Sequenced physiologic muscle activations in the upper and lower extremity result in an integrated biomechanical task. This sequencing is known as the kinetic chain, and, in upper extremity dominant tasks, the energy development and output follows a proximal to distal sequencing. Impairment of one or more kinetic chain links can create dysfunctional biomechanical output leading to pain and/or injury. When deficits exist in the preceding links, they can negatively affect the shoulder. Rehabilitation of shoulder injuries should involve evaluation for and restoration of all kinetic chain deficits that may hinder kinetic chain function. Rehabilitation programs focused on eliminating kinetic chain deficits, and soreness should follow a proximal to distal rationale where lower extremity impairments are addressed in addition to the upper extremity impairments. A logical progression focusing on flexibility, strength, proprioception, and endurance with kinetic chain influence is recommended.
Dynamic upper extremity dominant tasks such as throwing, hitting, and serving occur as the result of the integrated, multisegmented, sequential joint motion, and muscle activation system known as the kinetic chain. Proper utilization of the kinetic chain allows maximal force to be developed in the core which can then be efficiently transferred to the arm during these actions. In order for the tasks to be effective and efficient, the kinetic chain links (the different body segments) must have optimal amounts of muscle flexibility, strength, proprioception, and endurance as well as the ability to perform the task consistently on a repetitive basis. Proper kinetic chain sequences referred to as biomechanical “nodes” have been previously described for baseball pitchers and tennis players [
The kinetic chain rehabilitation approach is not unlike other treatment philosophies in that the early or acute stage of rehabilitation is focused on protecting healing tissue and reducing pain. This is traditionally accomplished with protection (rest and/or immobilization), anti-inflammatory medication, and selected therapeutic modalities. However, these remedies are designed to treat the symptoms rather than the cause of dysfunction, therefore, a clinician must not place extraneous amounts of effort in this phase or consider these treatments as the core of the therapy program.
Following initial protection, the patient should be transitioned into what is known as the recovery phase of rehabilitation [
Following the correction of the surrounding deficits, the next step in the logical progression would be to direct the treatment efforts on stabilizing the scapula. Primary scapular stabilization and motion on the thorax involves coupling of the upper and lower fibers of the trapezius muscle with the serratus anterior and rhomboid muscles. The lower trapezius has a role as a scapular stabilizer when the arm is lowered from an elevated position by helping maintain the scapula against the thorax [
The scapular position that allows optimal muscle activation of the shoulder joint muscles to occur is that of retraction and external rotation which results from synergistic muscle activations in patterns from the hip and trunk through the scapula to the arm, which then facilitates maximal muscle activation of the muscles attached to the scapula [
At this latter point in the rehabilitation process (the functional phase), general glenohumeral strengthening would be introduced. Open chain exercises attempt to isolate the rotator cuff muscles through long lever, single plane ranges of motion which could potentially create shear across the joint creating muscular irritation. The exercises are often performed in nonfunctional positions (prone or supine) which discourages proper kinetic chain activation [
The factors contributing to dysfunction of the arm in overhead athletics can be traced to anatomical and biomechanical causes both locally and distally to the site of symptoms. Shoulder pain can result from bony pathology such as acromioclavicular or sternoclavicular injury, fractures to the clavicle or humerus, and bone spur/osteophyte formation. It can also derive from soft tissue causes such as labral injury, rotator cuff disease, or glenohumeral instability. These injured or altered structures may require surgical repair in order for rehabilitation to be successful. Pain may also occur as a result of altered mechanics/kinematics which can occur as the result of muscle weakness and/or tightness in one or more muscle groups in either the upper or lower extremity.
In the event the anatomical tissue has not been compromised, clinical focus should be on reestablishing optimal segmental activation in order to redevelop arm function. Functional tasks are dependent upon appropriate functioning of the kinetic chain as a unit, optimization of the individual components (proper flexibility and strength), and appropriate coordination of the individual segments. Each segment plays a critical role in helping an individual achieve optimal athletic performance. For example, the large muscles of the lower extremity are designed to generate power and create a firm stable base of support. This stable base allows core muscles to activate causing the trunk to have dynamic stability so the arm can direct the resultant energy in the overhead throwing motion. In the event that one or more of the segments fail to properly generate or transfer energy along the kinetic chain, the load distribution and force output become altered making the task being performed less efficient and effective. Over time, this decreased efficacy can cause otherwise healthy tissue to become irritated and stressed leading to injury.
The ideal principles for integrated functional kinetic chain rehabilitation which help assure optimal functioning of each segment are: to (1) establish proper postural alignment, (2) establish proper motion at all involved segments, (3) facilitate scapular motion via exaggeration of lower extremity/trunk movement, (4) exaggerate of scapular retraction in controlling excessive protraction, (5) utilize the closed chain exercise early, and (6) work in multiple planes.
The common proximal (in relation to the ground) causes of distal dysfunction include poor rear foot control, a lack of ankle range of motion, hip extensor and abductor tightness and/or weakness, limited spinal mobility, limited pelvic motion/strength, and poor scapular control. These unaddressed deficits lead to dysfunction along the kinetic chain resulting in poor rehabilitation outcomes.
The local and global stabilizers of the trunk together provide optimal core stability. The larger global muscles including the abdominal muscles and erector spinae, and hip abductors are vital to power generation and stability for upper extremity function. The incorporation of core strengthening into rehabilitation regimens has been shown to increase hip extensor muscle strength [
Most postural concerns can be addressed by improving the flexibility of the musculature and/or the mobility of the bony components. Flexibility of both the upper and lower extremity can be increased via standard static, dynamic, and/or ballistic stretching. Based on previous findings regarding flexibility deficits in upper extremity dominant athletes, the hamstring, hip flexor, hip adductors, hip rotator, and gastrocnemius/soleus muscle groups should be targeted for the lower extremity. Improving lower extremity muscle flexibility has been linked to improving lower body movement patterns and improving overall athletic performance [
Specifically in overhead athletes, it has been shown that acute and chronic changes in muscle due to eccentric load can affect the amount of overall shoulder motion [
Sleeper stretch.
