If truth be told, I am not a master of functional anatomy or body kinematics. Having said that, I feel it is the responsibility of any trainer or coach working with young throwing athletes to have a solid working knowledge of the shoulder. It is an unstable joint to start with and in my experiences, one of the most often injured areas with young athletes. This article will provide an overview of how the shoulder joint functions and how Proprioceptive Neuromuscular Facilitation (PNF) training can play a significant role in both injury prevention and improved performance.
Three primary joints provide motion of the shoulder
1. Glenohumeral
2. Sternoclavicular
3. Acromioclavicular
Glenohumeral Joint
The Glenohumeral Joint (GH) is a modified ball and socket joint, which consists of the humeral head (top of the upper arm bone) as well as the glenoid fossa (which is the hollow space on the lateral portion of the scapula). As I mentioned above, the intersection of these two structures creates an incredibly movable yet unstable joint. The bulk of the stability this joint has is supplied by the muscles that blanket the bony intersection and secondarily by the capulsar-ligamentous complexes including the glenoid labrum, a structure often injured in throwing athletes.
Sternoclavicular Joint
The Sternoclavicular Joint (SC) is a synovial joint (which means it is articulated in such a way so as to allow for free movement). It comprises the medial end of the clavicle, the first rib and the manubrium of the sternum. Although skeletally appearing unstable, the SC joint is quite secure due primarily to attaching ligaments.
Acromioclavicular Joint
The Acromioclavicular Joint (AC) consists of the acromial end of the clavicle along with the medial portion of the acromium of the scapula. Much like the SC joint, the AC joint draws its stability from surrounding ligaments rather than bony structure. The AC joint lacks stability however and can be easily dislocated.
The other joint providing motion of the shoulder is the Scapulothoracic Joint (ST). Although not considered a true joint (because it has no actual articulation of bones), the ST joint is in reality the most critical joint of the shoulder-arm complex. Essentially, the ST joint determines the position and therefore movement of the scapula.
The Glenohumeral Joint is capable of eight separate movements.
- Abduction
- Adduction
- Flexion
- Extension
- Internal Rotation
- External Rotation
- Horizontal Abduction
- Horizontal Adduction
Each of these movements, while occurring at the GH joint, is associated with movements at the scapula as well as each of the other shoulder joints.
Abduction
This is the upward movement of the arm in the frontal plane from anatomical position.
True abduction of the GH joint (referred to as true Glenohumeral motion) is limited to only 90 degrees. Beyond 90 degrees, it is a combined effort between both the GH and ST joints. In fact, at 180 degrees abduction (arm straight up overhead), only two-thirds of the movement occurred at the GH joint (30 degrees on its own, 90 degrees combined with the ST joint and the remaining 60 degrees exclusively occurring at the ST joint). This seamless combination of movements between the humerous and the scapula is referred to as the scapulohumeral rhythm.
During the initial phase of abduction (first 30 degrees), the motion is isolated to the GH joint as mentioned above. As the joint range exceeds 30 degrees, the ratio between scapular and humeral motion fixes at 1 degree of scapular motion for every 2 degrees of humeral motion.
Having said that, for every 15 degrees of abduction of the humerous, 10 degrees occurs at the GH joint and 5 degrees comes from the rotation of the scapula at the ST joint. The muscles largely responsible for the initial phase of abduction are the deltoid and supraspinatus.
During the subsequent phase of abduction (between 90 to 150 degrees), other muscles including the traps and serratus anterior become involved. The final phase (150 to 180 degrees) includes motion within the vertebral column, specifically amplification of the lumbar lordosis.
Adduction
This refers to returning the humerous from the abducted position to its naturally hanging position.
Adduction of the shoulder is performed by the pectoralis major along with the latissimus dorsi.
Flexion
This is the upward motion of the arm toward the front of the body.
True forward flexion at the GH joint ranges from 0 to 90 degrees, with the movement itself separated into three distinct phases. The initial phase ranges from 0 to 60 degrees and is controlled by the anterior deltoid, coracobrachialis and the pectoralis major (clavicular fibers).
During the second phase (60 to 120 degrees), scapulohumeral rhythm once again becomes important (as with abduction). The percentage of motion once more, fixes at 1 degree of scapular movement for every 2 degrees of movement at the humerous. The secondary musculatures, which assist this phase of forward flexion, are the trapezius and infraspinatus.
