Why does running feel easier in the cold?

By Sam Carey, Founder of Run Love Sprint.

Most runners have noticed it at some point. You head out on a crisp winter morning, a little reluctant to leave the house, and somewhere in the first mile you realise the run feels easier than it has for months. You're moving faster without trying, you haven't broken a sweat, and the effort that felt like a slog in August suddenly feels manageable. With the clocks going back and the colder months setting in, I wanted to understand why, and a short paper from two physiologists offers an interesting answer.

The research

The paper, Why is it easier to run in the cold? (opens in a new tab), was written by Yaroslav Molkov and Dmitry Zaretsky and published in the journal Temperature in 2016. It's a commentary rather than a large study, and it builds on the authors' own earlier laboratory research, Exercise activates compensatory thermoregulatory reaction in rats (opens in a new tab), published in the Journal of Applied Physiology in 2015.

The starting point is personal. One of the authors is a marathon runner, and when he looked back over several years of his own training logs, his average pace in the winter months was around a minute per mile faster than in the summer. He'd also noticed what many of us have, that it can take much longer to start sweating on a cold day, even when you're running faster and wearing more.

Why heat matters

The authors explain that overheating is one of the main things that limits how hard we can exercise. When your core temperature climbs high enough, your body treats it as a signal to ease off, so the longer you can keep your temperature away from that threshold, the longer you can keep the effort up.

Running generates a huge amount of heat. Muscles aren't very efficient, and more than 80% of the energy they produce is lost as heat rather than movement. You might expect the body simply to dump that heat through the skin, but sending more blood to the skin means less going to your working muscles, which is one reason the body holds off on that until your temperature is already quite high.

What they found

This is where it gets interesting. When you're standing still in the cold, your body burns extra energy just to keep you warm. The researchers found that the moment exercise begins, the body switches that extra heat production off, before your temperature has even started to rise. The heat your muscles are producing takes over the job of keeping you warm, so the body doesn't need to generate its own on top.

In their experiments, rats ran on a treadmill at four different speeds in two different room temperatures. In the cooler room, their core temperature actually dipped slightly in the first few minutes of running before it began to climb, and it rose more slowly overall. In the warmer room there was no extra heat production to switch off, so there was nothing to offset the heat from running, and temperature rose faster the quicker they ran.

The colder the conditions, the more of this "warming" heat there is to switch off, and the longer it takes for your core temperature to reach the point where you start sweating and, eventually, slowing down. The authors' model suggests that in cold enough conditions, core temperature could stay below its starting point for an entire run.

What this doesn't mean

It's worth being clear about the limits here. The experiments were carried out on rats, and much of the explanation comes from a mathematical model rather than direct measurements in people. The minute-per-mile difference comes from one runner's training log, which is a nice observation but not evidence on its own. This paper doesn't prove that cold weather makes humans faster. It offers a plausible mechanism for something many runners already feel, and one that would be worth testing properly in people.

My take

I find this genuinely useful, partly because it explains why the first few minutes of a winter run feel so cold and then suddenly don't. Your body is quietly handing the heating over to your muscles. It's also a good reason not to overdress. If you leave the house feeling comfortably warm, you'll probably be too hot ten minutes in, because the system that was keeping you warm at the door switches off as soon as you start moving.

It also says something about summer running. If heat really is one of the main brakes on performance, then a slower pace on a hot day isn't a sign you've lost fitness, it's your body doing exactly what it should. Winter is a good time to enjoy runs that feel easier, but be kind to yourself when the warmer months come back round.

And if the darker evenings are putting you off, this is your excuse to get out there. Wrap up sensibly, wear something bright, and enjoy the time of year when running feels at its best.

This article is for general information and isn't a substitute for advice from a healthcare professional.