Cross-body stretch.
Corner stretch.
Periscapular muscles such as the serratus anterior and lower trapezius should be a point of focus in early training and rehabilitation. Early training should incorporate the trunk and hip in order to facilitate proximal to distal sequencing of muscle activation. It is important to remember that scapular rotation is accessory in nature whereas scapular translation is physiologic or voluntary. Therefore, implementing exercises which attempt to isolate scapular rotation are not functional and should be discouraged. Utilizing the lower extremity in order to encourage scapular motion is ideal in that it mimics kinetic chain sequencing. Minimal stress is placed on the glenohumeral joint during hip and trunk extension which facilitate scapular retraction. All exercises are started with the feet on the ground and involve hip extension and pelvic control. The patterns of activation are both ipsilateral and contralateral. Diagonal motions involving trunk rotation around a stable leg simulate the normal pattern of throwing (Figures
(a) Facilitation of scapular retraction: hip and trunk extension facilitates scapular retraction. (b) Facilitation of scapular protraction: hip and trunk flexion facilitate scapular protraction.
Exploitation of the transverse plane helps accentuate both scapular retraction and protraction. By forcing proximal stability, the hip and trunk muscle activations, which have been demonstrated to precede arm motion, will be more effective during a specified task [
Scapular protraction is a necessary kinematic translation which occurs during the ball release through follow-through phases of the throwing motion. Protraction occurs, via serratus anterior activation, during the throwing motion as a primary mechanism in maintaining contact between the humeral head and glenoid fossa. Protraction also occurs during the deceleration phase of throwing as the arm moves forward [
The serratus anterior muscle is a multifunctional muscle designed to move and stabilize the scapula in various positions of arm elevation. One of the muscle’s more important functions is to externally rotate the scapula which occurs at terminal scapular retraction (Figures
(a) Starting position for the lawnmower maneuver. (b) This exercise accentuates scapular external rotation through the use of the transverse plane.
Excessive scapular protraction does not allow optimal rotator cuff activation to occur [
Kinetic chain-based rehabilitation activities have been grouped into open and closed chain [
The rationale behind the closed-chain framework is to maximize the ability of the inhibited muscles to activate. This involves placing the extremity in a closed-chain position, emphasizing normal activation patterns, and focusing on the muscle of interest by deemphasizing compensatory muscle activation. For example, if a patient presents with shrugging during arm elevation, then it can be assumed that the lower trapezius and/or serratus anterior are not working effectively enough during the dynamic task. A closed chain exercise such as the low row should be utilized because the short lever positioning in conjunction with the pelvis and trunk acting as the driver facilitates lower trapezius and serratus anterior coactivation which decrease the activation of the upper trapezius [
(a) Starting position for low row exercise. (b) Terminal position for low row exercise.
Strengthening and stabilization should begin by emphasizing work in successful planes and then progress to deficient planes. Clinicians should avoid the use of single planar exercises which isolate specific muscles or specific joints. Greater isolation should be utilized in the later stages of the rehabilitation protocol. During the early phases, emphasis should be placed on achieving successful positions, motions, and muscle activation sequences. In this manner, normal physiologic activations are restored, which lead to restoration of normal biomechanical motions.
Most activities, whether they are sports-related or normal daily movements, occur in the transverse plane. Therefore, the transverse plane should be exploited particularly in the early phases of rehabilitation. The protocol should progress to more unilateral planes as normal scapulohumeral kinematics are restored.
Once the kinetic chain deficits have been corrected, and normal kinematics have been restored, the focus should transition to muscle endurance and proprioception. Three areas of focus should be implemented: lower extremity muscle power and endurance, integrated sports-specific exercise, and upper extremity power and endurance. High repetition exercises designed to increase lower extremity muscle endurance should be employed first. For example, pitching is a task requiring activation of multiple segments; repetitively, adequate muscle endurance of all involved muscle groups is necessary for optimal performance. Focus on the gastrocnemius/soleus, quadriceps, hamstrings, and hip abductor muscle groups would be recommended (Figures
Side stepping.
(a) Examples of hip abduction strengthening. (b) Examples of hip extension strengthening.
(a) Power position begins with the dominant arm in the 90/90 position and forearm pronated. (b) Next, while maintaining the 90/90 arm position, rotate the trunk forward to simulate the throwing motion phases of acceleration to ball release.
(a) Starting position for the step back exercise. (b) Step back with power position encouraging use of a stable back leg.
Rebounder with power position.
General arm pain not generated by disrupted anatomy or kinetic chain deficit suggests that the extremity is being used too often or incorrectly. Excessive use or repetition without appropriate recovery time leads to muscular fatigue which in turn decreases muscular activity and force production, subsequently causing biomechanical abnormalities (decreased cocking, dropped elbow), all of which can result in pain or soreness. Adequate rest and recovery should be allotted in order for muscular function to be less affected by the stress of physical activity.
Following the alleviation of pain and soreness, restoration of the kinetic chain deficits, and improvement in strength and endurance of the necessary muscles, throwing progressions can be applied [
Rehabilitation of the throwing athlete’s shoulder should follow a kinetic chain-based regimen that addresses specific deficits within individual links which can aid in restoring the natural proximal to distal muscle activation sequencing. The deficits can be addressed through a logical progression of therapeutic interventions focusing on flexibility, strength, proprioception, and endurance with integrated kinetic chain components. Preventative or prospective exercises to minimize future loading stresses should be included at the end of rehabilitation as part of the return to function.