The spring marathon season is upon us. Some of us have already raced and others will do so in the coming weeks. As well-prepared as we might be for the main event, one thing that we have no control over is the weather. For runners whose training has taken place through the cold winter months, a sudden rise in temperature on race day can seriously affect your performance. We have just returned from taking part in an unseasonably warm Rotterdam marathon and estimate that we both ran 15-20 minutes slower than expected because of the heat.

The later in the season your marathon is, the more chance there is of the temperature rising. Last year’s VMLM was the hottest on record and we wrote here about the effect that this had on race times. We have also experienced higher than average  temperatures at recent editions of Milton Keynes, Edinburgh and Liverpool. European marathons are possibly even more likely to take place on hot, sunny days. We ran Mainz in early May 2018 in temperatures slightly hotter than London. High humidity can compound the problem.

The good news is that even with as little as two weeks left to go before your marathon date, after the main part of your training is over, there are still things that you can do to better prepare your body for a warm race day. Although everyone is different in how they cope with / respond to changes in environmental conditions, standard wisdom is that significant heat adaptation can take place by exercising at higher temperatures during this period.

Heat adaption enables us to:

Sweat more – The process of evaporation of sweat from the surface of the skin removes heat from the body. The more we sweat the more heat is removed.

Start sweating sooner – The sooner we start sweating the sooner we start to lose heat.

Reduce the sodium level in sweat – It is important that in sweating more we do not lose too much sodium. Having sufficient sodium in the body helps with water retention and prevents dehydration.

Increase plasma volume – Plasma is the colourless fluid component of the blood which transports blood cells around the body. An increased plasma volume ensures that more blood can flow to the skin (where it loses heat) without leaving working muscles short and thereby deprived of much-needed oxygen, which would result in fatigue.

Decrease in heart rate – An increase in blood volume also means that the heart does not have to work so hard to pump the blood around the body. In other words more plasma means a lower heart rate and improved blood flow.

All these changes make running in the heat less stressful to the body and reduce the chances of heat-related fatigue.

How to bring about heat adaptation

In an ideal world,  if you are about to run a marathon in a hotter climate the best solution would be to travel to your race destination two weeks before race day to acclimatise to the conditions there. However, this is not practical for most people and not relevant if the issue is a sudden rise in temperature on race day.

An alternative solution is to spend the two weeks before your race doing around an hour of moderate exercise a day in warm conditions. This could be in a warm gym or outside wearing more clothes than usual. Work up from light to moderate exercise over a few days. If it doesn’t fit with your taper it doesn’t all have to be running – try cycling or other forms of cross training.

Another suggestion is to take a hot bath or sauna after your normal training regime (20-30 mins or up to your own tolerance).

Dealing with the heat on race day

We’re sure you all know to wear light coloured, tech fabric clothes etc. There seems to be some disagreement as to whether caps help to shade the sun or just keep the heat in. Perhaps a visor is a better choice? The same goes for sun-cream. Some advice is that it prevents sweating so maybe choose your brand carefully. When you pour water over yourself to keep cool try to avoid your feet. We have learnt from past mistakes – wet feet on a hot day make you more vulnerable to blisters. Use body glide / Vaseline to prevent chaffing. Take in electrolytes in the liquid form or capsules.

Most importantly, reduce your expectations.  Take the increased temperature into account and reduce your pace from the start if necessary. It will probably lead to a quicker finish time overall – this is what we both failed to do in Rotterdam and we ended up having to take unplanned walk breaks. There is more disagreement on how much your pace will be affected by the heat. (Jeff Galloway suggests that over 60F/15C, runners are affected by approximately 2% for every 5F/3C increase.  This would mean a pace of 8min/mile at 15C would become become approximately 8:10min/mile at 65F/18C).

Do not let the heat discourage you. Reduce your pace and hopefully you will have a much more pleasant experience. We know how hard this is to do when you have trained with a targeted race time but let’s all try to keep it in mind.

It seems strange writing this post on what was a cool, if not cold, parkrun morning. A hot marathon seems so unlikely but keep an eye on the weather forecasts – it was just one hot day in Rotterdam and it could happen again.