Does stretching prevent injury?

NewsBot · Apr 7, 2006

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Back in 2004 an attempt was made to answer this question:
The impact of stretching on sports injury risk: a systematic review of the literature.
Med Sci Sports Exerc. 2004 Mar;36(3):371-8.

PURPOSE: We conducted a systematic review to assess the evidence for the effectiveness of stretching as a tool to prevent injuries in sports and to make recommendations for research and prevention.

METHODS: Without language limitations, we searched electronic data bases, including MEDLINE (1966-2002), Current Contents (1997-2002), Biomedical Collection (1993-1999), the Cochrane Library, and SPORTDiscus, and then identified citations from papers retrieved and contacted experts in the field. Meta-analysis was limited to randomized trials or cohort studies for interventions that included stretching. Studies were excluded that lacked controls, in which stretching could not be assessed independently, or where studies did not include subjects in sporting or fitness activities. All articles were screened initially by one author. Six of 361 identified 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.

RESULTS: Stretching was not significantly associated with a reduction in total injuries (OR = 0.93, CI 0.78-1.11) and similar findings were seen in the subgroup analyses.

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.
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A subsequent meta-analysis from a similar result:
Effect of stretching on sport injury risk: a review.
Clin J Sport Med. 2005 Mar;15(2):113.

OBJECTIVE: Effect of Stretching on Sport Injury Risk: a Review To assess the evidence for the effectiveness of stretching for the prevention of injuries in sports.

DATA SOURCES: MEDLINE (1966 to September, 2002), Current Contents, Biomedical Collection, Dissertation Abstracts, the Cochrane Library, and SPORTDiscus were searched for articles in all languages using terms including stretching, flexibility, injury, epidemiology, and injury prevention. Reference lists were searched and experts contacted for further relevant studies.

STUDY SELECTION: Criteria for inclusion were randomized trials or cohort studies of interventions that included stretching compared with other interventions, with participants who were engaged in sporting or fitness activities. One author identified 361 articles reporting on flexibility, methods and effects of stretching, risk factors for injury, and injury prevention, of which 6 articles fulfilled the inclusion criteria for meta-analysis.

DATA EXTRACTION: Three independent reviewers blinded to the authors and institutions of the investigations assessed the methodologic quality of the studies (100-point scale) and reached consensus on disagreements. Details of study participants, interventions, and outcomes were extracted. Weighted pooled odds ratios were calculated for effects of interventions on an intention-to-treat basis.

MAIN RESULTS: Reduction in total injuries (shin splints, tibial stress reaction, sprains/strains, and lower-extremity and -limb injuries) with either stretching of specific leg-muscle groups or multiple muscle groups was not found in 5 controlled studies (odds ratio [OR] 0.93; 95% CI, 0.78 to 1.11). Reduction in injuries was not significantly greater for stretching of specific muscles (OR, 0.80; CI, 0.54-1.14) or multiple muscle groups (OR, 0.96; CI, 0.71-1.28). Combining the 3 ratings of methodologic quality, median scores were 29 to 60/100. After adjustment for confounders, low quality studies did not show a greater reduction in injuries with stretching (OR, 0.88; CI, 0.67-1.15) compared with high quality studies (OR, 0.97; CI, 0.77-1.22). Stretching to improve flexibility, adverse effects of stretching, and effects of warm up were not assessed by appropriate intervention studies.

CONCLUSION: Limited evidence showed stretching had no effect in reducing injuries.
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And now we have this adding to the body of knowledge from the American Physiological Society Conference:
Stretching Increases Resistance To Injury, Unless Nitric Oxide Isn't Produced

If you're a mouse, then stretching before you exercise is a good thing - even as long as two weeks before your next cheese hunt or cat run. But if you're reading this for yourself, it's a bit more complicated.

When most of us think of stretching, we're imagining at a minimum jogging, and probably something more like downhill skiing or sprints. But when University of Michigan researchers Nicole Lockhart and Susan Brooks talk stretching, their real interest is how to condition older folks' muscles so they'll eventually be willing to do even a little exercise to garner all the benefits that will follow.

"The elderly are far more susceptible to contraction-induced injury," notes Lockhart, lead author in two related papers being presented in American Physiological Society sessions at Experimental Biology in San Francisco. "Sometimes just by normal activity or a sudden movement a leg will jut out too far and they'll suffer a minor injury, but they'll be wary of further damage," she said.

Protect those muscles, as minor injuries may be cumulative

Brooks, her adviser, added: "We think that cumulative muscle injury may contribute to the loss of muscle mass as we grow old. So protecting muscles at all times is a good thing. And understanding how stretching increases resistance to injury will really help to do this."

