder external rotation, the athlete should begin using the lightest setting (usually 10 lb on most cross cable stands) and progressively increase (using the smallest increments) while adapting to resistance over 3 sets.
Begin supine internal rotation eccentric exercises with the person lying supine on the ground, knees bent, and feet flat on the floor. The upper arm is positioned with the shoulder abducted approximately 80° and the elbow flexed 90° to mirror the arm slot position. With the knuckles facing upward (considered 0° internal rotation and the forearm perpendicular to the ground), the strength coach stabilizes the scapula to focus eccentric rotator cuff and internal rotator activation while the weight is lowered (Figure 4). The repetition is completed when the dumbbell contacts the floor at approximately 90° of external shoulder rotation. Successive repetitions commence after the strength coach assists in returning the weight to the starting point (0° internal shoulder rotation). Minimal muscular effort is required when returning the weight to the starting position, with emphasis solely on eccentric lowering of the weight (Figures 5, 6).
Eccentric activation of the internal shoulder rotators is thought to improve MIR-M and reduce elbow injury susceptibility during the amortization phase (the transition from eccentric to concentric contraction) (1,26). The MIR-M functions to first decelerate MER and then accelerate internal rotation of the proximal humerus. Efficient MIR-M has the capacity to reduce elbow varus stabilization requirements to accelerate the forearm to ball release, lowering valgus stress magnitudes.
Throwing arm injuries arising from muscular fatigue during repeated baseball pitching have been associated with reduced eccentric strength and tissue recovery capacity. Eccentric training may perhaps diminish fatigue-induced insult by promoting tissue growth and enhancing tensile strength, as both have been shown to reduce microtrauma severity (25). Microtrauma brought on by cumulative tensile stress exacerbates tendinopathies, neuropathies, and ligamentous tears. Post-pitching pain, inflammation, and muscle damage biomarkers have also been reduced with regular eccentric contractions (20,21).
VALGUS STRESS IMPLICATIONS AND MAXIMAL INTERNAL ROTATION TORQUE AT THE SHOULDER
Strengthening the internal rotators concentrically is equally important, given the inverse relationship between valgus stress and MIR-M (1,2,5,7,24,26). Muscular fatigue aggravates MIR-M, where humeral internal rotator strength deficits alter throwing mechanics. The compensatory mechanics and insufficient recovery of the internal rotators collectively exacerbate shoulder injury and elbow injury risk. In post-game assessments of shoulder fatigue using handheld dynamometry, Mullaney et al. (18) observed a 20% loss in internal shoulder rotation strength. Strength losses were associated with internal rotation deficits attributable to inflammation and capsular contractures, thereby keeping the shoulder in greater degree of external rotation.
Banded internal rotation to pronation requires an elastic resistance band to be tethered at shoulder height behind the individual (Figure 7). Begin with the shoulder positioned in 80° abduction and 90° externally rotated, with the elbow flexed to 90°. This exercise demands concentric activation of the internal shoulder rotators, elbow extensors, and flexor-pronator mass muscles to slowly internally rotate the shoulder, extend the elbow, and pronate the forearm and wrist. The hand completes the throwing movement, which culminates at the eyebrow level. Slowly return to the starting position for subsequent repetitions (Figures 7, 8).
VALGUS STRESS IMPLICATIONS AND EXTENSION VELOCITY AT THE ELBOW
Three dimensional motion capture studies have yielded a relationship between greater elbow extension at peak trunk rotation and greater valgus elbow moments. Valgus elbow torque diminishes with greater elbow flexion, at the instant when peak valgus loading occurs just before MER. Combined arm lag and greater elbow extension increases the mass moment of inertia (primarily axial rotation of the humerus), which exacerbates valgus elbow stress. Peak EEV during the acceleration phase has been shown to be more associated to “arm lag” than muscular activation. This is because of centrifugal forces interacting between the trunk and humerus to assist the triceps in rapidly extending the elbow.
Contracture of the elbow flexors reveal their eccentric contribution, which has been demonstrated by an overall elbow flexor moment approximated at 40–60 Nm from the onset of acceleration. The elbow flexor moment provides joint compression and regulates EEV during the critical instant, where the elbow extends 65°, moving from 85° flexion to roughly 20° at ball release. Elbow extension deficits of 8° have been measured using passive goniometry, whereas 3° losses have been recorded post-game. Contractures are probably the result from elevated intramuscular calcium concentrations, shortening of connective tissues that encase muscle fibers, and localized inflammation. To evaluate the influence of contracture severity on pitching response, elbow extension ROMA can be used to: (a) assess eccentric effort required to decelerate elbow extension, (b) evaluate recovery status of the throwing arm, and (c) identify elbow impingement pathologies, such as osteophyte development and loose body entrapment.
