You're either one of them, or you've seen them. Come into the gym or workout class and immediately begin stretching. Bending at the waist, trying to touch the floor, bouncing, putting a leg up on something high and reaching forward. It's a common sight, but is it really necessary? And, could it actually be HARMFUL??
The answer to that question is: It depends on who you ask!
Some people are in the DON'T STRETCH BEFORE WORKING OUT camp and some are in the ALWAYS STRETCH BEFORE WORKING OUT one. There is some research on both sides and the answer as to whether or not it's a good idea is not a super clear one, but let's dig into some aspect of stretching first to get a better understanding of some different types and purposes...
STATIC STRETCHING- Static stretching is simply moving into a stretched position and holding it. For instance, kicking your leg up on a table, stretching it out, and just holding it there. The point being to stretch the tendons and muscles to make them more elastic and thus help with whatever movement or activity is coming up next.
BALLISTIC or DYNAMIC STRETCHING - This could also be called BOUNCING as that's what it looks like. Someone bends at the waist and then begins to do a little bouncy motion, supposedly to help to increase flexibility with each little bounce.
FUNCTIONAL WARMUP - Ok so this 3rd one may not be a technical term for stretching, but it is a term used by lots of personal trainers. It is the philosophy of simply moving the body by starting slowly and increasing intensity to the body "warms up" naturally and the range of motion of each body movement increases as the blood flow in the body increases. So, for instance, starting with a light jog in place, moving into some jumping jacks, moving into some bodyweight squats, and maybe finishing with some high knees.
So, as you might imagine, the theory behind stretching is to increase flexibility to aid in active movement. A runner whose hamstrings are flexible will have a longer stride and thus help support their movement. A tennis player who has more flexibility and movement in their shoulders and back may be able to swing the rack harder and more fluidly, etc. And in both cases, the flexibility should help prevent injuries. Or, so the theory goes. But, what does the RESEARCH say?
The bottom line: Stretching before exercise shows no measurable positive effect on any exercise performance and depending on how it is done, may actually decrease performance and INCREASE the possibility of injury.
This is because stretching cold muscle and tendons is like quickly stretching a cold rubber band. If the band is too cold, stretching it can create tiny little MICRO TEARS which can increase the possibility that the rubber band will break. The same is true of your body. If you stretch cold, these micro tears can form as well. Instead, by slowing warming up the muscles and tendons by mimicking the activity you will be performing more intensely later, your body will naturally prepare itself for increased motion. For many, their natural range of motion is just that, and while flexibility can be increased with stretching, doing so POST warmup is likely the safer route. And for most, extreme flexibility is not even something that makes sense. A gymnast may need to perform a split, certainly, but a baseball player? A weightlifter? Nope. An athlete is likely better offer mimicking the movements they will be performing, but simply starting off slowly and increasing their intensity as their body warms up. Stretching, in and of itself, may not serve any functional purpose whatsoever.
But, don't take my word for it, here are a few hundred thousand words you can peruse in your spare time: