Heat acclimation in preparation for the Marathon des Sables

Research at the Environmental Extremes Lab at the University of Brighton has been supporting athletes competing in the Marathon des Sables race since 2006. The lab continues to work with and learn from competitors in the annual race. 

Multi-stage, ultra-endurance events within extreme environmental conditions are becoming increasingly popular with endurance athletes. Deemed the ‘toughest foot race on earth’ the Marathon des Sables (MdS), is a ~250 km multi-day race across the Sahara Desert in Morocco, which attracts around 1000 competitors annually from around the world. During the MdS race, competitors are self-dependent, carrying their own backpacks which weigh around 5-10 kg in extreme levels of heat stress (~40°C). The route covers sand dunes, dry river beds, stony and rocky surfaces, and is relentless in terms of physical and mental fatigue.

The athletes face numerous physiological challenges including; cumulative fatigue, restricted water and food availability, sleep deprivation, high solar heat loads with limited shade and, prolonged metabolic heat production. Such consequences exacerbate physiological strain, and increase the likelihood of dehydration, skin tissue injuries and risk of exertional heat-related illnesses (EHRI). These are obviously detrimental to health, which can lead to race-withdrawal and serious health consequences. It is therefore, imperative that athletes prepare effectively through heat acclimation (HA), which includes repeated, prolonged exercise exposures to high temperatures (>30°C) and moderate-high humidity (>40 per cent). Short-term HA (STHA) can induce nearly 75 per cent of physiological adaptations which includes a reduction in heart rate and core temperature, in addition to lowered perceived exertion, along with improved thermal comfort, sensation and perceived fatigue.

At the University of Brighton, we have been exploring the methods and mechanisms around optimising heat acclimation since 2004 when we first supported one of our own BSc (Hons) Sport and Exercise Science students in their heat acclimation strategy ahead of completing, and the being the first British runner to finish, the MdS. During this extended time period, research from the Environmental Extremes Laboratory (EEL) has contributed significantly to the international body of literature around phenotypic adaptations to repeated heat exposures. Our work has contributed to the research of six PhD students, been presented at national and international conferences, received recognition through several international awards and members from EEL contributed to the 2017 British Association of Sport and Exercise Sciences (BASES) Expert Statement: Interventions for Improving Performance in the Heat. We have published nearly twenty research studies around heat acclimation in peer-reviewed journals, led symposia and been invited speakers internationally on the subject. Consequently, the methods prescribed and measures taken during our delivery of heat acclimation strategies to MdS runners and other athletes competing in major events under heat stress, are all research-informed.

In our specific research study investigating the physiological, perceptual and immunological responses to short-term heat acclimation (STHA) prior to a MdS (Willmott et al 2016), athletes visited the laboratories four to six times for controlled hyperthermia heat acclimation sessions (60 minutes per day), which included running and cycling in 45°C and 30 per cent relative humidity in the lead up to their departure for Morocco. Pre, during and post sessions, physiological and perceptual measures were recorded. Immunological measures were recorded pre-post sessions one and four.

Physiological and psychological responses

Over the course of the heat acclimation we observed hallmark heat adaptations in physiological and perceptual responses during exercise in heat stress, in particular a 14 per cent greater sweat rate that helps promote effective heat loss. No changes were found in white blood cell counts or content. Therefore, four days of STHA facilitates effective perceptual adaptations, without compromising immune status prior to an ultra-endurance race in heat stress. A greater physiological strain may be required to confer optimal physiological adaptations.

Race impact

In 2016, nine out of 10 athletes we supported completed the race safely and successfully, with some even finishing in the top 10 per cent of the field. Some of the feedback from the athletes included, the improvement in mental toughness and confidence gained through training in their teams in the extreme heat of our chamber, while others felt that learning about their heat rate, sweat rate and hydration guidelines really helped them during the race and how to pace themselves during the peak temperatures.

In 2017, nine out of 10 runners we worked with completed all the stages of the competition and six were within the top 20 per cent of the 1300 competitors.

Elisabet Barnes, who Ash Willmott works closely with, was the first female across the finishing line for the second time in three years.

Research paper

Willmott, A., Hayes, M., Waldock, K., Relf, R., Watkins, E., James, C., Gibson, O., Smeeton, N., Richardson, A., Watt, P., Maxwell, N. (2016) Short-term heat acclimation prior to a multi-day desert ultra-marathon improves physiological and psychological responses without compromising immune status. Journal of Sports Sciences. DOI:10.1080/02640414.2016.1265142