Stretching: The Truth
While no one would argue that a good diet and a reasonable training schedule are invaluable in preventing injuries, there’s a surprising amount of controversy regarding the role of stretching. Some people swear by it, while others shun it. Of those who do stretch, some emphasize stretching before working out, while others stretch only after exercise. Let’s look at what research says about stretching’s role in preventing injuries.
In the largest study to date questioning the importance of stretching1, researchers evaluated the effect of pre-exercise stretching on 1,538 military recruits during a 12-week training program. One group of recruits performed a series of 20-second stretches on each of the six major muscle groups, while the remaining recruits were told to avoid all pre-exercise stretching. At the end of the 12 weeks, there was no difference between the two groups in injury frequency. This finding is consistent with several other studies that have demonstrated that stretching, particularly stretching before activity, plays little to no role in injury prevention. In fact, several studies have suggested that stretching may increase the risk of injury, on the grounds that a stretched muscle is less coordinated2 and temporarily weakened.3
Unfortunately, there’s a problem with the majority of studies questioning the importance of stretching: the stretches used in the research were performed to the point of pain and/or they were done immediately before activity.123 To help resolve some of the controversy regarding the importance of stretching, researchers evaluated 70 Australian rules football players for two years to determine their rates of hamstring injuries.4 Then, the athletes were studied for another two years, during which time they were told to perform a specific stretching program. Unlike in other studies, the athletes were told to avoid pre-exercise stretches. They were instructed to gently stretch the hamstrings for 15 seconds with the knee bent at various angles (0, 10 and 90 degrees), and they were told to stretch after training, when the hamstrings were fatigued. The authors believed that stretching a fatigued muscle would improve the muscle’s ability to absorb shock when it was most prone to injury—that is, when it was tired.
At the end of the study, the stretching program decreased hamstring injury rates from an average of 10 athletes per season to three athletes per season. Also, the number of days lost from competition was reduced from 35 days in the no-stretch group to 10 days in the stretching group. The findings of this study are consistent with others demonstrating that muscle tightness is a predictor of injury5 and that increasing flexibility by stretching reduces injury rates.6
In one of my favorite articles on injury prevention7, researchers measured a variety of variables in two groups of runners. One group had sustained at least one overuse injury, while the other group was that rare breed of runner who had remained injury-free throughout their entire running career. After taking a variety of measurements and evaluating both groups with high-speed cameras as they ran over force platforms, the only anthropomorphic difference between the two groups was that the lifelong injury-free group of runners demonstrated significantly more hamstring flexibility. (They also had a tendency to strike on the outside of the heel and pronate faster, which will be the topic of another article.)
It appears, then, that properly applied stretches may reduce the frequency of injury. But for how long should a stretch be held? How much force should be applied during the stretch? To help resolve these questions, researchers studied the behavior of rabbit tendons exposed to various amounts of force held for different lengths of time.8 The researchers concluded that ballistic or bouncing stretches should be avoided, because they load the muscle too rapidly, and thereby predispose it to strain. They also concluded that static stretching, performed with mild to moderate force and held for 30 seconds, effectively increases muscle length. The researchers determined that the vast majority of muscle-length gains occurred in the first 15 seconds of a stretch, and that when a 30-second stretch was repeated 10 times, the majority of length gains occurred in the first few stretches. In fact, no additional gains were made between the fourth and tenth stretch.
Keep in mind that there are several ways to improve flexibility besides simply passively stretching a muscle. The most popular alternatives to static stretches are proprioceptive neuromuscular facilitation, or PNF, stretches. These stretches incorporate a variety of gentle pre-stretch muscle contractions of either the agonist or antagonistic muscles; this method warms the muscle gradually before beginning the stretch. By doing so, it’s possible to get an increased range of motion without the risks associated with forceful passive stretching (e.g., weakness and impaired coordination).
Another common method of improving flexibility uses prolonged gentle stretches that are held for extended periods of time. The theory with this stretching technique is that, by lessening the force associated with short-term passive stretching, the negative side effects of stretching can be avoided, while the muscle and the surrounding fascia gradually lengthen with the application of very gentle forces. In one study evaluating the effectiveness of conventional static stretching versus prolonged low-force stretching in the treatment of chronic plantar fasciitis9, prolonged gentle stretching, which incorporated a brace to stretch the calf for extended periods of time, outperformed static stretching; the prolonged-stretch group had significantly greater reductions in pain, fewer follow-up visits and fewer additional total interventions. Prolonged static stretching is so effective at restoring range of motion even in the most difficult cases that it is frequently used to restore flexibility after total knee replacements when conventional static stretches aren’t enough.
The lessons to be learned from these studies are clear: avoid pre-exercise stretching, and never stretch to the point of discomfort. A proper warm-up consists of slowly jogging (or even walking) for the first five minutes of your run, followed by a few light stretches. This approach increases circulation and warms your muscles gradually without overstressing them.
After your run, perform a few 15- to 30-second stretches on each of the major muscle groups. Never push the stretch to the point of discomfort. It is better to hold a stretch for 15 seconds and repeat it throughout the day than to spend long periods stretching specific muscles. As with most things in life, the key to injury prevention comes down to moderation: moderation in exercise intensity, and moderation in stretching intensity and frequency. The rewards of running injury-free are well worth it.
4: Verrall GM, Slavotinek JP, Barnes PG. The effect of sport specific training on reducing the incidence of hamstring injuries in professional Australian rules football players. Br J Sports Med 2005;39:363-368.