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."
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.