I’m a professional stretcher and this is the one thing I’d never, ever do to muscles

You might think that stretching, in any way, shape, or form, is simply the right thing to do, and that doing it at all is an achievement. I hate to break it to you, but this isn’t always the case. If you try and stretch cold muscles, you’re going to sabotage how well you perform in your workout.

Having “cold” muscles basically means that your muscles are the opposite of warmed up, and are not at all prepared for activity. “The concept of warming up promotes blood flow and quite literally makes them warmer,” says Jeff Brannigan, director of programming at Stretch*d in New York City. If your muscles are cold, on the other hand, they’re in a “tense” or “stale state,” he explains. On a deeper level, cold muscles means there’s not a lot of water in your muscle tissues and that your neurological system isn’t fully awake, says Eric Owens, musculoskeletal expert and co-founder of Delos Therapy.

Cold muscles tend to feel stiff—which might seem like an ideal time to stretch them, even though it’s not. “Any time you start to stretch [cold muscles], that causes a stretch reflex that gets your muscle tissue to activate a protective mechanism to not over-stretch,” says Owens. That’s what happens in static stretching before a workout, something he says all research confirms is the worst thing you can do. “If you [stretch] with your body in a cold state before your nerves are awake and your blood is pumping, it causes everything to tighten. So you’re asking your muscles to workout in a contracted state so that they’re going to have a weak and decreased performance.” And yes, it can even lead to injury.

This doesn’t mean you’re free to start sweating without stretching first. The idea is to do a proper warmup… which means dynamic movements (aka not standing there and grabbing your ankle to stretch your quad). “Before a workout, you should do a very light warmup with simple jumps, a light jog, a brisk walk—something moving,” says Owens, noting that this will get your muscles working through their range of motion. So, an important lesson for you: Stretching is not the same thing as a warmup, and choosing the right one will make all the difference in your workout.

Here’s a dynamic warmup to try for yourself:

Now, here’s a 12-move dynamic stretching routine to do for happy, ready-to-work muscles. Also try this dynamic hip stretch called the “gate opener.”