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INTRODUCTION

Nutrition intervention can be complex when athletes train and compete in unique environmental conditions. High altitude and extreme temperatures induce substantial changes in performance capacity and alter the usual response to exercise, which influences nutrition recommendations. The fuel for exercise in harsh environmental conditions is influenced by an athlete’s fitness, tolerance to fluid and food, and the unique demands of the sport. The effects of high altitude, cold and heat are usually better tolerated in short-duration events than in prolonged endurance events. This chapter reviews the evidence that informs nutrition recommendations for athletes who are training and competing at altitude and at extreme environmental temperatures.

Background

Altitude and heat impair performance in endurance events (Nybo et al. 2014; Saunders et al. 2019). A consensus statement by the Medical Commission of the International Olympic Committee addresses the risks associated with exercise in hot, cold and hypoxic conditions (Bergeron et al. 2012). Although the influence of acute cold conditions on sporting performance is not as profound as altitude and heat, prolonged training in cold temperatures can induce physiological adaptations. This chapter complements reviews addressing the nutrition implications of training and competing at altitude (Stellingwerf et al. 2019), in cold (Meyer et al. 2011) and in heat (McCubbin et al. 2020).

Physiological stress response to altitude, cold and heat

Elevated catecholamines, reflective of increased sympathetic activity, have been reported during rest and exercise at altitude (Mazzeo et al. 1995), in the heat (Febbraio 2001) and in cold conditions (Shephard 1993). Resting metabolic rate (RMR) can increase following exposure to hypoxia, cold and heat. Similarly, fluid loss tends to be greater at rest and during exercise in environmental extremes. An increase in sweat rate during submaximal exercise in the heat is a perfect example of a unique physiological response that drives fluid loss (McCubbin et al. 2020). Elevated sympathetic activity increases reliance on carbohydrate (CHO) metabolism. These effects are especially evident at altitude and in the heat (Febbraio et al. 1996; Katayama et al. 2010). Disrupted sleep following exercise at altitude, in cold conditions and the heat may also occur and impairs recovery (Buguet et al. 2007). In extreme environmental conditions, athletes may initially experience a greater perceived exertion for a given workload and reduction in exercise capacity, compared to sea level. Over time, the athlete training in these environments will adapt physiologically and, with appropriate nutrition and recovery, become acclimatised.

ALTITUDE PHYSIOLOGY

A decrease in barometric pressure at altitude reduces oxygen availability. Altitude is categorised as low (1000–2000 m), moderate (2000–3000 m), high (3000–5000 m) and extreme (>5000 m) (Levine & Stray-Gundersen 2002). To provide oxygen to metabolically active tissue, the physiological response to ...

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