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Run Hot or Run Cold? What Science Reveals

One of the reasons behind the steady improvement in endurance running times around the world has been the close interaction between sports science, and athletes and coaches. In the past, some scientists have been very comfortable wearing their white coats whilst confined to their laboratories, seldom getting out into the “real world” to engage with athletes and coaches. This is great for publishing academic papers and extending our theoretical knowledge of how the body works, but at times has made little contribution to the genuine enhancement of human performance. This is not deliberate, and often stems from a lack of communication between the scientists, and the coaches and athletes. Scientists have the knowledge, but communicating it in a manner that coaches and athletes can understand and use has frequently been the challenge.

I have always been a strong advocate of the need to break down that communication barrier, and it helps that many successful sports scientists are also runners (albeit not at the same level as many Olympians!). This means that they understand what areas runners want to understand better, and know how to communicate the findings of their studies to runners in a manner than can help to achieve the small but significant gains that are so critical at all levels.

Excellent Example of Scientific Study in Sport 

A great example of this is a scientific study in the UK that was funded by the Cancer Research UK London Winter Run, the highly popular 10k race that is held around the streets of London in February. Using the state-of-the-art environmental chamber at St Mary’s University in London – the home of many great runners including Mo Farah - the average climatic conditions in London in February were replicated, and then compared them with those experienced during the hotter months of the UK summer.

Once the team of scientists had turned up the heat for the summer, and turned it down for the winter, they asked a group of mixed ability runners to run for 40 minutes twice, once at a temperature of 22 degrees Celsius, and then again, a week later, at a temperature of 8 degrees Celsius. The running speed was fixed at a pace equivalent to 80% of their maximum oxygen uptake, which was calculated after a series of preliminary tests in the St Mary’s sports science laboratory. 80% of maximum was chosen since research studies have shown that this is typical of the percentage of maximum that most athletes can sustain during a 10k.

Before each run, the runners’ body weight was measured, and during the runs their heart rate, oxygen uptake, and their perception (or feelings) of effort and “thermal stress” were also measured. After each runner had been assessed under both the hot and cold conditions, the data were collated and analysed to see what statistical differences, if any, were apparent.

Study Results 

Once the statistical analysis had been completed, the St Mary’s team found that without exception, the runners were better able to cope (both physiologically and psychologically) with running in the cooler “winter” conditions when compared with the hotter “summer” conditions. The data showed that on average, their heart rates were 6% lower in the cooler conditions, whilst their (each runner lost an average of 1.3 litres of fluid when running for 40 minutes in the warm conditions). Despite the running speeds being the same under both conditions, in the cool the runners’ perception of effort, and thermal stress, was around 32% lower, confirming that the physiological differences translated into a genuine feeling that running is easier when conditions are cool.

Run Hot or Cold?

In the darker colder days of winter, when it is sometimes a hard struggle to find the motivation to train and race, these findings are a real encouragement to put on your training shoes, a high visibility running top, and get running. Most of us will train according to how we feel – if a run feels tough, we tend to slow down, but if we feel good, we are more likely to speed up. The findings of this study suggest that training in colder conditions is more likely to result in a better training session, and the ability to train at a higher intensity when compared with training in warm conditions. As we know from many other studies, higher intensity training places additional physiological overload on the body, and can lead to significant positive adaptations to the muscles and cardio-vascular system, which in turn result in improved performances.

But cooler conditions are not only conducive to better training runs, they are also more likely to produce better racing conditions and times. Whilst we all like to feel some warmth and sun on our skin, this places additional challenges on the body’s ability to keep cool, and to lose the heat generated when running. As a result we sweat and dehydrate more in the warmth, and the heart has to beat more rapidly to pump blood to the skin so that heat can be lost. Cooler conditions make this vital physiological process of “thermoregulation” easier, and allow body heat to be lost in a more efficient manner. As a result, runners can race at a higher intensity and pace and consequently stand a much better chance of obtaining faster - or even personal best - times.

Winter Conditions? Better Performance.  

What does this mean for coaches and athletes? Well it is clear that we have shifts in the climate between the winter and summer months, and even in countries where these differences are not extreme, they still present runners with different physiological and thermoregulatory challenges. Although traditionally many runners will focus on 10k’s during the summer, it does seem as if the intensity of both training for, and racing, 10k’s is such that the cooler winter conditions are more preferable to better performances. So as we all enter the winter months, do not despair. Our research has shown that performances at all levels can improve, and this is the time to optimise returns from training and racing.

When science and the findings from research studies are applied properly, it really can make a meaningful difference regardless of a runner’s level of ability. Scientists will continue to gain deeper and better insights into the demands of running, and, crucially, disseminate their findings in a way that can benefit everyone, whether a novice or an international athlete.


Author: Dr. Brewer

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