The team had previously shown that stretching decreased muscle injury in mice when stretches were performed anywhere from one hour to 14 days (yes days) prior to exercise. But they didn't know why. What is known is that while stretching muscles produce nitric oxide (NO), a common signaling molecule. NO increases blood flow and decreases force during submaximal contractions, and also can modulate inflammation.

NO protects without stretching; but without NO, stretching doesn't seem to protect

So they tested whether the anti-inflammatory effects of NO were involved in the protection provided by stretching. And the results were: mixed. Mice were given substances that either increased or inhibited NO production. They found that increasing NO reduced inflammation and other measures of injury following exercise by half - even without prior stretching. On the other hand, when NO production was restricted, stretching an hour before exercise didn't reduce injury at all.

They also tested whether low level inflammation seen after stretching somehow primes muscles to decrease inflammation following subsequent damaging exercise. They found that when an antibody was administered that reduced the inflammation induced by stretching, no protection following subsequent exercise was observed.

Insights, but not yet answers on mechanisms of protection

"The results are somewhat contradictory," Brooks offers, "because first nitric oxide appeared to be important by inhibiting inflammation, but our second experiment showed that if you prevent inflammation you don't get the protection afforded by stretching. Nevertheless, while translating animal studies to human athletes, or elderly humans for that matter, is difficult, these studies do provide important insights into how different modes of training reduce muscle injury."
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From Medical News Today

NewsBot · Oct 4, 2007

Chronic static stretching improves exercise performance.Kokkonen J, Nelson AG, Eldredge C, Winchester JB.
Med Sci Sports Exerc. 2007 Oct;39(10):1825-31.

PURPOSE:: This study investigated the influence of static stretching exercises on specific exercise performances.

METHODS:: Thirty-eight volunteers participated in this study. The stretching group (STR) consisted of 8 males and 11 females whose activity was limited to a 10-wk, 40-min, 3-d.wk static stretching routine designed to stretch all the major muscle groups in the lower extremity. The control group (CON) consisted of 8 males and 11 females who did not participate in any kind of regular exercise routine during the study. Each subject was measured before and after for flexibility, power (20-m sprint, standing long jump, vertical jump), strength (knee flexion and knee extension one-repetition maximum (1RM)), and strength endurance (number of repetitions at 60% of 1RM for both knee flexion and knee extension).

RESULTS:: STR had significant average improvements (P < 0.05) for flexibility (18.1%), standing long jump (2.3%), vertical jump (6.7%), 20-m sprint (1.3%), knee flexion 1RM (15.3%), knee extension 1RM (32.4%), knee flexion endurance (30.4%) and knee extension endurance (28.5%). The control group showed no improvement.

CONCLUSION:: This study suggests that chronic static stretching exercises by themselves can improve specific exercise performances. It is possible that persons who are unable to participate in traditional strength training activities may be able to experience gains through stretching, which would allow them to transition into a more traditional exercise regimen.
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NewsBot · Jan 25, 2008

Temporary tendon strengthening by preconditioning
Atsushi Teramotoab, Zong-Ping Luoc
Clinical Biomechanics (Article in Press)

Background
Tendon is frequently injured structure in sports activities. Stretching before activities has been recommended to prevent athletes from injuries. Clinical studies reported that stretching had effects to reduce passive muscle stiffness and leads to an increased range of motion. Recent biomechanical studies suggested that stretching might also temporary affect tensile property of tendon. However, the detailed information regarding optimizing this preconditioning has not been defined. The purpose of this study is to investigate time-dependent effect of preconditioning on the mechanical strength of tendon, and to determine an optimal duration of preconditioning for tendon strengthening.

Methods
Forty eight Achilles tendons from euthanized Sprague–Dawley rats were used. The specimens were randomly divided into six groups. The specimens in control group were tested to failure without preconditioning. In preconditioning groups, 30, 100, 300, 600, and 1000s stretching at 2% strain were performed. The specimens were subsequently loaded to failure.

Findings
Preconditioning from 30s to 600s significantly increased the ultimate failure load and strength. Ultimate failure load was significantly different between control and each of 30, 100, 300, and 600s stretching groups (P=0.033, 0.031, 0.004, and 0.029, respectively). There was no significant difference between control and 1000s stretching group. Ultimate strength was significantly different between control and each of 30, 100, 300, and 600s stretching groups (P=0.007, 0.008, <0.001, and 0.006, respectively), but not between control and 1000s stretching group.

