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Milling around before the start of last month’s Under Armour Spring Run-Off 8K with a few thousand other runners, I couldn’t help noticing all the different prerace rituals on display: jogging, sprinting, hopping, skipping and so on. The scene was a little different – more dynamic – compared to what I remember from my first road races two decades ago, when toe-touching and other sedate stretching poses were all the rage.

We’ve all been told that warm-ups and cool-downs are the crucial bookends to every workout – but ideas about what constitutes a “good” warm-up or cool-down have shifted over the years. Here’s a look at what the latest science says about how to start and finish your exercise sessions.

The warm-up

A warm-up generally has two main goals: to boost your performance, and to reduce your risk of injury or next-day soreness. For performance, surprisingly, “evidence for the effectiveness of warm-ups isn’t overwhelming,” says Kerry McGawley, a professor at Mid Sweden University’s Swedish Winter Sports Research Centre who studies the topic.

McGawley and her colleagues recently completed a study that compared a long warm-up protocol with a shorter one prior to a cycling endurance test. Neither warm-up enhanced performance compared to no warm-up at all—a result that echoes the non-findings of some (but not all) previous studies.

In theory, raising the temperature of your muscles should offer several performance benefits: it speeds the conduction of nerve signals from brain to muscle, accelerates metabolic reactions that fuel muscle contraction and enhances blood flow and oxygen delivery. But more isn’t always better.

“There is, of course, a trade-off between ‘preparing’ and ‘fatiguing’ with a warm-up,” explains McGawley. Getting your muscles revved up may be helpful, but it also generates muscle fatigue and burns valuable energy that you might need later. Finding the right balance is tricky.

For shorter or more explosive activities like sprinting and lifting weights, on the other hand, fatigue is less of an issue and studies find a consistent performance benefit from warming up.

Minimizing injury risk is a higher priority for most of us, but here too the scientific evidence is mixed at best.

The traditional theory was that static stretching, which involves holding a position such as touching your toes for 30 seconds or more, would expand your range of motion and reduce subsequent injury risk. But dozens of studies have failed to demonstrate any clear injury-protection benefits from stretching – not counting activities like ballet or kickboxing that require extreme flexibility.

However, the temperature increase associated with a good warm-up, with or without stretching, makes your muscles and tendons more supple, much as warming up a ball of plasticine in your palm makes it more malleable. There’s some evidence that this does offer some protection against subsequent injury, particularly for explosive activities.

To get these benefits, sports scientists suggest a three-stage warm up:

  1. First, at least five to 10 minutes of aerobic exercise to increase body temperature.
  2. Second, mobility exercises that take your muscles and joints through the range of motion they’ll encounter during the workout, such as skipping with high knees before running or lifting light weights before strength training.
  3. Third, a brief period of activities that mimic the movements and intensity of the coming workout, such as sprints before running or shooting and passing drills before a soccer game.

The cool-down

The postworkout cool-down is another topic with sparse scientific evidence, McGawley says.

One myth that has been debunked is that the cool-down will prevent next-day soreness. That soreness results from microscopic muscle damage during the workout, and there’s nothing you can do afterward to “undamage” the muscles. It’s the warm-up rather than the cool-down that can minimize next-day soreness, as a 2007 study demonstrated – so opt for an ounce of prevention.

If you do want to stretch to improve your range of motion, doing it after the workout, when your muscles are warm and flexible, is the best time, McGawley says. But, as Portuguese sports scientist Jose Afonso argued in an opinion piece last year, that postworkout stretching should be viewed as something you can do if you enjoy stretching, rather than something you must do to optimize performance or health.

Science aside, there’s something to be said for ending your workout with a light and pleasant effort rather than the hardest effort of the day. American track coach Steve Magness encourages his athletes to think of the cool-down as a time for “social recovery,” chatting with friends in order to decrease stress hormones and boost recovery hormones.

Alex Hutchinson is the author of Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance. Follow him on Twitter @sweatscience.

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