Swimming Biomechanics: Injury Prevention and Treatment.
Jason Gauvin, PT, SCS, ATC, CSCS
James N. Johnson, MD
Michael Fredericson, MD
BackgroundSummer “splashers” account for a large portion of the 100-120 million Americans who enjoy recreational swimming (1,2), with a significant number of coached, competitive swimmers. USA Swimming has recently surpassed 250,000 registered swimmers of pre-school through college age, and United States Masters Swimming has over 38,000 members age 19 to 100+. High school and summer league swimming participation is roughly estimated at 5 million over and above the USA Swimming membership (3-6).
Competitive swimmers train 10,000-20,000 yards/meters per day, using the freestyle arm stroke for most of the distance. At an average of 8-10 arm cycles per 25 yards, a swimmer completes over one million shoulder rotations each week (6). Swimmers are obvious at risk for “overuse” injuries, especially to the shoulder.
With new biomechanical developments and new instruction techniques, shoulder injury incidence may be on the decline but remains a common problem. Sports medicine professionals can implement new prevention strategies and coaching techniques by understanding the biomechanics and pathomechanics of the freestyle stroke. By using prevention and rehabilitation strategies for shoulder impingement, sports medicine professionals may prevent the progression of the initial injury into a rotator cuff tear, worsening capsular laxity, or glenoid labral tear.
Common Injuries
Shoulder impingement and overuse injuries are still common because of the number of strokes each swimmer performs in a given week. Cole et al. (7) studied shoulder injuries in 325 swimmers during the 1996-97 swimming season and reported an occurrence rate of 30% of all injuries that year. Bak et al (8) also reported a 38% incidence of shoulder injuries per year in swimmers. Furthermore, McMaster and Troup (9) reported a lifetime shoulder injury incidence of 47-73% for competitive swimmers whereas Pink et al. (2) reported a 47% lifetime incidence in collegiate swimmers and 48% in master’s swimmers (10). The more recent literature suggests injury rates are declining, which may result from improved understanding and knowledge regarding biomechanics, injury prevention, treatment, and the application of new coaching techniques.
“New” Biomechanics
Much has been written regarding swimming biomechanics and shoulder injury prevention, but new theories and coaching techniques have developed in the last decade. Counsilman’s (11) two-dimensional biomechanical analysis in 1971 showed that freestyle swimming propulsion was primarily due to lift forces based on Bernoulli’s principle of Hydrodynamic Forces. From these data, the description of an S-shaped pull was developed (12). However, in 1994, Rushall et al (13) disproved this theory with a computer-generated, three-dimensional biomechanical model. They found that freestyle propulsion was primarily attributable to drag forces based on Newton’s Third Law of Motion. The presumed S-shaped stroke developed in the two-dimensional model failed to consider body rotation. The Rushall analysis accounted for body roll and developed the concept of the “straight-through” pull that caused coaches to rethink their paradigm of the freestyle arm stroke. The buzzwords in coaching became “body rotation, balance, and core strength.”(14) Additional studies in 2001 by Riewald (15) supported the early catch, straight-through pull, early exit freestyle technique, which emphasizes equal body rotation (45° each direction) and balance in the water and exercise training of core strength.
Freestyle Biomechanics and Muscle Activity Souza (16) describes the freestyle stroke accurately as an early pull-through (catch), late pull-through, and recovery (exit), more simply explained in the swimming community as catch, pull, and recovery. Pink et al. (2) studied the normal freestyle arm-stroke with fine-needle EMG. The normal “catch” at forward hand entry into the water occurs as the upper trapezius elevates and the rhomboids retract the scapula. The serratus anterior protracts and upwardly rotates the scapula and is highly active from this point in the catch and through the pull. The scapula is held in place by these opposing, force-coupling actions. Just after the catch the pectoralis major fires and adducts and extends the humerus with some component of internal rotation balanced and coupled with the antagonistic external rotation of the teres minor. The latissimus dorsi fires from the mid pull-through until the beginning of recovery in concert with the subscapularis. The deltoid and supraspinatus are the prime movers through recovery (2).
Freestyle Pathomechanics
The etiology of the painful shoulder in swimmers can be attributed to a myriad of stroke flaws. A hand entry, which crosses the midline of the long-axis, causes a mechanical impingement in the anterior shoulder at the long head of the biceps and the supraspinatus (figure 1). This is exacerbated by a thumb first entry, which further stresses the biceps attachment to the anterior labrum. A crossover pull-through usually results from a crossover entry (figure 2) and increases the duration in the impingement position. Proper body roll, however, can resolve most of the impingement risks provided the athlete does not have glenohumeral instability/anterior capsular and concomitant anterior subluxation.
Asymmetric body roll or unilateral breathing may increase impingement by causing a compensatory crossover pull-through on the side with less roll or on the non-breathing side. Improper head position, forward sloping shoulders, and scapular instabilities are also implicated in arm, shoulder, upper back and neck pain that may or may not be associated with neurologic signs and symptoms (16).
