This article originally appeared in the March/April 2017 issue of Triathlete.

The trouble with those early- and late-season tris? The water temp is somewhere between chilly and just plain OMG. If the water’s too cold, USAT won’t let the swim happen—below 51 degrees is the cutoff for a sprint, and 53 if it’s 1,500 meters or longer. But for some people, even water temperatures in the 70s can make your body lose heat faster than you produce it—after all, water conducts heat away from your body 70 times more efficiently than air does.

Beyond being uncomfortable, cold muscles and a low core temperature make you slow, hungry and tired. While everyone responds to cold-water swimming a little differently—some people feel exhilarated and hardly bothered while others develop hypothermia quickly—researchers and practiced cold-water swimmers suggest that most people should be able to train themselves to get better at swimming in cold water, be safer and mind it less. Start with these smart training moves.

Tame those first shocking moments.
“Just jumping into very cold water causes a whole host of responses that don’t help one’s swim ability,” said John Castellani, Ph.D., research physiologist at the U.S. Army Research Institute of Environmental Medicine. As soon as you hit it, receptors in your skin fire up your body’s cold-shock mechanism: You lose control of your breathing and end up gasping and hyperventilating. Your heart starts racing, your blood pressure goes up, and your stress hormones soar. It can take about two minutes to get control over everything again.

Fortunately, you can do some prep work to take some of the drama out of that natural response. Research has shown that after about five sessions of being exposed to really cold water (about 53 degrees) for just five minutes, that cold shock response diminishes by about 50 percent.

Just don’t put your face in—you’ll automatically hold your breath, which works against your ability to regulate your breathing back to normal. Not practical because there’s no plunge pool nearby? Cold showers can do the trick, Castellani said.

If you do nothing else to train for the cold water, at least do this. The bonus: Once you’ve put the work in, the effects stick around for as long as seven to 14 months.

Train your body to be a better thermos.
It takes much longer for your body to make other adaptations that help you feel and perform better in cold water than it does to train the cold-shock response. With lots of practice swimming in colder water, your body eventually waits longer and longer to kick shivering (its genius internal reheating system) into gear. It learns to lose less heat through the limbs—it might even teach itself to use new pathways to move blood around your body—and you’ll stop feeling cold so quickly. (Sounds great, but the flip side is that you can get too good at not feeling the cold, which invites hypothermia. Know the signs: Increased shivering and an inability to think well—you can’t say your name, for instance—plus confusion, clumsiness and lack of concern about your condition.)

So how much practice do you need to make this happen? To the frustration of Type-A athletes everywhere, there’s no magic number of immersions, distances or workout lengths that makes it happen. But based on what they know so far, scientists recommend this:

Do your regular swims in incrementally colder water. That’s ideal. But if you can’t, try doing your quality training in the pool. Then, outside, swim in colder water as long as you can stand it (see “Do. Not. Do. This. Alone.” below). Get out and get warm. Then go back and do the same thing later that day or the next day, said Castellani. Do that as consistently as you can, and you’ll notice that your tolerance gradually changes.

Channel swimmers say it takes weeks or months to acclimatize, but keep in mind you’re not going to be in there as long as they are. “To get the kind of adaptations you want, you might need at least 30 to 45 minutes of exposure to water that’s the temperature you’ll be swimming in on at least 10 occasions,” said Michael Tipton, Ph.D., professor of human and applied physiology at the University of Portsmouth. “But we honestly don’t know yet.”

Don’t torture yourself … If your race is in 60-degree water, it doesn’t do you extra good to swim in 50-degree water. It only makes your sessions shorter.

… but don’t assume that “close is good enough.” “Adaptation to cold is very specific to the temperatures you’re exposed to,” said Tipton. When people’s bodies got used to a certain water temperature, those same bodies acted like all that adaptation had never happened when they hit water that was as little as 2 degrees colder than what they’d trained in.

Swim, don’t just sit. When you sit in water, you develop a warm little cocoon or “boundary layer” around yourself (that’s why Titanic victims who stayed put fared better than those who swam). That’s nice and comfy, but you’re not going to have its benefit in a tri. Train in the most realistic circumstances you can create.

Kick. Exercise with your arms can lead to greater heat losses than exercise with your legs. The arms have a greater surface-to-mass ratio (not as much muscle as the legs), and the more you work them, the more blood flows there—and the more heat you lose. If you’re worried about getting cold, learn to maximize your kick.

Lose the idea that you’ll be toasty. When you acclimatize, it’s not like you’re never going to feel chilly again. Even channel swimmers and ice swimmers are aware of the water being cold. They just learn to avoid fighting it or feeling beaten down by it.

The F-Word

Fat. The word strikes fear into athletes in a sport known for its low-body-fat elites. Do you have to carry extra to be a successful cold-water swimmer? For long-distance swimming where you’re losing heat, it helps. But otherwise, it depends on how fast you are and how long you’re going to be in the water. People with more insulation tend to maintain their core temperatures better than lean people. But you don’t have to go on an extreme weight gain program for a little extra warmth. One study found that people carrying 16 to 19 percent body fat (still pretty lean by regular people’s standards) were a little warmer in water than people with 12 percent body fat. Best places to have a little fat layer (for these purposes): upper arms, thighs and neck, says Tipton. Got a little extra on your body right now? Thank it.

Words of Wisdom from Extreme Cold-Water Swimmers

English Channel swimmers say:

“There are no shortcuts. You have to do the cold-water acclimatizing/training, just like you have to do the rest of your training.” —Dan Boyle, New York City-based triple-crown swimmer

“I’ve found consistency to be the key. When the water is very cold (sub-50), it’s not safe to immerse for longer than a few minutes—if that—for most people. Frequent and regular exposure can increase that tolerance rapidly. I’ve seen a number of Channel swimmers begin with two 15-minute swims the first day and some of the more experienced are going 30 to 45 minutes by the third day. I think shorter, more frequent and consistent exposure to colder water temperatures is the most effective way to start and build acclimatization.” —Anne Cleveland, San Diego-based distance-swimming coach and former world record holder for oldest person to complete a two-way English Channel swim  

Ice swimmers say:
“You’re never going to find warmth; you just face the cold straight on. You get to a point, like in any endurance sport, where you just accept how the discomfort feels. In fact, when you get used to swimming in cold water, that feeling can be euphoric.” —Ice swimmer Melissa O’Reilly, founder of MostExtremeSwims.com, a tour company that helps swimmers get to ice-swimming races (you know, where they “build” a pool by chain-sawing its dimensions into the ice). O’Reilly isn’t a naturally warm person—she succumbed to hypothermia in a distance swim with water in the low 60s but has since become a world champion ice swimmer.

Do. Not. Do. This. Alone.

You might be an Ironman (congrats), but Mother Nature’s even stronger than that, and you can get better at working with her, but you can’t change her mind. So you have to be alert to when she’s telling you that your training swim is over. And you’re not always going to be the first to notice. Your body is good at perceiving skin temperature but not core temperature, which can drop without you being aware of it. At the same time, hypothermia makes you clumsy, apathetic about your situation, confused and maybe even nauseous and unable to speak without slurring your words. Promise us you’ll never train in cold water without someone else going along. They can be in a kayak or a rowboat or right in there with you. But no swimming alone. Ever. But especially in cold water.