Interpretation
The time-dependent effect of preconditioning on the mechanical strength of tendon may be due to progressive collagen fibre recruitment and subsequent fatigues at the micro-level.
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Fiona Hawke · Jan 25, 2008

Herbert RD, de Noronha M. Stretching to prevent or reduce muscle soreness after exercise. Cochrane Database of Systematic Reviews 2007, Issue 4. Art. No.: CD004577. DOI: 10.1002/14651858.CD004577.pub2

Background
Many people stretch before or after (or both) engaging in athletic activity. Usually the purpose is to reduce risk of injury, reduce soreness after exercise, or enhance athletic performance.

Objectives
The aim of this review was to determine effects of stretching before or after exercise on the development of post-exercise muscle soreness.

Search strategy
We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register (to April 2006), the Cochrane Central Register of Controlled Trials (The Cochrane Library 2006, Issue 2), MEDLINE (1966 to May 2006), EMBASE (1988 to May 2006), CINAHL (1982 to May 2006), SPORTDiscus (1949 to May 2006), PEDro (to May 2006) and reference lists of articles.

Selection criteria
Eligible studies were randomised or quasi-randomised studies of any pre-or post-exercise stretching technique designed to prevent or treat delayed-onset muscle soreness (DOMS), provided the stretching was conducted soon before or soon after exercise. To be eligible studies must have assessed muscle soreness or tenderness.

Data collection and analysis
Methodological quality of the studies was assessed using the Cochrane Bone, Joint and Muscle Trauma Group's methodological quality assessment tool. Estimates of effects of stretching were converted to a common 100-point scale. Outcomes were pooled in a fixed-effect meta-analysis.

Main results
Of the 10 included studies, nine were carried out in laboratory settings using standardised exercise protocols and one involved post-exercise stretching in footballers. All participants were young healthy adults. Three studies examined the effects of stretching before exercise and seven studies investigated the effects of stretching after exercise. Two studies, both of stretching after exercise, involved repeated stretching sessions at intervals of greater than two hours. The duration of stretching applied in a single session ranged from 40 to 600 seconds.

All studies were small (between 10 and 30 participants received the stretch condition) and of questionable quality.

The effects of stretching reported in individual studies were very small and there was a high degree of consistency of results across studies. The pooled estimate showed that pre-exercise stretching reduced soreness one day after exercise by, on average, 0.5 points on a 100-point scale (95% CI -11.3 to 10.3; 3 studies). Post-exercise stretching reduced soreness one day after exercise by, on average, 1.0 points on a 100-point scale (95% CI -6.9 to 4.8; 4 studies). Similar effects were evident between half a day and three days after exercise.

Authors' conclusions
The evidence derived from mainly laboratory-based studies of stretching indicate that muscle stretching does not reduce delayed-onset muscle soreness in young healthy adults.

Full text available at http://mrw.interscience.wiley.com/cochrane/clsysrev/articles/CD004577/frame.html for Australia, Denmark, England, Finland, Ireland, Latin and Central America and Carribbean, New Zealand, Norway, Poland, Scotland, Spain, South Africa, Sweden, Wales, the Canadian Province of New Brunswick, the Canadian Northwest Territories, Nunavut and Yukon, the Canadian Province of Saskatchewa and the US State of Wyoming.

NewsBot · May 11, 2023

Potential Effects of Dynamic Stretching on Injury Incidence of Athletes: A Narrative Review of Risk Factors
David G. Behm, Shahab Alizadeh, Abdolhamid Daneshjoo & Andreas Konrad
Sports Medicine (2023)

The use of dynamic stretching as a replacement for static stretching in the warm-up is widespread based on the reports of static stretching-induced performance impairments. While acute and chronic static stretching has been reported to reduce musculotendinous injuries, especially with explosive and change of direction actions, the influence of dynamic stretching on injury incidence lacks a similar volume of literature for acute and chronic responses. It was the objective of this narrative review to examine the acute and training effects of dynamic stretching on injury incidence and possible moderating variables such as dynamic stretching effects on range of motion, strength, balance, proprioception, muscle morphology, and psycho-physiological responses. One study demonstrated no significant difference regarding injury incidence when comparing a dynamic stretching-only group versus a combined dynamic stretching plus static stretching group. The only other study examined functional dynamic stretching training with injured dancers and reported improved ankle joint stability. However, several studies have shown that dynamic activity with some dynamic stretching exercises within a warm-up consistently demonstrates positive effects on injury incidence. Regarding moderating variables, while there is evidence that an acute bout of dynamic stretching can enhance range of motion, the acute and training effects of dynamic stretching on strength, balance, proprioception, and musculotendinous stiffness/compliance are less clear. The acute effects of dynamic stretching on thixotropic effects and psycho-physiological responses could be beneficial for injury reduction. However, the overall conflicting studies and a lack of substantial literature compared with SS effects points to a need for more extensive studies in this area.
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Fiona Hawke Member

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