Muscular Stretching: Facts and Fallacies

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Muscular Stretching Facts and Fallacies

• C. S. Nasin, MD
• Adapted from A. Buetler, MD
• Primary Care Sports Medicine

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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

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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

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History of Stretching

• Yoga sanskrit to unite
• A series of spiritual practices arising gt 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

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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.

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Does stretching improve flexibility?
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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

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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

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Does flexibility decrease our risk of injury?
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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

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Defining Flexibility StretchingSafety in
Middle Ground
Risk Factors for Lower Extremity Musculoskeletal
Injuries (Adjusted Ratios)
95 CI greater than 1.0

• Risk Factor Odds 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 Factor Odds Ratio
• Age gt 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

• Epidemiology of Injuries Associated with Physical
  Training in Young Men in the Army Jones et al

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Defining Flexibility StretchingSafety in
Middle Ground
Least Flexible ? Mid ? Most Flexible
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Does stretching prevent injury?
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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
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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)

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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.

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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 (p0.76)

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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)

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Increasing hamstring flexibility decreases lower
extremity overuse injuries in military basic
trainees.Hartig D, Henderson JAm. J. Sports Med
1999 (27)

• 298 Army recruits _at_ 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)

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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)

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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

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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
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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.
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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
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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
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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 (plt0.05)

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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)

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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.

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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

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Questions??