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Stretching the truth

[This article originally appeared in the July 2000 issue of Northwest Runner magazine.]

Is stretching good for athletes? Even among scientists, the answer you get depends on whom you ask. The American College of Sports Medicine's position stand on "The Recommended Quantity and Quality of Exercise" argues that stretching is effective in enhancing muscle performance and in preventing and treating injuries (Medicine and Science in Sports and Exercise 30: 975-91, 1998). However, two other recent review articles claim that stretching does not help athletes perform better or avoid injury (Gleim & McHugh, Sports Medicine 24: 289-99, 1997; Shrier, Clinical Journal of Sports Medicine 9: 221-7, 1999).

In the following column, I'd like to share my own take on this controversial issue. As usual, my approach is research-based rather than anecdotal; I have examined a number of scientific studies in an attempt to determine what benefits, if any, stretching confers upon its practitioners. While I don't expect everyone to agree with my conclusions, I hope that the information presented here will help readers make informed decisions about whether and how to incorporate stretching into their training routines.

Better performance?

The first key question one must ask is, "Does stretching lead to improved muscle performance?" Several research reports are commonly mentioned in support of the notion that stretching helps muscles work better; unfortunately, these are almost invariably of poor quality or irrelevant to runners or both. For example, in support of its pro-stretching stance, the ACSM cites three performance-related studies. One (Bosco et al., International Journal of Sports Medicine 3: 137-40, 1982) concerns the proper stance with which to begin a vertical jump and really has nothing to do with the style of stretching practiced by endurance athletes. A second (Worrell et al., Journal of Orthopedics and Sports Physical Therapy 20: 154-60, 1994) suggests that regular stretching improves hamstring power in initially inflexible subjects; however, this study lacked a control group and failed to achieve a statistically significant improvement in subject flexibility even though that (improving flexibility) was the point of the stretching protocol. The third (Wilson et al., Medicine and Science in Sports and Exercise 24: 116-23, 1992) demonstrated an improvement in maximal rebound bench press performance among male weightlifters who underwent an eight-week upper-body flexibility training program, a credible finding which is nonetheless of limited applicability to distance running.

An additional study not cited by the ACSM is that of Handel et al. (European Journal of Applied Physiology 76: 400-8, 1997), who found that 16 trained athletes were able to exert more force at the knee joint after an eight-week stretching program. However, this investigation employed a type of stretching known as "contract-relax" stretching which entails repeated forceful contractions of the targeted muscles; this served as a form of strength training which may have improved muscle performance independent of stretching and flexibility issues. (In support of this idea, the athletes' thighs got bigger over the course of the study.)

Thus, considered collectively, the evidence that stretching will help runners run faster is less than overwhelming, to say the least. Moreover, it is opposed by studies of running economy (Gleim et al., Journal of Orthopaedic Research 8: 814-23, 1990; Craib et al., Medicine and Science in Sports and Exercise 28: 737-43, 1996) which show that inflexible runners use less energy (i.e., are more economical) than flexible runners in covering a given distance at a given speed. The reasons for this are not clear, although the authors speculate that stiff runners may store and recycle more elastic energy from one stride to the next and/or may devote less energy to maintaining a stable upright posture while running. In any case, these intriguing papers suggest that, for endurance athletes, the use of stretching exercises to improve one's flexibility may not be such a hot idea after all.

Injury avoidance?

A second, equally important question to ask of stretching is, "Does it help prevent injuries?" Again, flexibility fans can cite articles to back their position; again, however, these studies leave much to be desired. The ACSM position paper cites six references in support of the statement that "General stretching programs have been shown to be effective in reducing both the severity and frequency of injuries"; however, only one of the six contains empirical data on the effects of stretching per se. In that investigation (Hilyer et al., Journal of Occupational Medicine 32: 631-7, 1990) -- a study of 469 municipal firefighters -- those who stretched regularly suffered the same number of on-the-job injuries and incurred the same medical costs as those who did not. The stretching group missed less work due to injury, perhaps because of its improved flexibility; however, the researchers acknowledged that this result could also be attributed to "a Hawthorne effect, peer pressure, or beliefs held by injured persons in the experimental group that the flexibility intervention had protected them from serious, long-term injury."

Regrettably, studies of running injuries (Jacobs & Berson, American Journal of Sports Medicine 14: 151-5, 1986; Walter et al., Archives of Internal Medicine 149: 2561-4, 1989; van Mechelen et al., American Journal of Sports Medicine 21: 711-9, 1993) have failed to separate the influence of stretching from potentially confounding factors such as mileage, training intensity, and so forth. Still, it is noteworthy that none of these investigators found a positive relationship between stretching habits and protection from injury.

Perhaps the largest-ever study of stretching and its injury-preventing potential was published this past winter. Pope et al. (Medicine and Science in Sports and Exercise 32: 271-7, 2000) examined 1538 Australian army recruits randomly divided into stretch and control groups. The authors summarize their results as follows: "A typical preexercise stretching protocol does not produce a clinically useful reduction in injury risk. Our best estimate of the effect of stretching is that is reduces all-injury risk by 5%, and we are able to rule out a 23% or greater reduction in injury risk with 95% certainty." They continue, "When these results are expressed in absolute terms, the futility of stretching becomes apparent. Recruits stretched for 40 sessions over the course of training, and so, on average, each recruit would need to stretch for 3100 physical training sessions to prevent one injury. As it took 5 min to complete the stretches, an average of 260 hours of stretching would be required to prevent one injury."

Caveats and conclusions

The above discussion omits several caveats which should be kept in mind. First, the importance of flexibility (and thus stretching) varies considerably from sport to sport; what may suffice for distance runners may not be adequate for gymnasts, for instance. Second, all athletic endeavors require a certain range of motion around one's joints, and athletes who can't comfortably achieve this range can certainly benefit from flexibility training. Third, certain athletes with specific problems (such as muscle imbalances, chronic tightness, or recent injury) are likely to benefit from stretching even if others do not. And fourth, stretching may yield long-term health benefits which are not apparent in the short-term time scale (weeks to months) of most exercise-related research.

Despite these caveats, though, the fact remains that there is little experimental evidence that stretching benefits the average (or above-average) distance runner. Some might advocate stretching anyway because it "can't hurt," and I don't necessarily disagree with this outlook. Nevertheless, when training time is limited, one should spend that time on the things that matter most. For many of us, stretching may be more of a luxury than a necessity, and it should therefore be prioritized as such.

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