The problem is, people confuse warming up and stretching. And more than that, they confuse static stretching and dynamic stretching.
Warming up -- which involves raising your internal core temperature and taking your body through dynamic, full range of motion movements -- definitely helps prevent injury. Some of these movements (think lunges, skipping, air squats, and arm circles) are actually considered dynamic stretches. When performed as part of a total warmup routine, they’re incredibly beneficial, and can, in fact, help prevent injury.
But standing still and touching your toes like in high school gym class? Not so much.
Stretching after exercise reduces soreness
Look, I’m not knocking a good, post-workout stretch. In fact, stretching after a workout, when your muscles are warm and limber, is a great time to take yourself through a stretching routine to maintain, or even improve, your flexibility. But if you’re relying on your stretching routine to help reduce the delayed onset muscle soreness (DOMS) that typically rears its ugly head 24 to 48 hours post-workout, you’re barking up the wrong tree. In fact, static stretching post-workout not only does nothing to reduce muscle soreness, but it may actually lead to muscle soreness, if you hold a stretch for long periods of time.