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Muscular Stretching: Facts and Fallacies

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  1. Muscular Stretching: Facts and Fallacies C. S. Nasin, MD Adapted from A. Buetler, MD Primary Care Sports Medicine

  2. Learning Objectives • Review the history and cultural importance of muscular stretching • Review the current literature on stretching • Improved flexibility • Flexibility as a risk factor • Prevention of sports injuries • Review recent hypotheses to explain the mixed EBM finding

  3. History of Stretching • 500-700 B. C.: origin of gymnastics--as it was believed that this would facilitate unity of mind and body. • 5000 B.C.: The primitive origins of martial arts

  4. History of Stretching Yoga: sanskrit ‘to unite’ A series of spiritual practices arising > 5,000 years ago. • Hatha yoga: developed in the 15th century; utilized asanas (body postures) to seek self-enlightenment • 16.5 million Americans now practice yoga, a 3 billion dollar fitness industry

  5. Athletic Culture “Stretching has become embedded in sport folklore as the universal strategy for injury prevention” -Thacker S., et al Med Sci Sports Exerc. 2004.

  6. Does stretching improve flexibility?

  7. Stretching: short and long-term changes Short term: • Redistribution of liquid and polysaccaharides within the collagen matrixes of the tendon-McNair et al. Med Sci Sports Exerc 2001 • Duration of increased flexibility 60-90 minutes–DePino et al J. Athletic Training 1982; Moller et al Arch of Phys Med Rehab 1985

  8. Stretching: short and long-term changes Long term: • Structural changes within the collagen (changes in the viscoelastic properties) - Kubo et al J. Physiology 2002 • Increased flexibility after an extensive program may last for several weeks-McCue et al Res Q 1953; Zebas et al Curr Sel Res, 1985

  9. Does flexibility decrease our risk of injury?

  10. Defining Flexibility & StretchingSafety in Middle Ground Epidemiology of Injuries Associated with Physical Training in Young Men in the Army Jones et al - Med Sci Sports Exer, 1993 • 303 Army Basic Trainees • Baseline Fitness Assessment • Questionnaire and Fitness Testing • Final Assessment • Final Army PT Test • Tracked all physician visits for 12 weeks

  11. Risk FactorOdds Ratio Flexibility Q1 (lowest 20%) 3.6* Q2 1.7 Q3 (mid 20%) 1.0 Q4 1.9 Q5 (highest 20%) 3.3* Training Unit Low Mileage 1.0 High Mileage 1.6 Risk FactorOdds Ratio Age > 24 4.3* Smoking 1.9* Previous Injury No Injury 1.0 Non-Sprain Injury 0.6 Ankle Sprain 1.7* Physical Activity Above Average 1.0 At or below Avg 2.2* Defining Flexibility & StretchingSafety in Middle Ground Risk Factors for Lower Extremity Musculoskeletal Injuries (Adjusted Ratios) * = 95% CI greater than 1.0 Epidemiology of Injuries Associated with Physical Training in Young Men in the Army – Jones et al

  12. Defining Flexibility & StretchingSafety in Middle Ground Least Flexible  Mid  Most Flexible

  13. Does stretching prevent injury?

  14. CLINICAL SCIENCES Clinical Investigations The Impact of Stretching on Sports Injury Risk: A Systematic Review of the Literature STEPHEN B. THACKER1, JULIE GILCHRIST2, DONNA F. STROUP3, and C. DEXTER KIMSEY, JR.3 1Epidemiology Program Office, 2National Center for Injury Prevention and Control, and 3National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, GA 361 Articles reviewed Included: -Only RCT or cohort studies that included stretching -Excluded: -Studies that lacked controls -Studies where stretching could not be independently assessed -Studies that did not include subjects in sporting activities Medicine & Science in Sports & Exercise 2004

  15. A prospective study on the management of shin splints.Andrish T, et alJ. Bone Joint Surg 1974 (56) 1697-1700. • 2777 male Navy midshipmen; randomized into one of five groups: • Heel pad (4.4%) • Heel stretch (4.0%) • Pad + stretch (3.0%) • Graduated run (6.0%) • Control (3.0%)

  16. High-School football injuries: effects of a post-halftime warm-up and stretching routine.Bixler B, Jones RFamily Practice Residency Journal • 5 Pennsylvania HS football teams; 128 games • 3/5 teams performed 3min half-time warm-up/stretch • No difference in total 3rd Quarter injuries; intervention group with less sprains/strains.

