Dynamic stability of the throwing shoulder requires fine, coordinated action of the GH and scapulothoracic stabilizers to facilitate synchronous function of the GH joint. After surgery, proper neuromuscular control must be reestablished to prevent asynchronous muscle-firing patterns, which can result in dysfunction.1,2

Neuromuscular control is defined as a purposeful act initiated at the cortical level.³ Payton, Hirt, and Newton³ stated that motor control is an involuntary associated movement organized subcortically that results in a well-learned skill operating without conscious guidance. The fine coordinated activity necessary for propelling a ball rapidly and accurately requires subcortical control of the muscles responsible for throwing.

Kinesthesia is the ability to discriminate joint position, relative weight of body parts, and joint movement, including speed, direction, and amplitude.⁴ Proprioception is the ability to discriminate joint position.

The ability to throw requires that joint proprioceptors (muscle and joint afferents present in ligament and synovial tissues) function normally. Joint proprioceptors within the GH joint are responsible for signaling a stretch reflex when the GH capsule is taut to prevent translation at extremes of motion.⁵ Many throwers recovering from surgery, especially those who have undergone procedures for instability, complain of stiffness and tightness in their shoulders. Neuromuscular controls may have been arrested by trauma and surgery, resulting in a new subcortical sense of joint tightness during throwing that was not present before the shoulder-stabilization procedure.

The upper extremity (UE) and shoulder represent the last link in the kinetic chain during the overhead-throwing motion, which begins distally as ground reactive forces are transferred caudally. Biomechanical analysis shows that tremendous forces are generated and extreme motion occurs in the shoulder with overhand throwing. Angular velocities in excess of 7000°/sec have been recorded during the transition from external rotation to internal rotation when throwing.^6,7 Shearing forces on the anterior shoulder are estimated at 400 N.⁶ Approximately 500N of distraction force occurs during the deceleration phase of the throwing motion.⁶ These forces are short in duration, develop quickly, occur at extremely high intensity, and must be performed repeatedly. The direction and magnitude of the forces generated when throwing a ball cause anteroposterior translational and distraction vectors that stress the GH constraints.

However, these forces are not entirely generated in the shoulder. The shoulder-supporting musculature is not capable of generating the forces and motions measured at the shoulder during throwing. Throwing a ball effectively requires the athlete to generate, summate, transfer, and regulate these forces from the legs through the throwing hand. To generate the forces measured with throwing, the shoulder relies on its position at the end of the kinetic chain. It has been reported that 51% to 55% of the kinetic energy created is generated in the lower extremities (LEs).^8,9 Use of ground reaction forces sequentially linked with the activity of the large LE and trunk muscles generate a significant proportion of the forces measured. Biomechanical data show that the shoulder itself contributes relatively little of the overall total energy necessary to the throwing motion. However, it provides a relatively high contribution to the total forces (21%), indicating that the shoulder, because of its position at the end of the kinetic chain, must effectively transfer and concentrate the developed energy. Conditioning of the shoulder and UE musculature is important in returning throwing athletes back to their sports. Moreover, the trunk and LE musculature must be adequately conditioned to provide the foundation to generate the forces required for effective and safe throwing.

When designing a program to return a throwing athlete back to sports, the physical therapist (PT) should consider two primary objectives: (1) enhancing current performance levels and (2) preventing injury. Gambetta¹⁰ has outlined ten key principles that are basic to the development of a conditioning program for the throwing athlete (Box 13-1). The many components of the program must work together to produce optimal performance. The quality of the effort and the overall intensity should be emphasized first. The clinician should monitor each exercise and eventually scrutinize the throwing technique to ensure the optimal training effect and minimize the potential for injury.

The development of muscle balance is essential for coordinated, efficient movement to occur, especially around the shoulder where muscle imbalance can easily develop. Muscles (e.g., the rotator cuff) cannot simply be trained solely and in isolation, as in the early phases of most postoperative programs. After base strength has been developed in the postoperative shoulder, functional activities and more sport-specific exercises must be added to mimic the activities the athlete will be performing.

The development of core strength in the abdominals, trunk, and spinal-stabilizing muscles cannot be overemphasized. Without adequate core strength, the throwing athlete becomes vulnerable to improper postural alignment, which can lead to compensatory movements that place even greater stress on the shoulder, further predisposing the athlete to injury. After adequate strength has been achieved in the shoulder-supporting musculature, abdominals, spinal stabilizers, and LEs, endurance training can be added.

Only after sufficient strength and endurance have been developed and normal, synchronous muscle-firing patterns have been reestablished can a more functional and sport-specific activity such as throwing be added. The ultimate success of the training program depends on its overall design in introducing a variety of training stimuli to maximize total conditioning. An ideal conditioning program should contain a preparation period, an adaptation period, and an application period.¹⁰ The preparation period should consist of general work, including strength and endurance training. Specialized work incorporating joint dynamics of the sport occurs during the adaptation period. Finally, the application period incorporates the specific joint actions and movements required to perform the sport.

Weight training is one of the most popular methods of training and can be performed with either free weights or machines. Free weight training with dumbbells is preferable, because it allows for unilateral training while permitting a full range of motion (ROM) of the extremity. Machines are better used in training the LEs. The use of rubber tubing or bands is another popular method of early strength training for the overhand-throwing athlete. These exercises can be performed as a warm-up for more strenuous weight resistance exercises or as a cool down exercise; they can accommodate all muscle actions. Rubber tubing or band exercises also allow for unilateral training of the extremity through a full ROM. They can be performed during the rehabilitation period and should continue when the thrower returns to play. Isotonic strengthening can be tailored to each athlete’s needs and can be used to maintain strength in all muscle groups. Jobe’s UE exercise program11 is the most popular group of isotonic exercises performed. They can be initiated early in the rehabilitation period and continued throughout the athlete’s career. However, they must be performed correctly to maximize their benefit (Table 13-1).

Core strength should first be developed using isotonic training. Only after base strength is developed should the intensity of the exercise program be increased (Table 13-2).

Plyometric training was first introduced in the late 1960s by Soviet jump coach Yuri Verkhoshanski.12 American track coach Fred Wilt¹³ first introduced plyometrics in the United States in 1975. The majority of the literature concerning plyometric exercise discusses its use in the LEs. Adapting these principles to the conditioning of throwing athletes is logical, considering the maximal explosive concentric contractions and rapid decelerative eccentric contractions that occur with each throwing cycle. Although agreement regarding the benefits of plyometric exercise in the training program is well documented, controversy exists regarding its optimal use.^14–17

Plyometric exercise can be broken down into three phases: (1) the eccentric (or setting) phase, (2) the amortization phase, and (3) the concentric response phase. The setting phase of the exercise is the preloading period; it lasts until the stretch stimulus is initiated. The amortization phase of the exercise is the time that occurs between the eccentric contraction and the initiation of the concentric contraction. During the concentric phase the effect of the exercise (a facilitated contraction) is produced and preparation for the second repetition occurs.

Clinicians believe physiologic muscle performance is enhanced by plyometric exercise in several ways. The faster a muscle is loaded eccentrically, the greater the resultant concentric force produced. Eccentric loading of a muscle places stress on the elastic components, increasing the tension of the resultant force produced.

Neuromuscular coordination is improved through explosive plyometric training. Plyometric exercise may improve neural efficiency, thereby increasing neuromuscular performance.

Finally, the inhibitory effect of the Golgi tendon organs, which serve as a protective mechanism limiting the amount of force produced within muscle, can be desensitized by plyometric exercise, thereby raising the level of inhibition. This desensitization and the resultant raise in the inhibition level ultimately allow increased force production with greater applied loads.

Through neural adaptation, the throwing athlete can coordinate the activity of muscle groups and produce greater net force output (in the absence of morphologic change within the muscles themselves). The faster the athlete is able to switch from eccentric or yielding work to concentric overcoming work, the more powerful the resultant response. Effective plyometric training requires that the amortization phase of the exercise be quick, limiting the amount of energy wasted as heat. The rate of stretch rather than the length of stretch provides a greater stimulus for an enhanced training effect. With slower stretch cycles the stretch reflex is not activated.

Before implementing a plyometric training program, the patient must have an adequate level of base strength to maximize the training effect and prevent injury. Remedial shoulder exercises focusing on the rotator cuff and shoulder-supporting musculature are continued in order to develop and maintain joint stability and muscle strength in the arm decelerators. These exercises also should be used to warm up before the plyometric drill and cool down after it has been concluded.

Plyometric exercise is contraindicated in the immediate postoperative period, in the presence of acute inflammation or pain, in athletes with gross shoulder or elbow instability, or in both. Plyometric training also is contraindicated in athletes who do not have an adequate degree of base strength and who are not participating in a strength-training program. This form of exercise is intended to be an advanced form of strength training. Postexercise muscle soreness and delayed-onset muscle soreness are common adverse reactions that the clinician should be aware of before beginning an athlete on this type of exercise.

Tremendous amounts of stress occur during plyometric exercises; therefore they should not be performed for an extended period. A plyometric program should be used during the first and second preparation phases of training.

The plyometric training program for the UE can be divided into four groups of exercise as described by Wilk¹⁸ (Table 13-3):

Warm-up exercises are performed to provide the shoulder, arms, trunk, and LEs an adequate physiologic warm-up before beginning more intense plyometric exercise. The facilitation of muscular performance through an active warm-up has been ascribed to increased blood flow, oxygen use, nervous system transmission, muscle and core temperature, and speed of contraction.^4,19–22 The athlete should perform two to three sets of 10 repetitions for each warm-up exercise before proceeding to the next group of exercises.

Throwing movement plyometric exercises attempt to isolate and train the muscles required to throw effectively. Movement patterns are performed similar to those found with overhead throwing. These exercises provide an advanced strengthening technique at a higher exercise level than that of more traditional isotonic dumbbell exercises. The exercises in this group are performed for two to four sets of six to eight repetitions two to three times weekly. Adequate rest times should occur between each session for optimal muscle recovery.

Plyometric exercises for trunk strengthening include medicine ball exercises for the abdominals and trunk extensor musculature. The athlete performs two to four sets of 8 to 10 repetitions two to three times weekly.