Apr 30, 2011

Swimming Mechanics & Spinal Injuries Article

As a result of my injury in Tampa Bay, I thought I would share some research brought to my attention on swimming mechanics related to neck and spinal injuries.

I have selectively edited this rather long article for the high points, be warned it is very detailed and for none swimmers, well boring. But for those OW swimmers I think you will find this invaluable. 

Here are some close up pictures from Tampa showing the affects of wave action on my body position, arm recovery. as you can see the influences of wave movement force very different stroke patterns and technique in Open Water.

Here my rotation is about correct (although I always have arms swinging high), good catch of water out front.

Here is a good example of over rotating the body and I likely was allowing my right arm to reach too far across the mid line of my body. this puts enormous stress on the shoulder muscles.
Here is a good example of a wave (albeit small) whacking me just as a breath was being taken. As you can see to compensate, I over rotated, my legs are splitting apart to counter balance the affect. My head is also higher in the water. These actions put significant stress on the neck and spine complex.

Spinal Musculoskeletal Injuries Associated with Swimming: A Discussion of Technique

Henry Pollard BSc, GradDipChiro, GradDipAppSc, MSportSc, PhD. * Matt Fernandez BSportSc, MChiro. †
Abstract Objectives: To review the biomechanics of the swimming stroke and examine common injuries which occur in swimming. A review of diagnosis and management strategies of these injuries is also performed.

Most injuries and complaints encountered in swimming athletes occur because of repetitive microtrauma or overuse, with many injuries originating from faulty technique and poor swimming biomechanics. As a result, assessment of an injured athlete requires the practitioner to have an understanding of the four swimming strokes and hydrodynamics.

The shoulder, neck and back are the injuries considered in this review. These regions are considered in the total training program of the athlete to identify other factors, such as weight training or other dry land programs that may be contributing to injury. However, whilst rest or reduced training may be necessary for recovery, every effort must be made to keep the swimmer “in the water” as cessation of training may lead to a rapid detraining effect and loss of competitive advantage. Swimming is unique in that it provides upper and lower body strength and cardiovascular training, which is performed in a non-weight bearing environment. However the highly repetitive motion of swimming may predispose overuse injury 2-5. To fully understand the mechanisms leading a swimmer to injury, a thorough knowledge of anatomy and stroke mechanics is essential2. Additionally, knowledge on the types of drag (water resistance) and its affect on swimmers are important and will be discussed. Swimmers are subjected to the repetitive strain of many tissues of the spine and upper limb and as a result require positioning themselves in unusual anatomical positions to maximize force production. Poor flexibility of swimming stroke hampers the adaptation of such positions and may predispose to injury. 

Spinal Musculoskeletal Injuries Associated with Swimming
intricacies of the stroke mechanics, the demands placed on the muscular system and how they can impact on normal joint functioning can help the practitioner form an accurate diagnosis of injury. By utilizing knowledge of biomechanics, the practitioner can appropriately select and implement effective treatment and management strategies to address common and uncommon pain presentations.

Strokes and Hydrodynamics
The biomechanics of each swimming stroke are similar except for breaststroke, which is unique in both the upper and lower extremity motion. The remaining strokes consist of freestyle, butterfly and backstroke. These strokes can be divided into two main phases, the pull (or propulsive) and recovery phases. The pull phase provides movement with the use of two large muscles, the pectoralis major and latissimus dorsi. These act to move the arm through adduction and internal rotation starting from a stretched position of abduction/external rotation. The recovery phase allows the return of the arm to the stretched starting position while the opposite arm completes its pull phase. Efficient recovery is based on the participation of the external rotators and body roll6.

To appreciate swimming mechanics, a basic understanding of hydrodynamics and related biomechanical issues is needed. Drag is the term commonly used when referring to water resistance. There are three types of drag relevant to the swimmer: form, wave and friction drag. Form drag is water resistance that is dependent on body positioning. The more horizontal the body is positioned in the water, the less form drag. Wave drag is the turbulence at the water surface created by the moving swimmer. Wave drag can rebound from the sides or the bottom of the pool. Frictional drag originates from the contact of the skin and hair with the water. The controversy surrounding the early use of the swimming bodysuit highlighted the role of the suit in minimising frictional drag and the potential unfair advantage that could be acquired through its use. Whilst initially considered unfair, the suit is now acceptable to use in competition. The drag force is also used for propulsion during the pull pattern and the kick.

The path of the hand in the swim stroke is not linear. As a swimmer’s hand moves through the water, energy is given to the water and the water moves. The swimmer essentially pushes off “still water” which allows swimmers to generate more force. One of the main reasons swimmers use the “S” shaped pulling pattern is to continually find still water that is not moving to propel themselves forward7. These propulsive movements of the arm can be further divided into outsweep, downsweep, insweep and pull phases (see figure 1). The outsweep is the first movement in the underwater stroke for butterfly and breaststroke swimmers. The downsweep performs the same function for freestyle and backstroke. Neither of the sweeps are propulsive, but rather, they serve the arm to catch water before applying a propulsive force. The insweep is the first propulsive movement in freestyle and butterfly while it is the only propulsive movement in breaststroke. The push phase is the propulsive motion in freestyle and butterfly. 