  17. Effects of ankle dorsiflexion range and pre-exercise calf muscle stretching on injury risk in army recruitsPope R, et alAust J Physiother 1998; 44(3): 165-172. • 1093 male army recruits in 12 platoons 12 wk basic training • Two 20s calf stretches before rigorous exercise (Intervention) • Two 20s tricep stretchs before rigorous exercise (Control) • 23 vs 25 lower extremity injuries (p=0.76)

  18. Effects of a static stretching program on the incidence of lower extremity musculotendinous strainsCross K, Worrell TJ of Athletic Training, 1999 34(1): 11-14. • 195 Div III football players; 1994/1995 seasons • 1994- no stretching • 1995- static stretching program prior to conditioning (hamstrings, gastrocs, quads, adductors) • No difference in overall injuries; significant decrease in lower ext. musculotendinous injuries (21 vs 43)

  19. Increasing hamstring flexibility decreases lower extremity overuse injuries in military basic trainees.Hartig D, Henderson JAm. J. Sports Med 1999 (27) • 298 Army recruits @ Fort Benning; 2 basic trainee companies • Intervention group: TID static hamstring stretches • Results: • Intervention: 25 LE overuse injuries (17%) • Control: 43 LE overuse injuries (29%)

  20. A randomized trial of pre-exericse stretching for prevention of lower-limb injuryPope R, et alMed & Sci in Sport & Exerc. 2000 (32) • 1543 male australian army recruits from 39 training platoons • Intervention: 20s supervised stretches of 6 major LE muscle groups before each training exercise • Results: • Intervention: 158 LE injuries (21%) • Control: 175 LE injuries (22%)

  21. Meta-Analysis Results: Stretching and Primary Prevention of Athletic injuries Thacker et al (MSSE 2004) • Review of 361 articles; 6 included • No association • Herbert & Gabriel (BMJ 2002) • 5 studies included • No association between stretching and injury or muscle soreness. • Yeung & Yeung (Cochrane Review 2001) • Review of 118 articles; 12 included • No association

  22. Difficulties in Stretch Studies • Timing of stretching • Type of stretching • Intrinsic RF for injuries • Extrinsic RF for injuries • Gender • Differences between sports/positions “I pity the fool who does this research”

  23. Stretch-Shortening Cycles (SSC)and Muscle Tendon Unit Compliance: Another Piece of the Puzzle Stretch-Shortening cycles (SSC):is a natural muscle function where a concentric action is preceded by an eccentric action, and this leads to a higher concentric torque value in healthy persons. -High SSC Sports (i.e. bouncing and jumping activities): soccer, football, rugby -Low SSC Sports: jogging, swimming, cycling Stretching and Injury Prevention: An Obscure Relationship -Witvrouw E, Mahieu N, Danneels L, and McNair P Sports Medicine 2004 34 (7): 443-449.

  24. High SSC Sports: Requires storage and release of elastic energy High Compliance tendon: more energy can be absorbed by the tendon tissue, reducing trauma to muscle. Increased energy Absorption Decreased Work

  25. Low SSC Sports: benefit with low compliance tendon for efficient energy transfer Low Compliant tendon: forces will be transferred to the contractile apparatus and little will be absorbed by the tendon Decreased energy Absorption Increased Work

  26. The effect of sports specific training on reducing the incidence of hamstring injuries in professional Australian Rules Football players.Verrall GM - Br J Sports Med - 01-JUN-2005; 39(6): 363-8 • Single ARF team followed • Intervention group: Hamstring stretches with muscle fatigue; sports specific drills, and ↑high intensity aerobic cross-training • Significant reduction in Hamstring strains & missed games (p=<0.05)

  27. A survey of flexibility training protocols and hamstring strains in professional football clubs in England.- Dadebo B - Br J Sports Med - 01-AUG-2004; 38(4): 388-94 • Questionnaire data from 30 professional English teams collected 1998/99 • Stretching was the most important training factor assoc. with HSRs (not statistically significant)

  28. Incidence, risk, and prevention of hamstring muscle injuries in professional rugby union.- Brooks JH - Am J Sports Med - 01-AUG-2006; 34(8): 1297-306 • Nordic hamstring strengthening and HS stretching regimens decreased rates and severity of HSRs.

  29. So what are the answers? • Stretching DOES increase flexibility • Flexibility IS a risk factor for injury at the extremes • “There is not sufficient evidence to endorse or discontinue routine stretching before or after exercise to prevent injury among competitive or recreational athletes.”-Thacker et al 2004 • May be of particular importance in high SSC sports

  30. Questions??