I was in France last week. Thirty degrees, every day. It was hot enough that running there was genuinely tough, the heat and humidity sat on you from the first step. But here’s the thing about training somewhere like that in summer, everyone’s out. Runners, cyclists, people walking before it gets too warm. Bright sunny mornings make motivation easy. You don’t have to talk yourself into anything.

I got back to the UK and the day I landed, the storms rolled in. Biblical rain. I still had a two hour run on the plan, intervals, so I went and did it. After all, the skin’s waterproof.

In honesty, it was pretty miserable. Intervals in the pouring rain means a lot of starting and stopping, a lot of standing around getting colder between reps, no rhythm to hide inside. I won’t pretend I enjoyed it.

No, the rain doesn’t make you fitter

Let’s get the honest bit out of the way first, because I try not to sell people things that aren’t true. I don’t think there’s any real evidence that running in the rain or the cold makes you fitter than running in good conditions. The fitness comes from the training itself, the consistency, the volume, the intensity, done week after week, year after year, regardless of what the sky’s doing.

What the weather does give you is something else entirely, the chance to keep that consistency going when it would be easier not to.

The toughness is real, even if the fitness gain isn’t

Where the research does back things up is mental toughness. Training in genuinely uncomfortable conditions, heavy rain, cold, wind, teaches you to push through discomfort in a way that a climate-controlled gym never will, and that resilience doesn’t stay on the trail, it carries into the rest of your life too.

There’s a study from 1999 in The Psychological Record that’s stuck with me since I read about it. Researchers found that pain tolerance didn’t come from trying to think your way out of discomfort with positive self-talk. It came from acknowledging the discomfort was there and not fighting to change the sensation. That’s more or less what running intervals in the pouring rain teaches you without you realising it’s happening. You stop trying to convince yourself it’s fine. You just let it be uncomfortable and keep moving anyway.

I’ve run in some genuine extremes over the years, high thirties heat, minus nineteen cold, everything in between including yesterday’s soaking. The truth I keep coming back to is that if you want to be consistent, you don’t get to choose the weather. And that’s exactly where the benefit is hiding.

Your body works harder than you think

There’s a physical case for it too, even if it’s not the one people expect. In the cold, your heart has to work harder to pump blood around your body and keep your core temperature stable, and over time that extra demand can improve how efficiently your body regulates temperature and shifts oxygen around, which is part of why so many endurance athletes swear by the old line, if you can train on a filthy, freezing morning, a sunny spring race day feels easy by comparison.

Cold exposure has some interesting effects on the immune system too. One study on winter swimmers found they had a 40% lower rate of upper respiratory infections than people who didn’t swim through winter. Another found that a short swim in cold water gave a measurable boost to white blood cell count. I’m not saying stand in the rain to dodge a cold, but there’s more going on physiologically than “you’ll just get wet and miserable.”

The mind benefits too, not just the body

There’s also decent research on outdoor exercise and mood that goes beyond the obvious. One study comparing outdoor hikers to people walking the same effort on a treadmill indoors found the outdoor group reported more calmness, more contemplation, more genuine positive feeling, and less fatigue, even though the physical effort was comparable. Something about being outside, exposed to the actual conditions, changes how the effort feels and what you get back from it.

And this is the part that doesn’t get talked about enough. Doing things you don’t want to do, consistently, is part of what builds discipline in the first place. Not just tolerance for one specific discomfort, but a broader identity shift, you start to see yourself as someone who does the hard thing rather than someone who waits for good conditions.

Building the edge

Here’s my honest motivation, stripped of any research. I don’t like running in the pitch black in a UK January at minus four. But I like knowing that not many other people will be out there doing it. I like knowing I’m building an edge, separating myself from the average mindset, one uncomfortable session at a time. That’s genuinely all the motivation I need.

Bad weather isn’t a training hack. It won’t make you faster on its own, and I’d never tell you it will. But it strips away the excuse of waiting for the right conditions, and it quietly builds the kind of consistency and toughness that shows up everywhere else in your life, not just on the days it’s raining.

So no, the rain didn’t make me fitter yesterday. But showing up in it, again, is exactly why I’ll still be capable of showing up in ten years’ time.