How does stretching before the big race affect my performance?
The scene just before the start of any big 10K race is always the same: thousands of runners balancing on one leg while grasping the other ankle, or straining to reach their toes. It's a perfect example of the wide gulf between sports science and common practice.
For years, researchers have been finding that the more flexible you are, the less efficiently you run - a message that tradition-bound runners have been reluctant to hear. Now, research to be published later this year in The Journal of Strength and Conditioning Research makes it clear that some (but not all) prerun stretching makes you slower.
The amount of energy you burn to run at a given pace is called your "running economy," a concept similar to fuel economy in cars. Tests of subjects, ranging from world-class British middle-distance runners to undergraduate volunteers at Nebraska Wesleyan University, have found that the better you do on a sit-and-reach test - sitting on the ground and reaching as far as possible toward your toes - the worse your running economy is.
This effect likely stems from the remarkable ability of your muscles and tendons to store energy like coiled springs, providing an estimated 40 to 50 per cent of the energy you use for each step.
"If you decrease the stiffness of the muscles and tendons, then you can't store and reutilize energy as well," explains Jacob Wilson, an exercise physiologist at Florida State University.
The connection is less pronounced in women, who are generally more flexible. And the initial studies only measured correlations, rather than showing that increasing your flexibility actually causes lower running economy.
To address this gap, Mr. Wilson and his colleagues asked 10 male runners to complete a pair of one-hour tests consisting of 30 minutes running at a predetermined pace to measure running economy, followed by 30 minutes as fast as possible. Before one of the tests, the subjects did 16 minutes of "static" stretching - the most common technique, which involves stretching a muscle to the edge of its range of motion then holding for 30 seconds.
Sure enough, the non-stretchers burned about 5 per cent fewer calories in the first part of the run, and ran 3.4 per cent farther in the second part. Though it's already well-established that static stretching causes a temporary decrease in strength and power, it's the first time the effect has been observed in an endurance activity, Mr. Wilson says.
That doesn't mean that you should leap into exercising with no warm-up. In addition to five minutes of gentle jogging (or biking or swimming), use "dynamic" instead of static stretches to ensure that your muscles are ready to go. For running, drills such as high knees, heel kicks and lunges are ideal.
A recently completed follow-up study by Mr. Wilson and his colleagues, using the same protocol as the static-stretching study, found that dynamic stretching had no significant effects on running performance. Other studies have also found that dynamic stretches warm up muscles effectively without dampening strength or power.
It's possible, however, that static stretching may have other benefits. But for the record, a review by the U.S. Centers for Disease Control and Prevention in 2004 of 361 stretching studies concluded that "stretching was not significantly associated with a reduction in total injuries." Subsequent reviews, most recently in 2008, have reached the same conclusion.
But this science is far from conclusive. So if you're still committed to static stretching, keep on doing it - after your workout.
Alex Hutchinson blogs about research on exercise at sweatscience.com