“When it’s cold outside I find a quick ice bath sorts me out. It’s so cold that the outside conditions feel ‘warm’. It resets my resilience bar.” The words of extreme endurance athlete Sean Conway, who has run in temperatures as low as -10C. But what about more palatable ways to cope with the cold? And are there actually benefits of exercising in the cold? Why does exercising in the cold feel harder? The good news is that temperatures in the UK are rarely low enough to lead to frostbite or hypothermia. Your weekly parkrun could be slower, though, according to a 2014 statement from the British Association of Sport and Exercise Sciences: “Performance in the cold can be impaired by cooling of nerves, muscles and deep body temperature.” That same statement suggests a decrease in body temperature of 0.5C-1.5C reduces the body’s ability to supply oxygen to working muscles by 10-40%. On the positive side, you’re naturally a furnace. “Human engines are about 25% efficient,” says Dr Michael Kennedy, associate professor in the faculty of kinesiology, sport and recreation at the University of Alberta in Canada. “Much of that remaining 75% is heat. That’s the good news for warming. The bad news is that a significant sweat response means your skin gets wet.” Liquid is much denser than air, meaning saturated skin and clothing can result in hypothermia. So what should I wear in the cold? In short, layers. The basic premise is that wearing several thin garments mean you can add or remove them depending on how hot or cold you’re feeling. “Wear looser-fitting clothing to provide air pockets of heat between layers, albeit it must be breathable and wind-resistant, too,” says Kennedy. That’s extra important when cycling because of wind-chill. For instance, if it’s 4C and you’re riding at 10mph, it feels like -1C. That drops to -12C if riding at 40mph. Also wear a base layer that’s made from polyester or merino wool as this takes away (wicks) sweat from the body to the fabric’s outer surface. Other tips include: wearing clear sport glasses to reduce discomfort, like streaming eyes. “If it’s really cold, apply Vaseline on your lips and nasal passages, too, because this cuts cold exposure,” says Kennedy. Gloves are essential, though Mike Tipton, professor of human and applied physiology at the University of Portsmouth, recommends mittens because less heat will be lost. And a balaclava or a snood is a worthwhile winter investment. “Breathing cold air can trigger thermoreceptors [nerve endings that sense temperature] in the upper respiratory system that can lead to cold-induced exercise bronchoconstriction,” says Kennedy. “So, cover your mouth and nose. Plus, research has found that maintaining temperature in your nostrils preserves your ability to fight off inhaled viruses.” As for warming up: “Do this inside. One of the responses to cold is shutting down blood flow to the peripheries,” says Tipton. “Once that’s happened, it’s hard to open the vessels again. Stepping up and down a staircase for 10 minutes will get the blood flowing – but not to the stage of sweating.” I’m warmed up, what next? Layering and warming up should overcome most physiological hurdles. But what about the mechanical? “Trips and falls increase in the cold, but not solely because of the slippery conditions,” says Tipton. “If muscles and nerves cool, neuromuscular function is impaired, resulting in increasing incapacitation. The limbs are particularly affected due to their high surface area-to-mass ratio.” And don’t forget to drink. Hydration is often overlooked during the winter months because, unless you’re clothed badly, you sweat less. “That’s a mistake,” says Kennedy. “You should keep sipping during exercise for both hydration status and lung health. You lose a fair bit of water due to heavy breathing during exercise in cold air, and this needs to be replaced in addition to your normal water losses.” There’s empirical evidence that high-intensity winter efforts are worthwhile, too. A 2021 study in the Journal of Applied Physiology found that hard training at 0C increased lipid oxidation – burning fat – threefold compared to hard training at 21C. One benefit of braving the cold now is that by Christmas you’ll have become acclimatised to lower temperatures. “From a thermal comfort standpoint, we know that your body early in the winter perceives cold air as a greater stressor than later,” says Kennedy, who adds that 10 days of cold exposure alters perception so the cold doesn’t “feel” as painful. There’s further evidence that consistent periods in the cold prompt you naturally to retain more heat and raise your metabolism in an effort to generate more heat. Does cold weather exercise have additional benefits? Celebrity cold therapy advocate Wim “The Iceman” Hof suggests frequent exposure to low temperatures naturally creates a fierier furnace, as you activate a substance called brown fat. He credits brown fat with keeping him warm during his cold achievements, which include ascending Kilimanjaro dressed only in shorts. We all have brown fat – though babies have a relatively high proportion to keep them warm as they’re unable to shiver. This decreases with age. Kennedy says that the English Channel Swimming Association swimmers would acclimatise to the cold and have significantly greater “non-shivering thermogenesis” due to activation of brown fat compared to non-acclimatised swimmers. Tipton is more sceptical of its thermogenic qualities. “Brown fat generates very little heat,” he says. “Sitting down, you’re producing 100 watts of heat, so little more than a lightbulb. Jogging, you’re looking at 1,000 watts, which can crank up to about 3,000 watts when working really hard. Brown fat is about 30 watts. Then again, there is evidence that it’s good for you.” That’s supported by 2020 research in the journal Arteriosclerosis, Thrombosis, and Vascular Biology that showed activating brown fat through cold activities like winter swimming improved cardiovascular health. What if you still dread stepping in to the cold to exercise? Try reframing how you think about chilly conditions. “Think about cold as your foe and that, by dressing in a well-layered ensemble that covers all the right parts of the body, you will win the “winter malaise” battle,” says Kennedy. “I would also say that your body needs five minutes to adjust, especially if it’s windy and wet. But know that if – when – you get through that first five minutes, your body temperature and those sensory nerves will have calmed down and you’ll be more comfortable. Or you can do what I’ve sometimes resorted to. When I have low motivation, I just shout at myself to get out the door!”