Sunday, November 30, 2008


Recently, a New York Times article summarized some research by the University of Nevada that concluded that static stretching for 30 seconds decreased muscular power of the leg muscles of those that stretched versus those that did not. Vertical jumping and torque was unchanged.Power is the application of work within a finite time. Torque is the application of force and does not require movement unlike work. It is important to remember that athletes have different requirements depending on the sport and stretching should be sport specific."Athletes typically include static stretching as a part of the warm-up, but the evidence is clear that this practice will decrease performance in sports that require explosive movements," said UNLV kinesiology professor and study co-author Bill Holcomb, who directs the university's Sports Injury Research Center. He concludes stretching should be done after sports activity. When I asked Bill Holcomb to elaborate on his conclusions he said “The type of stretching to warmup should be dynamic rather than static to prevent a reduction of power. Then, after activity and during the cool down, static stretching can be used to improve range of motion/flexibility for later performance. “ Warming up is also something that can be overdone at the expense of performance.
“There is a neuromuscular inhibitory response to static stretching,” says Malachy McHugh, the director of research at the Nicholas Institute of Sports Medicine and Athletic Trauma at Lenox Hill Hospital in New York City. The straining muscle becomes less responsive and stays weakened for up to 30 minutes after stretching, which is not how an athlete wants to begin a workout. Another support to the idea of the inhibitory response is that the other side of the stretched leg has been shown to have less power.Stretching muscles while moving, on the other hand, a technique known as dynamic stretching or dynamic warm-ups, increases power, flexibility and range of motion. Muscles in motion don’t experience that insidious inhibitory response. They instead get what McHugh calls “an excitatory message” to perform.
Citing earlier studies, Stacy Ingraham, an exercise physiologist at the University of Minnesota, Twin Cities, says that, "When you stretch, you lengthen muscle fibers. It then takes longer for messages from the brain to travel through them. Stretched muscles also seem to be more sluggish than un-stretched ones. They don't spring back as readily. And every time you stretch, you may be tearing your muscle fibers a tiny bit." Flexibility is speed specific. There are two kinds of stretch receptors, one reacts to magnitude and speed and the other reacts to magnitude only. This also explains why it doesn’t make sense to static stretch prior to dynamic activity.
These receptors are also responsible for the stretch reflex which counters in the opposite direction to the part being stretched.
I have talked with athletes and yoga instructors about overstretching before explosive sports such as soccer and the possibility of too much laxity creating instability and a setup for injury. Clearly there is a balance between how much stretching is done.
This puts into new light the concept of devices such as night splints that use static stretching for structures like the plantar fascia that are already injured. The difference here being that the part is injured and immobilization, a time honored strategy is part of the treatment and the fascia is put at physiologic tension which is not as forceful as a true static stretch. The athletes that use a night splint are also more likley to have a flexibility deficit in the achilles tendon.

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