It is clear from the above description, that during the swimming motion a great deal of emphasis is placed on the nearly global motion of the glenohumeral joint (shoulder). The greater the flexibility of this joint, the better the swimmer is able to generate power through the entire pull-through phase. Unfortunately the same flexibility may predispose the swimmer to shoulder joint instability8.  (This is my problem). The kick pattern most commonly used is the two-beat and six beat flutter kick. The two beat flutter kick has one down beat and one up beat of each leg during one stroke cycle. The six beat flutter kick has three down beats and three up beats during once arm cycle7.

Muscular Demands. 
Today, the availability of computerised, technological advances in sport science, allows for the analysis of critical information than can lead to improved swimming performance7. A discussion of the freestyle stroke follows, as it is often used as a training substitute for the other three strokes6. Freestyle muscle activity has been measured both in and out of the water. This has clinical ramifications with regards to rehabilitation, since air provides less resistance than water, thus the pull phase is less stressful6. The freestyle stroke depends mainly on the upper extremity for forward propulsion. The adductors and internal rotators largely dominate the pull phase, with force being provided initially by the pectoralis major clavicular portion followed by the latissimus dorsi. Assistance is provided by the serratus anterior and the internal rotator functions of the subscapularis and teres major6.

Efficient recovery is based on the participation of the external rotators and body roll. Recovery is a small muscle dependant movement with the rhomboid and middle trapezius retracting the scapula as the posterior deltoid, teres minor and infraspinatus externally rotate the shoulder. Shoulder abduction is performed by the middle deltoid and is assisted by the supraspinatus. The main role of the supraspinatus is to stabilize the humeral head in the glenoid thereby allowing the rotator cuff to act efficiently off the base of support created by the scapula stabilizers6. In mid recovery for hand entry preparation, the serratus anterior and upper trapezius rotate the scapula upward for shoulder stabilization. During swimming the serratus anterior has been demonstrated to function at 75 percent of its maximum test ability. Due to the repetitive nature of swimming, the lack of sufficient rest phase will inevitably lead to some fatiguing of the serratus anterior6.

Body roll cannot be underestimated during swimming. During each freestyle stroke, the upper body will roll through nearly 160 degrees7. This roll of the torso produces large forces that pull the hand and arm through the water and is a result of the large paraspinal muscles of the back and the abdominal musculature7. Perhaps the greatest difference between elite and novice swimmers is the lack of body roll and therefore power in the latter. The efficient use of the body roll helps to decrease the form drag associated swimming as the cross sectional area of the body pushing through the water is decreased with its efficient use.

The kick component for freestyle, butterfly and backstroke is performed by the repetitive movements of hip flexion and extension, knee flexion and extension, ankle plantar and dorsi flexion. The power of the thigh and calf muscles, through the kicking action are purposely timed to enhance and provide power to body roll and therefore, pull-through power7. Lumbar spine mobility during the kick is also important. In contrast the breaststroke kick begins with hip and knee flexion. The knee then extends and abducts and brings the ankles together at full knee extension. At the termination of the kick the ankles are plantar flexed.

The high reliance upon the shoulder adductors and internal rotators for forward propulsion results in excessive activity and development of the anterior chest and internal rotator muscles. Ultimately this creates internal and external musculature imbalance, thus creating the potential for anterior translation during period of co-contraction and hence, the characteristic posture noted in swimmers6. Electrical activity measured in 25 breaststroke swimmers showed an increase in activity of the internal rotators muscles in swimmers with painful shoulders. There was decreased activity in the teres minor, supraspinatus and upper trapezius muscles. These factors increased the risk of impingement10. The muscles that performed the greatest work in the normal shoulder are the muscles most likely to fatigue, they being the serratus anterior and teres minor. If left unattended, it could potentially encourage the forward translation of the humeral head causing a relative position of impingement10.

Swimmers have a tendency to be selectively hypermobile in the shoulder with the exception of a tight posterior capsule2. When the posterior capsule is tight, the hypermobile joint may cause a functional anterior translation of the humerus. During the swimming stroke application of force to the palm, the hand propeller, results in a vector thrust at the shoulder in an anterior direction, thereby exacerbating anterior shear8.

The sustained maximal ability to propel the body through the water may lead to dysfunction of the scapulothoracic muscles, as seen by winging of the scapula9. The scapulothoracic muscles are responsible for positioning the scapula and therefore the glenoid11. This results in less concavity compression needed by the rotator cuff. The dysfunctional change in the stabilisation of the scapulothoracic articulation allows forward rotation of the shoulder, exacerbating any anterior instability. Endurance based swimming workouts may not only fatigue the scapula- positioning muscles but also the rotator cuff muscles11.

