Effects of heat on running performance

In this blog we will analyse and break down the effect that climate (particularly temperature, humidity and radiation) can play on your distance running performance. Understanding how to choose an ideal race based on climate OR training to maximise your performance in a specific climate, can go a long way to determining whether or not you will run your goal time at your goal event. By the end of this blog, we hope you have an understanding as to how you much heat stress can affect your race day performance and how you can adjust your training to maximise performance and reduce risk.

Training Adaptations and Racing Considerations

Training in the heat can be very effective in helping you improve your racing results in both the heat and cold. Some key physiological adaptations that will occur with short term heat training exposure (minimum 6 runs in 2 weeks) is blood volume expansion via increased plasma volume as well as gains in optimal sweating/heat loss strategies. This can facilitate performance gains in the area of a few % (1-3%) even in cold or temperate environments. So be smart about your training in the summer (see our Front Runner guidelines further down) and see the gains at your next race!


Optimal Race Temperature

If you plan to travel for a race with the aim of running a PB, then climate needs to play a role in your selection (particularly for the Marathon). Numerous studies indicate that optimal Marathon running temperature is ~6 deg C for advanced recreational runners (3h) and down to ~3 deg C for elite runners (2h 10min). Elites require cooler conditions given they race at a higher percentage of their VO2 Max, meaning more aerobic metabolism and greater heat production at the cellular level.

If you do race in conditions hotter than this, what can you expect to happen to your performance? Thanks to research from Exercise Physiologist Matthew Ely and his team (2007), we know that elite Marathoners (2h 10min) racing in 10-15 deg C will add 1-2min (up to 1.5%) to their race time, whilst advanced Marathon runners (3h) racing in 10-15 deg C will add 4-8min (up to 4.2%), with time losses increasing as the race day temperature increases.

For those of you keen to investigate how much the heat may affect your individual performance, use the Jack Daniels calculator HERE by simply typing in your event, goal time and expected race day temperature.

Solar Radiation

 In addition to high temperatures and humidity, high levels of solar radiation have also been shown to negatively affect race day performance (Otani et al. 2016). If your race is likely to be in full sunlight (i.e. not early in the morning) then consider covering up some skin to reduce your skin temperature and prolong your time to exhaustion.

Travelling for Races

 The Perth climate is typically an ideal one for a distance runner, with training feasible the whole year round. One issue that many Australian cities will face is a significant difference between Summer and Winter training temperatures. In Perth, it is common to have to train in >30 deg heat at 5.30pm through the summer, compared <10 deg at the same time in Winter. Whilst the physiology at the cellular level will be similar, the body’s need to cool itself down (primarily through redirecting blood flow to the skin) is completely different. So how your body will deal with heat stress on race day will be completely different if you have trained through the Summer or Winter. Two great examples we see each year are the Busselton and Perth Running Festivals. The Busselton Fun Run (early February) is an example of the ideal situation. Training through the Perth Summer presents the body with regular heat stress and allows for significant adaptation in blood plasma volume. However, driving south to a cooler climate to race (<15 deg), allows this extra blood to be directed to the working muscles, effectively increasing their ability to use oxygen as the heat stress is not there. It is therefore very common to see big PB runs from runners who have entered the event with a consistent training block. The Tokyo Marathon in February is another great example of training in the heat and racing in the cool (<5 deg C) to facilitate optimal results.

On the flip side, the Perth Marathon highlights the risks of training in the cold and racing in the heat. Raced in October, training is done through the Winter in conditions far cooler than race day, meaning that the body is not exposed to the regular heat stress required to gain the necessary adaptations to perform optimally on race day in a warm and sometimes hot climate.

In these two instances, the race day temperature (~15-20deg) is often the same, but performance is often significantly different due to the average training temperature in the lead up to the race. So if you are travelling for a race, make sure you investigate the likely race day climate and assess the potential disparity of your training conditions vs. race conditions.








Front Runner Guidelines for Training in the Perth Summer

At Front Runner, we often reference the three pillars of successful distance runners; training volume (high), anaerobic threshold (high) and training days missed (low). Hot weather certainly makes achieving the last pillar more difficult, however aiming to miss as few days of scheduled training as possible will ensure you are in the best position to achieve your short and long term goals. So if some hot conditions are forecast, what can you do training wise (hydration and nutritional strategies are also crucial here – READ MORE) to ensure you maximise your training adaptations, but lower your risk of overdoing it and missing subsequent training sessions?

A key point to make first off is that heat training is all relative. If you’re used to regularly training in hot conditions (defined as >34 deg C & >55% humidity), then these conditions will have a minimal effect on your training session. However, if you have rarely, if ever, trained in warm conditions, then the heat will have a more significant effect on your training. So the further away from the median temperature you would normally train at, the more conservative you need to be with your training.

High Intensity Training

If you are planning on completing a training session that is on OR above your anaerobic threshold (see HERE), then we recommend you aim to complete the usual volume you would spend at your threshold (e.g. 20-25min), but make sure you reduce the intensity (pace) of the workout. As you approach your threshold pace, your body is sitting on a fine line as to whether this intensity is sustainable for more than a few minutes. So with the added heat stress, your body now has a trade-off as to whether it sends blood to your skin to assist in cooling, or to keep sending blood to the working muscles to supply oxygen. So to avoid exceeding your threshold too early in a training session and compromising the volume of the session, we recommend dropping your threshold pace by a minimum of 5-8s per km (for runners who regularly train in the heat) or up to 10-12s per km (for those who rarely training in the heat). This will allow you to have an oxygen reserve that you can gradually eat into as the workout progresses.

Low Intensity Training

If you are planning on completing an easy, steady or long run (see HERE) in hot conditions, then we begin to look at reducing the planned volume (duration) of the run. These runs can naturally have a larger variation in the intensity (pace) at which they are completed, so ensure you stay on the conservative side of the pace spectrum (i.e. long running closer to your recovery pace vs. your steady pace) when completing them in hot conditions. If you run on your steady pace (correlating with your aerobic threshold), then the blood flow trade off between the skin and working muscles means the associated exertion to run steady is more likely to be a tempo effort. Whist it may feel ok at the time (given you are still below your anaerobic threshold), this can be enough to induce extra stress during a training run that should not stress the body significantly. This can then create a domino effect where subsequent sessions later in the week are affected and overall training quality and quantity is lowered.

When looking at reducing your run volume, beginner to recreational runners should be cautious about running for >1h in hot conditions (remember that hot is a relative term compared to what you usually training in), whilst advanced runners should be cautious about running for >1h 30min. If you are in a building phase of your training (i.e. your goal event is still a while away), then we highly recommend sticking to these volume limits. Cutting a long run or easy run marginally short and respecting the conditions will ensure you don’t over stress your body and end up missing whole sessions down the track. If you are into a specific phase of your training (i.e. your goal race in less than 3-4 weeks away) and the run is a race-specific preparation run, then you are best not to tinker with the run. Aim to complete it as planned on a later date when the conditions are more favourable (the specifics of which should be discussed with your coach). This allows the specific aims of the session to be achieved and to give you the necessary information to strategically plan for your goal race.



We trust you now have a greater understanding as to how you can ensure your race selection provides you with the best opportunity to beat your best as well as how you can adjust your training when faced with an increased relative training temperature. If you wish to know more about this topic, or anything to do with your running training, please get in touch with our expert coaching team who are ready to assist you towards your next running goal! Please email coach@frontrunnersports.com.au or see our website: www.frontrunnersports.com.au

Book a meeting and get started to your goals with an accredited Front Runner coach HERE

Running Regards,

Team Front Runner