Hydration and Thermoregulation During a Half-Ironman Performed in Tropical Climate

The aim of this study was to compare the core temperature (TC) and markers of hydration status in athletes performing a half Ironman triathlon race in hot and humid conditions (27.2 ± 0.5°C, relative humidity was 80 ± 2%). Before and immediately after the 2012 Guadeloupe half Ironman triathlon, body mass and urine osmolarity (mean ± SD) were measured in 19 well-trained male triathletes. TC was measured before and after the race, and at each transition during the event, using an ingestible pill telemetry system. Ambient temperature and heart rate (HR) were measured throughout the race. Mean ± SD performance time was 331 ± 36 minutes and HR was 147 ± 16 beats·min-1. Wet bulb globe temperature (WBGT) averaged 25.4 ± 1.0°C and ocean temperature was 29.5°C. The average TC at the beginning of the race (TC1) was 37.1 ± 0.7°C; it was 37.8 ± 0.9°C after swimming (TC2), 37.8 ± 1.0°C after cycling (TC3), and (TC4) 38.4 ± 0.7°C after running. Body mass significantly declined during the race by 3.7 ± 1.9 kg (4.8 ± 2.4%; p < 0.05), whereas urine osmolarity significantly increased from 491.6 ± 300.6 to 557.9 ± 207.9 mosm·L-1 (p < 0.05). Changes in body mass were not related to finishing TC or urine osmolarity. Ad libitum fluid intake appears applicable to athletes acclimatized to tropical climate, when performing a half Ironman triathlon in a warm and humid environment. Key points Ad libitum fluid intake appears applicable to athletes acclimatized to tropical climate when performing a half Ironman triathlon in a warm and humid environment. The final core temperature average was 38.8 ± 0.7oC after the event in these triathletes and the athletes showed no evidence of heat illness while competing in a warm and humid environment. Core temperature was dependent on both activity and anthropometry. Key words: Aerobic exercise, triathlon, hygrometry, hydration Introduction Cyclic aerobic exercise is negatively affected by a hot environment; this has been demonstrated for running (Maughan, 2010) and cycling, although in cycling, it depends on somewhat on the type of race (Nybo, 2010). Swimming in hot water or a tropical climate has also been shown to stimulate and induce thermoregulatory adaptations and to impair performance (Hue and Galy, 2012). The effects of various factors on triathlon thermoregulation, dehydration and performance have been widely explored. For example, one study found that wearing a wet suit while swimming in relatively warm water as defined by Kerr (25.4 ± 0.1 °C) induced no heat stress during a subsequent cycling bout (Kerr et al., 1998), and this was confirmed using a one-piece competition speedsuit (Peeling and Landers, 2007). Moreover, no hyperthermia- or dehydration-induced thermoregulatory failure has been demonstrated during long-distance (i.e., Ironman) triathlons (Laursen et al., 2006) (Sharwood et al., 2004). However, the studies in hot and humid conditions/climate were performed in a laboratory in relatively warm water (i.e., 25.4 ± 0.1°C) for sub-2.5 hours of exercise (Kerr et al., 1998) or for sub-1 hour (i.e., 27.9 ± 0.5°C) (Peeling and Landers, 2007). The half Ironman triathlon (i.e., 1.9-km swimming, 90-km cycling and 21.1-km running) has become very popular but little has been studied for endurance events i.e. >3h in duration, especially in a tropical climate. Thus, our understanding of the influences of a warm and humid environment and fluid intake strategies on aerobic exercise capacity has essentially been studied through experiments conducted on cyclists or runners within the confines of a laboratory. In fact, only one study examined the relationship between warm and humid conditions and Ironman triathlon exercise capacity (Sharwood et al., 2004). These authors reported that the large changes in body weight during the triathlon were not associated with higher rectal temperatures post-race. Although the negative effects of hot-wet conditions (i.e., the so-called tropical climate) have been demonstrated for almost every cyclic sport (Gonzalez-Alonso et al., 2008), such as swimming (Wade and Veghte, 1977), cycling (Voltaire et al., 2003) and running (Kenefick et al., 2007), no study to our knowledge has explored the thermoregulatory and hydration responses to a relatively long-distance triathlon (i.e., the half Ironman) performed in tropical conditions. We therefore tested the hypothesis that the swimming phase performed in warm temperature under high radiation would induce relative hyperthermia that would not be reversed during the cycling phase and would be aggravated during running.