During the final phase of forward flexion (120 to 180 degrees), once again amplification of the lumbar lordosis becomes essential (i.e. at this end range, flexion is limited at the GH and ST joints, so movement at the spinal column becomes necessary).
From 0 to 180 degrees of motion, the humerous moves 120 degrees at the GH joint, while 60 degrees of movement occur with the scapula at the ST joint.
Extension
This is the return of the arm from the flexed or elevated position back to the anatomical position.
Hyperextension of the GH joint is the posterior motion of the humerous in the sagittal plane of the body.
Extension of the shoulder is often referred to as posterior elevation. For maximal posterior elevation to occur, internal rotation of the shoulder is required. Extension is produced by the deltoid, latissimus dorsi and teres major, with assistance coming from the teres minor as well as the long head of the triceps.
Internal (medial) Rotation
It is possible to measure the internal rotation of the GH joint in three positions:
1. With the arm at the side in normal anatomical position.
2. With the arm at 90 degrees of abduction.
3. With the arm in posterior extension (or elevation).
Internal rotation is produced by the scapularis, pectoralis major, latissimus dorsi and teres major. Range of motion is affected by tension or restrictions of the external rotators (infraspinatus and teres minor).
External (lateral) Rotation
External rotation of the GH joint is measured in two positions: 1. With the arm at the side, elbow flexed at 90 degrees and the forearm parallel to the sagittal plane of the body.
2. With the arm abducted to 90 degrees, the elbow flexed to 90 degrees and the forearm parallel to the floor.
One�s dominant hand will likely carry with it an increased range of external rotation.
External rotation is produced by the teres minor, supraspinatus and infraspinatus. As with above, range of motion is limited by the tension or restrictions of the internal rotators.
Horizontal Abduction
This is for moving the humerous laterally and backward with the humerous elevated to a horizontal position.
Horizontal abduction ranges from 0 to 30 degrees and is produced by the posterior deltoid, infraspinatus and teres minor. Motion can be restricted due to tension within the pectoralis major and anterior deltoid muscles.
Horizontal Adduction
This refers to moving the humerous medially and forward with the humerous elevated to a horizontal position.
Horizontal adduction ranges from 0 to 130 degrees and is produced by the pectoralis major and anterior deltoid. Motion can be restricted due to tension within the GH joints, extensor muscles, latissimus dorsi, teres minor, teres major and posterior deltoid.
As made obvious by the description of each of the motions possible at the GH joint, the ST joint plays an extremely crucial role in shoulder mobility and therefore safety. Having said that, I will briefly outline the motions available at the ST joint.
- Elevation
- Depression
- Abduction or Protraction
- Adduction or Retraction
Elevation
Naturally, during elevation the scapula moves upward. The trapezius, serratus anterior, as well as the levator scapulae produce this action.
Depression
Conversely, depression is the downward motion of the scapula. Passive depression of the scapula occurs due to gravity and the weight of ones arm, but simple depression is produced by the pectoralis minor and major, subclavius and latissimus dorsi muscles.
Abduction (protraction)
This is the forward movement of the scapula, which is seen in all forward pushing or thrusting movements.
This motion is produced by the serratus anterior, pectoralis minor and levator spinae.
Adduction (retraction)
This is the backward movement of the scapula and is exemplified by pulling.
This motion is produced by the trapezius and rhomboids, but is assisted to a large degree by the latissimus dorsi.
Now that I have briefly outlined the very intricate anatomy of the shoulder complex, it is crucial that we discuss the specific functional aspects of a throwing motion including defining what a throwing motion is. Are baseball, football and tennis coaches all going to read this article with the same interest? Are the parents of young pitchers going to be more interested in this article than the parents of a young quarterback or tennis star? The reality is that when discussing shoulder health, there are SEVERAL sports in which shoulder safety is a pressing concern - and yet little more than basic static stretching is the current means of maintaining the health, integrity, and functional strength of the shoulder in young athletes.v
As evidence of my point above, several studies have confirmed the notion that the throwing angle between the arm and the trunk in projecting a football, javelin, tennis racquet, or baseball are essentially the same.
