The Impact of Stretching on Sports Injury Risk: A Systematic Review of the Literature'

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The Impact of Stretching on Sports Injury Risk A
Systematic Review of the Literature.

• THACKER, S. B., J. GILCHRIST, D. F. STROUP, and
  C. D. KIMSEY, JR. The Impact of Stretching on
  Sports Injury Risk A Systematic Review of the
  Literature. Med. Sci. Sports Exerc., Vol. 36, No.
  3, pp. 371-378, 2004.

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Introduction Types of Stretches

• Static stretching
• Static stretching prevents muscle spindles from
  shortening the muscle
• Passive stretching

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Introduction Types of Stretches

• Ballistic stretching
• May activate muscle spindles which produce muscle
  shortening

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Introduction Types of Stretches

• Proprioceptive Neuromuscular Facilitation
• Contract muscle to stimulate GTO
• GTO cause muscle to relax
• Stretch relaxed muscle further

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Introduction Measuring Flexibility

• Static Flexibility
• Goniometer joint angles
• Fleximeter degree of bending
• Arthrometer measure joints
• Relationship between static flexibility to
  dynamic flexibility?

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Introduction Flexibility and Injuries

• Little evidence of link between flexibility and
  injury rate
• Imbalance in flexibility may increase injury risk
• Stretching may increase performance or it may
  decrease performance

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Purposes

• Review of the literature
• Evidence that stretching prevents injury
• Effect of warm-up on injury prevention
• Recommendations

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Methods

• Searched electronic data bases, including MEDLINE
  (1966-2002), Current Contents (1997-2002),
  Biomedical Collection (1993-1999), the Cochrane
  Library, and SPORTDiscus
• Meta-analysis was limited to randomized trials or
  cohort studies for interventions that included
  stretching.
• Six of 361 articles compared stretching with
  other methods to prevent injury.
• Data were abstracted by one author and then
  reviewed independently by three others. Data
  quality was assessed independently by three
  authors using a previously standardized
  instrument, and reviewers met to reconcile
  substantive differences in interpretation. We
  calculated weighted pooled odds ratios based on
  an intention-to-treat analysis as well as
  subgroup analyses by quality score and study
  design.

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Results Stretching-Flexibility

• Stretching increases joint flexibility
• PNF stretching may be more effective
• 15-30 second stretch is more effective than
  shorter stretches.
• Passive is more effective than dynamic.
• Flexibility gains last 6-90 minutes

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Results Adverse Effects

• Stretching has been linked to strength deficit
  and increased blood pressure
• Adverse but inconsistent effects on jump
  performance, running economy and peak
  performance.
• Increased flexibility may enhance performance

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Results Warm-up

• Warm-up with stretching increases flexibility,
  has no effect on muscle soreness, and prevents
  injuries.
• Warm-up improves flexibility and performance.
• Passive warming is less effective
• Massage shows inconsistent results
• Excessive warm-up may lead to early fatigue

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Results Risk Factors for Injury

• Questionnaires show no association between
  stretching and injury prevention.
• Evidence that high and low degrees of flexibility
  increase the risk for injury.

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Results Intervention Studies

• Stretching is not associated with a reduction
  injuries.

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Discussion

• Stretching increases flexibility.
• Extremes of flexibility can increase risk for
  injury.
• Normal flexibility and injury prevention not
  supported by research findings.
• The relevance of static flexibility to dynamic
  performance is uncertain.

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Discussion

• Flexibility seems to be sport/event specific as
  well as joint specific.
• Stretching might not prevent injuries but may
  impair performance.
• Decrease joint stability
• Dangerous body positions stretching of ligaments
• Decrease strength
• Increase pain tolerance
• Little, if any effect, on damage from eccentric
  contractions

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Discussion

• Randomized controlled studies show no protective
  effect from stretching.
• Not enough evidence to eliminate stretching.
• No studies on at risk populations.
• Warm-up and conditioning may be more effective.

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Discussion

• Based on this review, we can recommend neither
  the endorsement nor the discontinuation of
  stretching,...
• The evidence demonstrates that stretching
  clearly increases flexibility and, to the degree
  that flexibility might benefit performance or
  decrease the risk of injury, stretching might be
  desirable.
• It is also evident that strength training,
  conditioning, and warm-up have an important role
  in injury prevention
• We suggest that when stretching is done, it
  should be conducted in the context of adequate
  conditioning and appropriate warm-up.

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Discussion

• Future studies
• Well-conditioned competitive athletes, variety of
  sports, and both genders and various age groups.
• Well-conditioned recreational athletes
  particularly those with poor flexibility.
• Methodological issues

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Conclusion

• There is not sufficient evidence to endorse or
  discontinue routine stretching before or after
  exercise to prevent injury among competitive or
  recreational athletes.
• Further research, especially well-conducted
  randomized controlled trials, is urgently needed
  to determine the proper role of stretching in
  sports.