Another cause of shoulder pain is a tear in the glenoid labrum12. The labrum is a fibrous structure joined to the glenoid fossa. Its major function is to deepen the concavity of the glenoid fossa, act as the origin for the glenohumeral ligaments and has a role in resisting anterior translation of the humeral head. Tears in the labrum can result from repetitive overhead movements and rotator cuff fatigue that causes forward translation of the humeral head via the mechanism previously described. In the presence of instability, a loss of attachment of the inferior glenohumeral ligament (off the anterior-inferior glenoid rim) can occur. These changes result in clicking, catching or locking of the shoulder. The pain from a labrum injury tends to be maximal midway through the pull phase of the stroke12.

Cervical Spine
The neck and its related structures often cause radiating pain to the shoulder joint8. Younger age groups are less likely to be subjected to cervical spine degenerative disease. However in the older swimmer, disc dysfunction and spondylosis could impinge on nerve roots, particularly those at C4, C5 and C6 levels, resulting in radiating pain to the shoulder joint and beyond. The athlete subjected to herniation of a cervical nucleus pulpous at C5 to C6 or may present with pain, numbness and not uncommonly, weakness in the large motor groups surrounding the shoulder girdle. Such a deficit would make swimming difficult due to the additional load placed on the neck. This would be especially true of the butterfly stroke.

The neck is also subjected to sustained and repetitive movements, which can have implications for overuse injury. 55% of total cervical movement (especially rotation) is provided by the atlanto-axial joint (C1-C2), 5% by the occiput-atlas joint (C0-C1) and the remaining 40% is spread between C2-C64. A study by Guth found that there was a greater mean range of cervical rotation in 14-17 year old swimmers than non-swimmers. In this study, the analysis was made using goniometric measurement of cervical rotation. This result supported the concept that active motion through sporting activity will contribute to a greater degree of flexibility22.

Neck over-rotation loads cervical spine ligaments and muscles, which encourages asymmetrical development. The face emerges from the water into an air pocket at the bottom of the bow wave, which is created by the head pushing through the water in the same manner as a boat. Due to the protection of the bow wave, swimmers only need minimal rotation of the head to obtain a breath22. Poor body rotation results in over-rotation of the neck in order to breathe. If the body is well rotated along its long axis then there is no requirement for the neck to over-rotate. Contributing to this error can be the practice of breathing unilaterally. Breathing only to the favoured side leads to muscular imbalances within the neck, particularly in rotation. Such muscular imbalance may be aggravated by forward head carriage, as the axis of rotation changes resulting in greater body and cervical sidebend and extension to compensate for lost rotation range of motion20. Conversely, breathing to the “bad” side may not rotate the body enough potentially contributing to over-rotation of the neck. Thus, bilateral breathing should be encouraged when possible.

Lumbo Pelvic Complex
Low back injuries in swimmers most often are caused by repetitive stress during turns and the strain of poor head and body position in the water2. Torsional strain can occur when the body does not roll as a whole unit during the stroke causing abnormal loading at the point in the spine where the rolling stops2. This predisposes the swimmer to overuse or acute injury or both. Pelvic musculature, particularly tight hip.

Spinal Musculoskeletal Injuries Associated with Swimming
flexors can reduce hip extension resulting in hyperextension of the lumbar spine and anterior pelvic tilt17. In addition, anterior pelvic tilting results in the pelvis assuming a lower than normal position in the water, creating increased drag19. Disc degeneration may occur in the older swimmer18. While this isn’t thought to be caused by swimming, it may be aggravated by certain body positions held during various individual strokes.

The hyperextension motion of the lumbar spine seen with butterfly and breaststroke can predispose to facet joint irritation, otherwise known as “Butterfly back syndrome”18. The power and range of the kick depends largely on lumbosacral mobility, as well as the flexibility of the hip, knee and ankle joints. Butterfly requires repeated flexion and extension of the trunk. The extension is necessary to elevate the shoulders to obtain clear water for the head in the recovery phase of the stroke. The “Butterfly back syndrome” is made worse if the pelvis is tilted anteriorly as this position will cause facet joint compression. If this compression becomes repetitive and chronic, it may progress to low grade joint inflammation, leading to reflexive spasm of the back muscles and pain can occur19. With continued repetitive stress, low back problems like stress fractures of the pars interarticularis (spondylolisthesis) can occur.

The management of swimming injuries must include prevention based education and activity. Effort should be made to develop a team approach by talking to the swimmer’s coach, their support staff and to other practitioners. Such an approach is important in light of the fact that most injuries occur in training and are overuse in nature. Knowledge of swimming biomechanics and the demands placed on the spinal musculoskeletal system should aid the practitioner in the diagnosis and management of injuries as well as gaining the trust of the athlete and coach. Most swimming injuries are minor and can be treated with conservative care. 

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