What must become clear to coaches and trainers is that an increase in functional flexibility (that is flexibility based on active ability and therefore includes strength throughout the range of motion) is necessary for throwing actions. The larger the available range of motion, the longer the force-time curve and therefore the more potential force can be applied to the motion. Simply stated, larger ranges of motion allow for a larger pre-stretch of the specific muscles involved in the motion thereby permitting them to produce greater forces and increase velocity.
The following is a brief look at some of the concerns and issues facing young throwing athletes.
There is a fascination in the young population with building strong chests and shoulders often at the expense of developing the corresponding musculature on the posterior chain. This can lead to dramatic imbalances and instability.
Many coaches and trainers advocate the use of static stretching for the purpose of increasing or improving the range of motion for specific dynamic shoulder actions. For instance, statically stretching the rotator cuff internal rotators is suggested as a means of increasing shoulder external rotation and therefore the range and velocity of a throwing motion. The issues here reside in the fact that (a) isolated stretching of the rotator cuffs internal rotators does not include attention to other extremely important internal rotators such as the pectoralis major and latissimus dorsi and (b) that static forms of flexibility are of minor relevance to dynamic movement considering that functional flexibility is controlled by the nervous system and is velocity specific.
Most young athletes are instructed to perform isolated rotator cuff strengthening exercises as a means of promoting shoulder stability and increasing strength. This approach is narrow-minded at best considering that the rotator cuff is not solely responsible for either shoulder performance or health. Again, movement is controlled by the nervous system and involves synergistic force applied by several different muscles. Attempted isolation of any of those muscles makes no practical sense.
This last point requires a longer explanation.
Isolated rotator cuff exercises disregard the role that other muscles play with respect to shoulder stability and movement. The most useful exercises I have found to improve the performance of throwing athletes are ones that integrate all muscle groups responsible for shoulder motion by using functional movement patterns. These patterns strengthen the appropriate muscles through the motion in which they will be used. More over, the idea that isolation of a muscle is possible is incorrect. Mel Siff said it best: While a limb is moved, some parts of the body have to be stabilized to allow that movement.
Proprioceptive Neuromuscular Facilitation as a TRAINING tool
One of the mistakes made with respect to PNF is when it is referred to as a type of stretching. Misunderstood by most, PNF is a conditioning system, which plays on the neuromuscular processes of the body and involves diagonal movement patterns crossing the sagittal midline.
Two types of PNF training exist.
1. Classical PNF: Hands-on approach involving a therapist or other knowledgeable professional.
2. Modified PNF: Revises particular PNF techniques for use as specific exercises with external apparatus.
With classical PNF, the therapist alternates between passive and active motion through a preset direction or movement pattern. This pattern, as mentioned above, will typically follow a diagonal path and cross the sagittal midline of the body (because most muscles are oriented on an oblique angle and therefore naturally move in a diagonal manner). Classical PNF involves combining concentric, eccentric and isometric contractions in various combinations. There are several different types of PNF techniques including:
1. Repeated Contractions: This involves contracting the agonistic muscle group during a specific movement pattern. With advanced athletes, an isometric contraction can be performed at the end of a specific range until the effort of that contraction is lessened due to fatigue.
2. Slow Reversal: This involves an isotonic contraction of the antagonist and then a subsequent isotonic contraction of the agonist.
3. Slow Reversal-Hold: This involves an isotonic contraction of the antagonist and then an isometric contraction of the same. This is followed by the same sequence for the agonist.
4. Contract-Relax: This involves a maximal isotonic contraction of the antagonist against a resistance, immediately followed by a period of relaxation. Subsequently, the therapist will passively move the limb through the range of motion to a new point of restriction.
With modified PNF, specific patterns can be trained via external apparatus. When I say apparatus, I am referring to items such as pulley systems or other free motion cable devices, which do not lock the body into either false stability (i.e. sitting on a machine) or predetermined patterns of movement.
The concepts and adequate implementation associated with PNF training are highly involved. This article touched on only a few specific issues relating to PNF techniques as a means of outlining why proposed isolated shoulder exercises for throwing athletes may not be the most optimal option for shoulder safety and performance. For further reading on this subject, I highly recommend the following books:
Science of Flexibility by Michael Alter
Superstretch by Mel Siff
Facts & Fallacies of Fitness by Mel Siff