The Science of Racing in the Cold

“There’s no such thing as bad weather, just soft people,” legendary coach Bill Bowerman once said. But however useful that is for motivating yourself to brave the elements, the reality is that weather can have a dramatic effect on performance. And it’s not just hot weather that can do it. Cold-weather racing is just as difficult and can easily set you back at least as badly.

Stephen Cheung, an environment and exercise physiology researcher at Brock University in St. Catharines, Ontario, whose experiments have earned him the nickname “Dr. Freeze,” says that while the human body can easily tolerate a rise in core temperature from 98.6 degrees to 100, 101, or even 102, (and as high as 104 for elite marathoners), “you have almost no room for error on the cold side.”

Even if your core temperature remains normal, he says, research shows that your muscles may be affected enough to cut your endurance capacity (measured as how long you can hold your target pace) by 30%. If your core temperature drops, you can tack on another 30%.

One runner who can attest to how badly even getting moderately chilled can affect you is Portland, Oregon, is runner Kristin Shaw.

She had spent months preparing for the 2024 Houston Half Marathon, expecting a nice break from Portland winter. But race day served up a chilly morning by Houston standards: 41 degrees at the start, with a 15 mph wind that produced a “feels like” temperature of 33 degrees. Shaw, who was fit, confident, and chasing a big PR, was comfortable in the first 10K of the race. Then she turned into the wind and discovered she’d underdressed. Her arms and face got cold. This quickly translated to a loss of power to her legs, even though she was wearing tights. “I felt like I was dying a slow death,” she says. “There was no fight in me.”

Her pace fell off 10 seconds a mile, then 17 seconds, until she found enough kick to salvage a 1:24:59—still a PR, but a far cry from the 1:22 she’d been targeting. “You have to respect Mother Nature,” she says. “I thought I did, but not enough.”

Your Muscles On Cold

Mike Tipton, a human applied physiologist working in the Extreme Environments Laboratory at the University of Portsmouth in England, says Shaw’s experience is a perfect example of what getting too cold can do to you. He analogizes it to a cold front going into your legs. As it penetrates deeper into your tissues, a cascade of performance-damaging things starts to happen.

They begin at the skin, where blood vessels constrict to conserve vital heat for the core. Initially, that’s mostly a problem for the extremities, like fingers and toes—uncomfortable and potentially damaging to the affected tissues, but not vital to running performance. But as the cold spreads, it starts penetrating into larger muscles like the ones needed for running.

That has multiple effects. One is that it makes your muscles and joints stiff. “The example I always give my students is if you get a fresh chicken leg and wobble it about, it’s hanging loosely,” Tipton says. “But put it in the fridge for half an hour and it’s now rigid.” Not that your legs become fully rigid, but their tissues and joint fluids become less flexible—Tipton’s term is “more viscous”—not just increasing the risk of muscle pulls, but also requiring more energy simply to contract them with each stride.

At the same time, the cold reduces the ability of your muscles to create force. That means that to maintain pace, you need to recruit more muscle fibers for each stride than normal—an effect Cheung has quantified in his lab by measuring the electrical activity of the nerves leading to them as people exercise under various temperature conditions. This, he says, can substantially increase the amount of energy needed to run at any given speed—one of the big reasons why cold muscles have less endurance.

Meanwhile, as the cold penetrates deeper, more and more of your blood vessels are constricting, a double whammy for muscles already calling for more oxygen than normal. “We’ve performed studies where we’ve had individuals cool down by [just] half a degree or one degree Celsius,” Cheung says, “and to perform the same exercise, they needed a lot more oxygen.” In one experiment, chilled cyclists had to be put on 40% oxygen, as opposed to the normal 21%. (Like many of Cheung’s studies, this one involved reducing the cyclists’ core temperature, but the same basic processes will occur if only your muscles are cold.)

The body’s enzymatic processes are also adapted to work best at normal body temperatures. “When you start cooling down, [these] slow down,” Cheung says, including the ones in your mitochondria (the body’s aerobic power plants). “So, you’re kind of hosed from both ends,” he says. “You need more energy … and it’s being produced slower.”

That produces a stronger reliance on anaerobic metabolism, a serious problem in longer races, where it can start taxing your glycogen reserves far earlier than normal. Further compounding the problem, Cheung says, is that among the extra muscle fibers being recruited in order to propel each step, it is likely that your body is relying more heavily than normal on fast-twitch fibers, which are powered solely by anaerobic processes.

Bottom line: in a long, cold race, you are likely to run out of glycogen and bonk unexpectedly early. And when you do, that is likely to make your muscles even colder, because the slower you are forced to run, the less heat they produce to fight the invading cold. “They get in a sort of vicious descending spiral,” Tipton says.

Sucking Cold Air

Other insidious effects come simply from breathing hard in cold conditions. That’s because cold air is…cold. And dry. Even if the relative humidity of the air is high, its absolute humidity isn’t. That means that when you inhale the air and warm it up, its relative humidity drops, and you easily lose water (and heat) from your lungs. “You will be breathing in colder and drier air, and your lungs do not like it,” Cheung says. “They need to be warm, and they need to be humidified.”

