How often have you heard someone say, "I need to stretch properly before I exercise or else I'll get injured". This is especially common in judo circles. But anyone who's observant around me will know I don't stretch before judo. Even if the first thing we do is randori, I don't stretch. There's a very good reason for it. At best, it doesn't do anything to prevent injuries and at worst, it actually hampers your performance and might lead to some injuries. All of this is backed by sports science. Don't believe?

Why don't you read this New York Times article called: Stretching: The Truth

If you’re like most of us, you were taught the importance of warm-up exercises back in grade school, and you’ve likely continued with pretty much the same routine ever since. Science, however, has moved on. 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. In a recent study conducted at the University of Nevada, Las Vegas, athletes generated less force from their leg muscles after static stretching than they did after not stretching at all. Other studies have found that this stretching decreases muscle strength by as much as 30 percent. Also, stretching one leg’s muscles can reduce strength in the other leg as well, probably because the central nervous system rebels against the movements.

Or this article from Boston University: Stretch Before Exercise? Not So Fast

Recent studies caution people away from stretching before workouts, suggesting it actually impedes your body’s performance. According to this research, runners run more slowly, jumpers jump less high, and weight lifters lift more weakly by stretching, without significantly ensuring against injury during their exercise.

And this one from Britain's NHS: Do I Need to Stretch Before Exercising?

Research suggests that stretching before exercise makes your muscles weaker and slower, even though you might feel looser. "For most performances, this would be detrimental," says Dr Ian Shrier, a sports medicine clinician and researcher and Associate Professor at the Department of Family Medicine, at Montreal's McGill University.

While you're at it, here's Scientific American: Why Pre-Workout Static Stretching Is Actually Dangerous

Muscles are made up of bundles and bundles of tiny fibers. The theory was that stretching before engaging in exercise would make the muscles' fibers more pliable and therefore less likely to get torn or strained. But in studies that have compared the rates of injury (or even muscle soreness) among people who stretched before exercise and those who didn’t, researchers found little benefit (if any) in stretching. In fact, they found that stretching a cold, tight muscle that has not already been thoroughly warmed up could actually increase the likelihood of injury. Sadly, stretching before or after exercising does not even protect you from muscle soreness. So, if you hear someone say that they’re stretching so they don’t get injured, you should let them know that scientific evidence has shown that static stretching doesn’t reduce your risk of injury. And sadly, stretching before or after exercising does not even protect you from muscle soreness.

One more, from Fitness Magazine: The Truth About Static Stretching

In recent years, a mounting body of evidence has shown that performing static stretches before a workout is like stretching a frozen rubber band: It pulls apart and weakens the fibers, says Steve Saunders, founder of Power Train, a sports training facility that works with professional, collegiate, and everyday athletes. For example, in one Journal of Strength and Conditioning Research study, researchers found that static stretching before performing a squat may reduce lower-body strength and stability. Likewise, when researchers examined 104 studies on pre-workout static stretching for a review published in the Scandinavian Journal of Medicine and Science in Sports, they concluded that static stretches reduce strength, power, and explosive performance. The authors wrote that you should avoid static stretching before a workout.

The New York Times, Boston University, UK's NHS, Scientific American and Fitness Magazine. All conclude the same thing: Don't stretch before exercise. It does not help to prevent injuries and worse still, it hampers performance.