We stretch for lots of reasons: Because it feels good, because it's part of our pre-workout routine, because a muscle is stiff and we think stretching will fix it. But most of what we know about stretching -- and thus the ways we use it -- are based on wishful thinking and outdated science. We're stretching for all the wrong reasons.
Illustration by Sam Woolley
Stretching is steeped in tradition and myth. Like targeted fat-busting, it makes for catchy headlines and glib locker-room advice, but the science doesn't back up the assumptions that athletes embrace.
In many cases, stretching does the opposite of what it's promoted for. You already know that it doesn't prevent injuries. It also doesn't cure muscle soreness; in fact, aggressive stretching can cause muscle soreness. And pre-workout stretches, far from preparing you to work out, actually rob you of strength. Here's the truth behind some of those persistent myths:
Stretching Doesn't Cure Muscle Soreness
I often hear athletes asking each other, "Do you know a good stretch for this muscle?" Said before or during a workout, it's almost always because the person has a sore muscle and is looking for a way to fix it. This almost makes sense: It feels good to stretch a sore muscle. Or at least it feels like you're doing something.
But stretching doesn't provide any lasting pain relief (and it doesn't prevent soreness either). The sad truth about muscle soreness is you can't really do anything to make it go away; muscle fibres are damaged and they just need time to heal.
In fact, stretching itself can damage muscle fibres -- you're just tearing them by stretching them instead of by contracting them. If you want to stop feeling sore, aggressive stretching is the last thing you'd want to do.
Because muscle pulls (strains) feel similar to soreness, people often have the same reaction, wanting to stretch the pulled muscle. Here it's an even worse idea: the pulled muscle needs to knit back together, and stretching sabotages that process.
Stretching Robs You of Strength in the Short Term (but Is Good for You in the Long Term)
If you stretch as part of your pre-workout warm-up, when it comes time to lift that weight or make that sudden cutting move, you'll be weaker than if you didn't stretch. The effect lasts for minutes, possibly as long as half an hour.
Most of the studies that tested that idea used simple, measurable exercises, like a jump test. If you jump after stretching, you won't be able to jump as high as if you did the jump test without stretching first. The studies usually had people stretch aggressively for several minutes. Exactly how this applies to real world workouts is hard to say: a review published in the European Journal of Applied Physiology found that short, gentle stretches sometimes seem to help performance.
This, in part, is why "dynamic stretching" is popular these days. Instead of working on a single stretch for 30 seconds or more, you'll take your body through an exaggerated version of the normal range of motion. Maybe this means jogging with high knees and butt kicks, or crawling on the ground Spider-Man style.
But calling this a stretch may represent misplaced focus: maybe spending that same time doing ordinary cardio or strength exercises would have the same effect. After all, the key features of a warm-up are to get blood flowing, literally warm up your muscle tissue, and get your cells to ramp up their calorie-burning machinery (which takes several minutes to really get going).
And yet, there is a paradox: people who stretch routinely will end up stronger than people who don't. They're decreasing their strength temporarily, but building it in the long term. Why? Probably because of the muscle damage we discussed earlier. If weightlifting and stretching can both cause muscle damage, they should both cause the muscles to repair themselves stronger than they started. Stretching does cause hypertrophy -- muscle growth -- and this seems to explain why people who stretch end up stronger over time.
Stretching Doesn't Lengthen Your Muscles
Stretch a muscle and it gets longer, right? This is how we assume stretching works, but it turns out that might not be true -- which means a lot of ideas about why we should stretch are in question.
One of the leading theories is that stretching doesn't lengthen your muscles; it just changes your perception of pain, so that when the muscle gets stretched, you don't mind as much. This could explain why stretching doesn't seem to prevent injury: you haven't changed anything about the way your joints or muscles move.
It may be possible to lengthen muscles, but not purely through stretching. If you contract a muscle while it's lengthening (eccentric exercise), that seems to be the key to making muscles longer. It makes sense that some of the most flexible athletes -- ballerinas and yogis, for example -- do exactly this type of exercise hundreds of times a workout.
When to Stretch (and When Not to)
Now that we know the truth about stretching, a different set of prescriptions for stretching emerges:
- If you need strength in a workout (because you're lifting weights, or sprinting, or playing a sport that requires sudden bursts of power), skip the static stretches beforehand. Dynamic stretches make a fine replacement, but you could experiment with skipping the stretching entirely.
- If you like to stretch after a workout or on your off days, that probably neither helps nor hurts. You may increase your flexibility, and maybe your strength. (You could also stretch before a workout if you don't care how your strength in the workout is affected.)
- If you're sore or have a pulled muscle, stop stretching, or keep it very gentle. A little light cardio, such as walking, will bring a similar temporary relief from soreness without damaging more muscle fibres.
- If you want to build flexibility in the long term, stretching helps but eccentric exercise is probably a better approach: contracting while stretching.
You may look a little weird if you're the only person in your gym who doesn't stretch before exercise, and prefers to foam roll a sore muscle rather than stretch it out, but your muscles will thank you for it.