Why a summer of training in the heat could pay off this autumn

If my Strava feed is anything to go by, plenty of British runners are getting thoroughly fed up with the heat this summer, and I can fully sympathise. Looking back through my own running log over the past few months, hot weather has been a near-constant feature: PB attempts have been stifled by temperatures approaching 30°C, heart rates have been much higher than normal, hydration has required far more thought, and I've finished track races feeling as though I've almost melted. England recorded its hottest June on record in 2026, while the UK as a whole had its second hottest, so there is some justification for feeling that we've had more than our fair share of it.

After several months, it can become pretty draining, particularly when you're trying to prepare for an autumn race and struggling to judge your fitness because almost every run is being affected by the conditions. Then, just as temperatures finally start becoming more pleasant, the days begin to shorten and before long you're digging out the headtorch again. Given all this, it's easy to wonder whether it might have been better simply to take the summer off, or at least to have treated it as an extended period of easy running. There is certainly nothing wrong with taking a proper break, particularly during the hottest spells, but if you've continued training consistently through June, July and August, there are some good reasons to think that work will pay off once conditions improve.

You've built an aerobic base, even if your pace hasn't shown it

One of the most frustrating things about running in summer is seeing your pace fall while your heart rate rises, but this doesn't necessarily mean you're losing fitness. In hot conditions, your cardiovascular system has the additional job of sending more blood towards the skin to dissipate heat, while sweating reduces plasma volume as you become dehydrated. The result is that your heart has to work harder to sustain a pace that would be relatively comfortable in cooler weather, which is why trying to hit your normal easy-run pace regardless of temperature can turn an easy day into a surprisingly hard one.

The sensible response is usually to accept that you'll run more slowly, and there can actually be an advantage to this during the early stages of an autumn marathon build. You're still accumulating plenty of aerobic training, but you're less tempted to turn every ordinary run into a moderate effort simply because you feel good. When temperatures fall in September and October, the difference can be striking: the pace you were struggling to maintain at a sensible heart rate in July can suddenly feel comfortable again, and you get a much clearer idea of the fitness you've built over the preceding months.

You've adapted to running in the heat

There are also genuine physiological adaptations to repeated exercise in hot conditions. Heat acclimatisation can increase plasma volume, improve the body's ability to sweat and dissipate heat, and reduce the cardiovascular strain of exercising at a given intensity in hot weather. It's the same broad principle behind the increasingly popular use of saunas and other forms of deliberate heat exposure by endurance athletes, although simply running through a British summer is obviously a rather less controlled version of it.

It's worth being cautious about claims that heat training is effectively "altitude training for the summer", because the evidence that heat acclimatisation produces a large performance improvement once you return to cool conditions is mixed. Nevertheless, the adaptations themselves are real, and increased plasma volume in particular could have some benefit for endurance performance. There's also a more straightforward advantage for marathon runners: if you spend all summer becoming accustomed to running in the heat, you're much better prepared if your supposedly cool September or October race happens to take place on an unexpectedly warm day.

Summer is a good opportunity to work on speed

I've done considerably more track running this summer, including racing over 800m, 1500m and 3000m, and while none of those distances bears much resemblance to running a marathon, I've increasingly come to appreciate the value of doing them. Marathon training can become very focused on accumulating mileage, long runs and marathon-pace sessions, whereas summer provides a good opportunity to spend a little more time working on speed before the really specific marathon work begins.

Shorter intervals, strides, hills and track races can improve running economy, leg turnover and your ability to run efficiently at faster speeds, while also providing a different stimulus from months of steady mileage. If you've spent part of the summer running substantially faster than marathon pace, returning to 4:15/km – the pace required for a sub-three marathon – can feel much more controlled. You still need the endurance to maintain it for 42.2km, of course, but improving the amount of speed you have in reserve is useful even for a distance as long as the marathon. Especially during a sprint to the finish to secure that much-sought-after PB.

The long days make consistent training easier

This isn't a physiological benefit, but it's an important one nonetheless. The long summer days give runners far more opportunities to fit training around work and family life, whether that means running early in the morning, after work or relatively late in the evening. There are drawbacks – holidays can disrupt training and sometimes the only sensible option during a heatwave is to get up ridiculously early – but there is generally much more flexibility than there will be in November and December.

That matters because consistency is still one of the biggest determinants of marathon performance. One spectacular 100-mile week doesn't count for much if it's followed by several weeks of inconsistent training, whereas months of fairly unremarkable 50-, 60- or 70-mile weeks add up to a substantial aerobic base. If you've kept that going throughout the summer, you've already done a significant amount of the less glamorous work required for an autumn marathon.

You've already banked the miles

There's nothing wrong with runners who have used the summer to take a break or substantially reduce their mileage. After a spring marathon campaign, a period of recovery can be exactly what the body needs, and there is little sense in exhausting yourself simply because your training plan says you should be running a certain number of miles during a heatwave. But if you've managed to maintain reasonably high mileage throughout the summer without overdoing it, you begin the final part of your autumn build from a strong position.

Instead of spending September trying to rebuild basic endurance, you can gradually make the training more marathon-specific, introducing longer runs, sustained marathon-pace efforts and the bigger sessions that will determine whether sub-three pace is realistic on race day. The encouraging part is that the change in weather often coincides with this phase of training, so the same fitness that produced relatively unimpressive paces during July and August starts producing much better numbers at the same effort.

After months of hot-weather running, the first genuinely cool mornings of late summer and early autumn can therefore be a useful reminder not to judge your fitness too harshly from what you've been doing in the heat. If you've trained consistently, accumulated plenty of aerobic mileage, done some faster work and adapted to difficult conditions, you've probably achieved considerably more over the summer than your Strava and Garmin paces (and forecasts) suggest. When the temperature finally drops and the serious autumn marathon sessions begin, you should be in a good position to find out just how much.