Elbow extension ROMA is performed with persons lying on their side, with the acromion process and lateral epicondyle of the elbow aligned, the elbow locked at maximum extension, the thumb pointing upward (supinated wrist), and the nonevaluated arm supporting the head. Place the fulcrum of the goniometer on the lateral epicondyle of the humerus (approximating the center of the elbow joint). Align the stationary arm from the humeral lateral epicondyle to the tip of the acromion, with the moveable arm oriented along the radius to the radial styloid (Figure 9). Elbow extension deficits less than 3°, recorded immediately post-pitching and 24-hours post-pitching are considered normal. Losses greater than 10° compared with previous pitching bouts require medical attention to rule out osteophyte impingement or loose body entrapment.
To restore joint mobility, the biceps brachii should be prepped for post-game and 24-hour post-game stretching by rolling the muscle belly for 2–5 minutes using a rolling pin or another tool that provides myofascial release. As soft-tissue adhesions release and autogenic inhibitory responses are prompted, the biceps brachii will be more pliable for static stretching to further elbow extension recovery. The biceps-anterior deltoid wall stretch is a simple effective stretch, whereby the athlete abducts the arm 65° (about chest height), places the thumb into the wall, and then gently rotates the torso away from the fixed arm to stretch the anterior deltoid and biceps brachii (Figure 10).
Elbow flexor elongation combined with eccentric contraction protects the throwing athlete from valgus extension overload (VEO). VEO injuries arise because of ineffective elbow valgus torque stabilization combined with rapid elbow extension during peak throwing arm acceleration. Chronic elbow extension insufficiency impairs eccentric elbow flexor function, exacerbates VEO, and mediates posteromedial olecranon osteophyte formation, elbow impingement syndrome, and fragmentation.
Biceps curls are effective exercises to improve elbow flexion torque, but improper carrying angles mediate poor valgus stabilization and exacerbate valgus stress by prematurely fatiguing the dynamic stabilizers. External shoulder rotation combined with wrist supination during the upward (concentric) phase of the biceps curl increases valgus elbow torque (Figure 11). Valgus stress is reduced with correct technique, by internally rotating the shoulders and completing the movement with the hands at shoulder height, just inside the acromion processes (Figure 12).
Towel curls strengthen elbow flexors by eccentrically targeting different muscle synergists, according to grip orientation. With the athlete seated or standing and the elbows supported and flexed (Figure 13), begin the first repetition using a “hammer” towel grip. The strength coach instructs the individual to isometricaly activate their elbow flexors and then slowly pulls the towel down by applying an elbow extension force, for which the athlete resists. Thereafter, alternate grip positions between a supinated and pronated grip. Repeat this sequence three times for each grip for a total of nine repetitions if over the age of 15, twice for a total of six repetitions for persons under 15 years. Extension force is applied gradually and evenly throughout the entire range of motion. Communication between partners is essential to stipulate grip type, to set appropriate resistance and verbal cue to commence the routine (Figure 13a–c).
Successful strength and conditioning programs are protective and reinforce desired pitching mechanics in association to the critical instant (maximal external rotation to the follow-through). Descriptors of the exercise prescriptions and training guidelines associated to critical instant training are outlined in Table 2. The critical instant presents the greatest injury risk to the throwing arm, where prevention of extreme external shoulder rotation, reduced MER-M, enhanced MIR-M, and controlled elbow extension deceleration have the potential to mitigate greater mechanical resistance to valgus stress. By integrating the prescribed exercises, pitching efficiency may be improved by producing the highest ball velocities while attenuating upper extremity kinetics (forces and torques) and kinematics (angular velocities and accelerations) known to predispose the elbow to injury. Current injury guidelines have not addressed the importance of prescribing protective exercise or strength and conditioning regimens that are practiced in post-pitching or recovery to restore neuromuscular control of movement, inflammation, and tensile stress resistance (11).
Baseball injury research recognizes pitch accumulation and pitch type as the main proponents to pitching injuries (6,15,16). Although pitch count and type have been associated with injury, further investigation concerning physical maturity, training status, and underlying biomechanics is warranted (4,10,13).
Baseball injury statistics associated with pitch volume (pitch totals and frequency of pitching) and pitch type are misleading when relating both injury factors to pitching roles (4). Correlations between total accumulation and the frequency of curveballs thrown were not observed among relief and closing pitchers, given this cohort generally pitch at high intensity and accumulate lower pitch volumes with little variability in pitch type. Regardless of pitching roles, strength and conditioning regimens are tremendously important and must be coordinated with pitching instruction, practice, and game scheduling in maintaining health and performance. In the future, elbow injury statistics may decline with greater attention to ROMA methods, corresponding safety measures in training, eccentric strength maintenance, and inflammatory treatment within amateur, collegiate, and professional baseball pitchers.
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Keywords:© 2012 National Strength and Conditioning Association
baseball training; baseball pitching injuries; injury prevention training in baseball; throwing biomechanics