does stretching reduce injury risk?
Purpose. Researchers at the National Center for Injury Prevention and Control and the National Center for Chronic Disease Prevention and Health Promotion systematically reviewed the research literature in order to assess whether stretching effectively prevents sports injuries and to make recommendations for research and prevention.
The Methods
Thacker and colleagues searched electronic databases, including MEDLINE (1966– 2002), Current Contents (1997– 2002), the Biomedical Collection (1993–99), the Cochrane Library and SPORTDiscus; identified citations from the papers retrieved; and contacted experts in the field. The researchers limited their meta-analysis to randomized trials and cohort studies with interventions that included stretching. Studies were excluded if they lacked controls, if they did not assess stretching independently or if there were no subjects involved in sporting or fitness activities. One author initially screened all articles. Only six of the 361 articles selected compared stretching and other methods for effective injury prevention. The results shown below include data from many of the other 355 studies. One author abstracted the data, which were 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.
The Results
The following are select (not comprehensive) findings of this review:
Stretching to Improve Flexibility. Twenty-seven reports published since 1962 indicated that stretching increased trunk flexibility as well as flexibility about the knee, hip, shoulder and ankle joints. There was evidence that PNF (proprioceptive neuromuscular facilitation) was more effective for improving flexibility than other stretching methods, but this was not demonstrated consistently. The review found that 15- or 30-second passive stretches were more effective than shorter-duration stretches and as effective as stretches of longer duration. For the hamstrings, passive stretching (i.e., stretching with the help of props or another person) was shown to be more effective than dynamic stretching.
Adverse Effects of Stretching/Flexibility. There was some evidence that stretching and/or increased flexibility could have unintended adverse effects, such as temporary strength deficits and increases in arterial blood pressure. Recent studies of passive stretching showed significant adverse effects on jump performance and plantar flexion. Several studies reported that increased flexibility decreased running economy and peak performance, but these findings were not consistent.
Warming Up to Prevent Injury. With both stretching and warm-up activities (low- to moderate-intensity aerobic activity) often used prior to athletic exercise, their independent effects on injuries were difficult to assess. The review found that warming up combined with stretching increased the flexibility of the ankle, hip and knee joints. One report demonstrated that static stretching and a cycling warm-up increased flexibility equally for at least 15 minutes. One summary of 22 studies from the 1950s and 1960s found that flexibility and performance (particularly speed and strength) in a number of sporting activities improved after warm-up, especially when stretching was vigorous, sustained and related to the activity to be undertaken. Passive methods of increasing body temperature (e.g., hot baths, moist heat) also tended to increase performance, but to a lesser degree. Massage had an inconsistent effect on performance.
Risk Factors for Injury. Questionnaires and personal logs of runners and other athletes showed either no association between stretching and injury, no protective effect or no increased injury rates. Stretching after wrist hyperextension against weight decreased muscle soreness in college volunteers; in other studies, however, stretching before or after exercise had no effect on postexercise pain prevention. Studies of flexibility or joint laxity often showed no association with injury, whereas other studies found that lack of flexibility (i.e., tightness) was associated with specific injuries. One study of 303 military trainees found that the most flexible and least flexible men were at significantly increased risk of injury in a multivariate analysis.
Intervention Studies. Six controlled studies specifically addressed the role of stretching in injury prevention. Three of them focused on specific muscle groups (e.g., heel/calf, hamstrings), and three on multiple muscle groups. Two targeted the prevention of shin splints and/or tibial stress reactions. Pooled analysis of five of the studies found that stretching was not significantly associated with a reduction in the total number of injuries.
Overall Results of the 361 Studies. Stretching was not significantly associated with a reduction in total injuries (odds ratio = 0.93). Similar findings were seen in the subgroup analyses. Thacker and colleagues concluded that “there was insufficient evidence to endorse or discontinue routine stretching before or after exercise to prevent injury among competitive or recreational athletes.” The reviewers stated that further research, especially in the form of well-conducted randomized and controlled trials, was urgently needed to determine stretching’s proper role in sports.
Comments
This review is an impressive resource covering many studies on whether stretching and warming up can prevent injury. Interested readers are encouraged to read the full paper in the March 2004 issue of Medicine & Science in Sports & Exercise.
For fitness professionals, a key question arises regarding stretching and warming up. Which is more important for improving performance and reducing the risk of musculoskeletal injury? In this context the authors stated that they could neither endorse stretching nor recommend that it be discontinued. They noted several theories that might explain how stretching could compromise performance and how injury rates could be unaffected or even increased by stretching. These theories include less efficient joint movement resulting from decreased joint stability; injuries stemming from increased tissue compliance with decreased energy absorption by tendon and muscle tissue; decreased strength before the recovery phase of training; and increased pain tolerance leading to skeletal and tissue damage.
Fitness professionals should be judicious with the use, especially the excessive use, of stretching exercise. There are no hard-and-fast answers as to how much stretching and precisely which flexibility exercises are best for everyone. Such recommendations should be made conservatively and on a case-by-case basis.