Injury Prevention and Rehabilitation
Prevention of injury requires a team approach and a thorough understanding of the swimming principles, biomechanics and the appropriate exercises that produce the muscle “BALANCE” or force coupling necessary for remaining injury free. The freestyle swimmer must maintain muscular balance between the upper and lower trapezius and rhomboids, which is counterbalanced by the serratus anterior for scapular stabilization. Also, the lower trapezius and serratus anterior should be counterbalanced by the upper trapezius and the rhomboids for acromion elevation. Other important opposing muscles are the subscapularis vs. the infraspinatus/ teres minor and the deltoid vs. the posterior rotator cuff muscles. The activation of the rotator cuff provides a dynamic stabilization to the shoulder directly through muscular control and indirectly through dynamic ligament (i.e., capsular) tensioning.
The scapula must be stabilized by the 17 muscles that attach to it for the shoulder joint to be strong and stable yet sufficiently mobility required for function, a principle commonly referred to as proximal stability for distal mobility. Muscular balance allows for rhythmical scapular motion to occur and assists in keeping the shoulder joint injury-free. Unfortunately, the muscular balance can become “unbalanced” and dyskinesis or asymmetrical scapular movement may occur. Scapular dyskinesis should be addressed with a full evaluation and treated with an appropriately prescribed stretching and strengthening exercise program. A standard strengthening program for a swimmer should consist of isolated movements, combined movements, and endurance training exercises. Isolated exercises should focus on the serratus anterior, rotator cuff and middle and lower trapezius.
EMG analysis by Pink et al. (2) in swimmers with painful shoulders reveals the most prominent abnormality as a weakness of the serratus anterior and increased activity of the rhomboids during the pull. Other opposing muscle changes include decreased subscapularis and increased infraspinatus activity during recovery. The resulting mechanical imbalance/“floating scapula” increases anterior impingement of the biceps and supraspinatus tendons (2). Glousman et al. (17) reported that the lower trapezius and serratus anterior muscles are most susceptible and sensitive to muscular weakening or inhibition. Scovazzo (18) found that swimmers with painful shoulders had serratus anterior muscles that became less active or inactive, causing the rhomboids to substitute for the weakened serratus anterior. Fifteen to 20 percent of a muscle maximum voluntary contraction is the highest level at which sustained activity can be performed without fatigue (18). Pink et al. (2) reported that the serratus anterior and subscapularis continually fire at more than 20 percent of their maximum; therefore, these two muscles appear to be susceptible to fatigue. If this is true, prevention of overuse injury may be possible with aggressive strengthening and endurance training of the serratus anterior, lower trapezius, and possibly the subscapularis, including the rotator cuff. Pink et al’s (2) EMG studies and resulting therapy recommendations for scapular stabilization are now widely accepted and utilized in the rehabilitation of shoulder injuries.
Kibler (19) maintains that shoulder injury is prevented first by core stabilization followed by scapular stabilization. He describes the scapula as the link in the kinetic chain from the legs and trunk to the shoulder. Sports medicine professionals are now recognizing the importance of strengthening the entire kinetic chain for the prevention and treatment of most injuries, specifically shoulder injuries.
Moseley et al. (20) found that 12 exercises qualified as “top exercises” for the 8-scapular/shoulder muscles tested. They reported that 4 exercises that should make up the core scapular muscle strengthening program should include scaption (Figure 3), push-up with a plus (Figure 4 & 4a), rowing (Figure 5) and press-ups (Figure 6). Townsend et al. (21) found four different exercises consistently challenged the muscles they tested. These exercises were elevation in the scapular plane with IR (empty can), flexion, horizontal abduction with ER, and the press-up. More recently, Decker et al. (22) presented the “dynamic hug” as an alternative serratus anterior “isolation” exercise. It has also been suggested to endurance train the serratus anterior by using an upper body ergometer or arm bike and encouraging exaggerated protraction with this exercise (2). Others have suggested a focus on the lower trapezius, which can be emphasized in humeral extension with humeral ER and retraction of the scapula (16). The supraspinatus can be emphasized in scaption with humeral IR or ER with peak EMG activity noted between 90-120 degrees of elevation. Internal rotation and external rotation should be performed in a continuum of positions from 0 degrees of abduction to the scapular plane to 90 degrees of abduction (20-24). It is believed that this will challenge the shoulder’s dynamic stabilizers and enhance muscular strength and endurance. Exercise sets should utilize more than the standard 3-4 sets of 10 repetitions. Sets to fatigue or 10 sets of 10 repetitions may be more appropriate to train these relatively small stabilizing and endurance muscles
Commonly, swimmers lack IR and horizontal adduction (across the chest) range of motion. These impairments must be treated with isolated stretching or mobilization techniques to those muscle or positions causing the ROM restrictions. Sports medicine professionals must determine the origin of the ROM restriction (i.e. capsular or muscular tightness). Stretching of the pectoralis major and minor, posterior shoulder (posterior capsule and/or posterior rotator cuff muscles), and latissimus dorsi can assist in managing the symptoms associated with shoulder impingement.
