Stretching before exercise is harmful

I've always believed that stretching before exercise to be an annoyance -- basically a waste of time. I feel vindicated to discover that some studies show that stretching is not merely a boring ritual, but something that can actually harm you. The New York Times reports:

Researchers now believe that some of the more entrenched elements of many athletes’ warm-up regimens are not only a waste of time but actually bad for you. The old presumption that holding a stretch for 20 to 30 seconds — known as static stretching — primes muscles for a workout is dead wrong. It actually weakens them.

Rather than doing so-called "static stretching," the article recommends something called "dynamic stretching." This kind of a warm-up, of course, is not what most of us were taught to call "stretching" in gym class. It's not what people think of as stretching.

Although some studies suggest that dynamic stretches might reduce injury:

Controversy remains about the extent to which dynamic warm-ups prevent injury. But studies have been increasingly clear that static stretching alone before exercise does little or nothing to help.

The article lists some types of dynamic stretches. Basically these amount to exaggerated movements similar to those experienced during the sport. For example, the article suggests that if you play tennis:

“Spider-Man” is a particularly good drill: drop onto all fours and crawl the width of the court, as if you were climbing a wall.

To me it is interesting that so many activities related to fitness that experts have long insisted are "good for you" -- like drinking eight glasses of water -- turn out not to be so important. Expertise is over-rated.