Five tips for running in hot weather

Apparently the weekend was especially hot in the UK, and some of you who were racing or running found it a struggle. Meanwhile, where I am, it’s been no less than 35C for months, and frequently as high as 40. That makes running a real challenge, even early in the morning or late in the evening. So, whether you’re struggling in England’s heatwave or trying to train in a hot country, here are some tips:

1. Pick your time and place 

It should go without saying that, on a hot day, you want to avoid running at midday but, with proper planning, you can be even more tactical than that. Mornings are often cooler than evenings, but you can look at the forecast and work out the best time to run based on the balance of temperature and sunlight that you require. It’s also worth thinking about your route, though – a long run across open hills may sound appealing but if there is no shade, nowhere to buy more water, and limited opportunity for rescue if anything goes wrong, it might not be the best idea for the hottest day of the year. Consider where there will be shade, how much water you will need and how you will replenish it, and how you will bail out if you start to struggle.

2. Wear the right kit

Experienced runners already know not to run in cotton shirts, but this is especially important when it’s very hot. Let’s start from basics – sweating cools you down by evaporation. It’s not the fact of having water resting on your body that makes you cool, it’s the process of that water evaporating into the air. It therefore follows that to cool yourself most effectively, you want to sweat profusely while allowing the sweat to evaporate as quickly as possible.

So, the problem with cotton, for those of you who don’t know, is that it is not an effective wicking fabric. In other words, it absorbs moisture rather than moving it rapidly to the outside where it can be dried off by the wind. The result is that a cotton shirt will quickly become drenched by sweat. Once it is drenched, it can no longer absorb more sweat, and the effectiveness of sweating as a cooling mechanism will be massively decreased. In addition, when you stop you will be wearing a wet tshirt which can make you cold surprisingly quickly even on a hot day, as your body naturally cools down after exercise.

The alternative, a ‘technical’ wicking fabric, usually a polyester blend but merino wool also works well, rapidly pulls moisture away from the body and to the edge of the fabric, where it can be dried by the air, thereby allowing your natural sweating mechanism to be as effective as possible. It will also mean the tshirt is relatively dry at the end of your run.

So, wear technical fabrics. But what else? Well, while the temptation is to wear as little as possible, whether that’s going down to a vest or even taking your shirt off altogether, this may not be the best option. A lightweight wicking fabric over your skin can actually cool you more than bare skin, partly for the reasons given above, and partly because it simply keeps the sun off. Burning is a real danger when running, and can contribute to a heat injury, so on the hottest days consider wearing a lightweight but long-sleeved shirt, or a t-shirt and slip-on ‘arm coolers’. Try also to cover up the back of your neck, whether that is with a broad-brimmed hat, or a buff, or anything else. I found when running the Paris marathon on a very hot day a few years ago that wearing a buff round my neck and soaking it with cool water every so often made a huge difference to my comfort and kept me cool very effectively.

Finally, don’t forget sunglasses. Squinting against the sun actually uses up a surprising amount of energy and will exhaust you quicker than you might expect.

3. Hydrate, but don’t only hydrate

Most people can figure out that they need to drink water on hot days. Your body will make that pretty clear to you. However, some people are less aware of the risks of only drinking water. Hyponatremia is a serious medical condition that can and has killed marathon runners on hot summer days in the UK. It’s sometimes misconceived as being a problem caused by too much water, but that’s slightly misleading as what actually kills is a low sodium level. It is, however, true that this is brought about by replacing fluids lost through a high sweat rate only with water. This causes the sodium level in the body to drop, creating symptoms that are unfortunately not dissimilar to dehydration, which can prompt the affected person to drink more water, making things worse.

Fortunately, for those who are aware of the risk, the treatment is not complex; it is simply a case of ensuring that sodium lost through sweating is replaced by an electrolyte drink and/or taking salt tablets at regular intervals. On a hot day, if you know you have been drinking regularly, be aware that dehydration-like symptoms could be hyponatremia and rehydrate with a sports drink containing sodium, or with salt tablets.

This, by the way, is one of the only times I honestly recommend drinking a sports drink. And it should ideally be an electrolyte drink, not an energy drink. That’s just me though – I can’t stand most sports drinks.

In addition to this, think about your food/gel consumption. Hot weather and exercise can suppress the appetite and/or make you feel nauseous so it may be harder to take on foods than usual, and this could have a knock-on effect on your performance. If you have the chance, try something that is less sweet than usual (Gu gels do some salty and even bitter or sour options), or even a salty snack like mini-pretzels if there’s any way to get your hands on them.

Carrying all this water, juice and gels can be a challenge so this is when I really appreciate a good running belt or ultra vest. Read my Osprey Duro 1.5 review if you’re interested in my preferred option for this.

4. Expect to struggle, but expect to acclimatise 

Those of us who come from a reasonably cool/temperate climate like the UK will always struggle if we suddenly end up running on a hot day or in a hot country. Your heart rate and perceived exertion will almost inevitably be higher for a given pace, and that can be frustrating when you find you just can’t run as fast as you are used to, especially if that happens on race day. However that is just physiology and there is no letting it get to you or, worse, assuming that because you can run at a given pace on a 20 degree day you should run at the same pace on a 30 degree day and pushing yourself to do so despite all the warning signs of your body telling you to take it easy. You should expect to find it harder, acknowledge this, and adjust your race or training plan to allow for it.

However, the good news is that you can also expect to acclimatise. The body adapts reasonably well to hot climates in a relatively short space of time. Just a few days of moderate exercise at a given temperature will be enough to undo most of the negative effects mentioned above, and with a couple of weeks of careful build up you can be fully acclimatised and expect to perform as well as you would at your ‘home’ temperature. So if there is the opportunity to acclimatise, whether it be by getting out to the race country early, running in a (properly managed and monitored) heat chamber before hand, or simply spending some time in a sauna in the run-up, don’t assume that you don’t have enough acclimatisation time to make it worthwhile. Every day will benefit you.

5. Recover right

Finally, make sure you do the right things to recover correctly. Rehydrate, with cool water if possible, but take on electrolytes and sodium as well. Make a particular effort to warm down gently, to stretch and to use a foam roller as heat and dehydration makes you more prone to cramps and muscle soreness. Try to get into the cool and shade as soon as possible and let your body temperature gradually return to normal.

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