Core strength provides the final link in the prevention and treatment plan. Lower abdominal strength should be emphasized in the dry land conditioning program for swimmers. The goal of abdominal strengthening is to develop increased control of the pelvis in a neutral position. Core strength and endurance provides proximal stability for distal mobility and can result in more energy efficient swimming technique and possibly improved performance. Flawless swimming technique requires excellent trunk control and muscular balance in the scapulohumeral/ scapulothoracic joints.
Conclusions
Shoulder pain is the most common complaint in swimmers. Understanding the freestyle stroke and common injury patterns may help identify any underlying biomechanical or training-related cause of injury. In addition, a better understanding and quick tips on stroke technique and instruction in a proper strengthening and stretching exercise programs may help prevent new injuries or prevent recurrence in a patient with chronic shoulder problems. With the “new” freestyle techniques that emphasize body rotation and balance, scapular stabilization, appropriate stretching, and core strengthening can be an important part of injury-free swimming and, ultimately, more effective technique and performance.
REFERENCES
1. Murphy T: Shoulder injuries in swimming, in Andrews JR, Wilk KE: The Athlete’s Shoulder. New York City, Churchill Livingstone, 1994, p 411
2. Pink M, Jobe F: Biomechanics of swimming, in Zachazewski JE, Magee DJ, Quillen WS: Athletic Injuries and Rehabilitation. Philadelphia, Saunders, 1996, p 317
3. USA Swimming Web site: http://www.usa-swimming.org/. Accessed October 25, 2002
4. United States Masters Swimming Web site: http://www.usms.org/. Accessed October 25, 2002
5. National Collegiate Athletic Association Web site: http://www.ncaa.org/ Accessed October 25, 2002
6. Kammer CS, Young CC, Niedfeldt MW: Swimming injuries and illnesses. Phys Sportsmed 1999;27(4):51-60
7. Cole A, Johnson JN, Fredericson M: Injury incidence in competitive swimmers. Presented at USA Sports Medicine Society and American Swim Coaches Association meeting; September 7, 2002; Las Vegas, NV
8. Bak K, Bue P, Olsson G: Injury patterns in Danish competitive swimming. Ugeskr Laeger 1989;151(45):2982-2984
9. McMaster WC, Troup J: A survey of interfering shoulder pain in United States competitive swimmers. Am J Sports Med 1993;21(1):67-70
10. Stocker D, Pink M, Jobe FW: Comparison of shoulder injury in collegiate- and master’s-level swimmers. Clin J Sport Med 1995;5(1):4-8
11. Counsilman, JE: Competitive Swimming Manual for Coaches and Swimmers. Bloomington, Indiana, Cousilman Co. Inc, 1977
12. Maglischo EW: Swimming Even Faster. Mountain View, CA, Mayfield Publishing Company, 1993
13. Rushall BS, Sprigings EJ, Holt LE, et al: A reevaluation of forces in swimming. J Swimming Research 1994;10(fall):6-30
14. Boomer B, Nelms M: The Boomer Chronicles [Videotape Series]. Colorado Springs, CO: USA Swimming; 2000
15. Riewald S: Biomechanical forces in swimmers. Presented at USA Sports Medicine Society; April 15, 2002; Colorado Springs
16. Souza TA: The shoulder in swimming, in Sports Injuries of the Shoulder: Conservative Management. New York City, Churchill Livingstone, 1994, pp 107-24
17. Glousman R, Jobe F, Tibone J, et al: Dynamic electromyographic analysis of the throwing shoulder with glenohumeral instability. J Bone Joint Surg. 1988 70A:220-226.
18. Scovazzo ML, Browne A, Pink M, et al: The painful shoulder during freestyle swimming: an electromyographic and cinematographic analysis of twelve muscles. Am J Sports Med 1991;19(6):577-582
19. Kibler WB: The role of the scapula in athletic shoulder function. Am J Sports Med 1998;26(2):325-337
20. Moseley JB Jr, Jobe FW, Pink M, et al: EMG analysis of the scapular muscles during a shoulder rehabilitation program. Am J Sports Med 1992;20(2):128-134
21. Townsend H, Jobe F, Pink M, Perry J: Electromyographic analysis of the glenohumeral muscles during a baseball rehabilitation program. Am J Sports Med 1991:19(3): 264-272
22. Decker MJ, Hintermeister RA, Faber K,
Hawkins, RJ. 1999. Serratus Anterior muscle activity during selected
rehabilitation exercises. AJSM 27(6):784-791
23. Wilk KE, Arrigo C: Current concepts in the rehabilitation of the athletic shoulder. J Orthop Sports Phys Ther 1993;18(1):365-378
24. Allegrucci M, Whitney S, Irrgang J: Clinical Implications of Secondary Impingement of the Shoulder in Freestyle Swimmers. JOSPT 1994:20(6):307-318.
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