Worse, he says, once you get moving at even a “moderate” marathon or half-marathon pace, you will be breathing more through your mouth than your nose, “so you have less time to warm and humidify the air [before it gets to your lungs].”

A minor effect of this can be sore throats and coughs after the race. But bigger concerns, Cheung says, can be dehydration and core chilling from bringing all that cold air deep into your body.

The antidote to all of this, of course, is to accept that cold is real, and that trying to power your way through it won’t work. Shaw was determined to do exactly this when, six days after her disappointment in Houston, she flew to Richmond, Virginia, to help out her club in the masters race at USATF Cross Country National Championships.

The weather was even worse than in Houston, with the temperature hovering around 30 degrees and wind speeds of 15 mph, gusting to 22 mph. But this time, she was determined to redeem herself by dressing for the cold. She wore not only tights, but a long-sleeved insulating top. And instead of struggling at the end, she was able to summon a fast final kilometer, capped by a come-from-behind kick that propelled her into eighth-place and helped her team secure the win.

Shaw’s story proves that Bowerman, in making braving the cold simply about being tough, may have missed another important point, one Shaw recalls hearing from a family friend who was something of a Swedish second mother: “There is no such thing as bad weather, only bad clothes.”

Tips For High-Performance Running in Cold Weather

Here are 10 other tips to help keep your body functioning at its max next time you find yourself facing a long race (or training run) in chilly conditions.

1. Warm up gradually, ideally in a warmer environment.

This, Cheung says, reduces the shock to your lungs from stepping outside, and gives your body a little time to adapt. When you do step outside, continue as much of your warmup as possible in a buff or a medical mask, slowing the rate of cold air entering your lungs.

2. Avoid getting sweaty during the warmup.

If you get sweaty and then have to wait 15 minutes in a starting corral—not uncommon in big races—you could be badly chilled before you start. High-alpine climbers and polar explorers know that sweat is often the enemy, turning rest breaks into “freeze breaks.” Don’t let that be you in the starting pen.

3. If in doubt, dress too warmly.

Unfortunately, there are no hard-and-fast rules regarding what to wear when running in the cold. “Individuals tolerate cold very differently,” says Robert Girandola, a runner and retired kinesiologist at the University of Southern California. Partly, that’s due to differences in subcutaneous fat, but even non-elite runners generate and lose heat at different rates. Obviously, you don’t want to bundle up so warmly that you’re miserable, or are sweating enough to get dehydrated, but remember that the body can handle being a bit hot much better than being frozen. “I would always err on the side of being too warm rather than too cold,” says Cheung.

4. Adjust hydration and nutrition strategies.

Breathing cold air for hours on end can be surprisingly dehydrating, so don’t think that just because you aren’t sweating much you aren’t losing fluids. Likewise, realize that in cold weather, you are probably burning more glycogen than normal. Plan accordingly.

5. Don’t emulate the elites.

Just because they’re stripped down for the race doesn’t mean you can do the same. Not only are they not going to be exposed to the elements for as long, but they are generating a lot more energy per minute—energy that can help keep them warmer. “It’s [another] double whammy,” Cheung says, “because you’re not generating as much heat, and you’re also out in the cold for four or five hours, as opposed to an elite marathoner.”

6. Don’t worry that extra clothing will slow you down.

How much does an extra pair of tights, or a long-sleeved top actually weigh? How much do they really impede movement? Maybe a little, Cheung says,  but the effect really is minimal, “and the benefits can be so much more.”

7. Don’t think you can adapt to cold by practicing in it.

The body is quite good at adapting to heat. To cold? Not so much. Mostly, the things we think of as adaptations are a matter of becoming desensitized to disliking how our skin feels, and have nothing to do with how our muscles function. “It’s perceptual,” Cheung says.

The only thing that does appear to adapt to cold, Tipton says, is peripheral blood flow, which can shut down slower with repeated exposure to cold. That may keep your skin warmer for a while and contribute to making cold temperatures feel less unpleasant, but once it is overwhelmed by the cold, the same cascade of performance-impeding effects will still occur.

8. When feasible, start upwind.

This, obviously, isn’t possible in races, but in training, it’s a good way to make sure you’re not underdressed. If you do get cold, you can turn around and run back to shelter, downwind. If that’s not possible, make sure you are slightly overdressed for the downwind segment at the start, so you don’t get an unpleasant surprise when you turn around.

9. Protect your arms.

We run with our legs. But we also use our arms, and if they become chilled, that can, as Shaw discovered, make our entire bodies have to fight harder to overcome the cold. They are also particularly easily chilled, Tipton says, because they are thin compared to the legs and moving rapidly as you pump them, increasing their wind chill.

10. Men, guard your groin.

It is possible to severely chill or even cause frostbite in certain delicate parts of the male anatomy, particularly when running into a headwind in thin, damp running shorts. This is not a pleasant experience. Windproof shorts and tights are designed to prevent this, but a low-tech solution is to stuff a lightweight sock into your underwear. A bit like a silly Shakespearean codpiece? Yes. But far better than the alternative.