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 [+ or -] 0.1 [degrees]C) induced no heat stress during a subsequent cycling bout (Kerr et al., 1998), and this was confirmed using a one-piece competition speed-suit (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 [+ or -] 0.1[degrees]C) for sub-2.5 hours of exercise (Kerr et al., 1998) or for sub-1 hour (i.e., 27.9 [+ or -] 0. 5[degrees]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 1. 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.
We contacted Guadeloupian triathlon clubs and recruited 19 tropically-acclimatized male volunteers, all internationally and regionally ranked and regularly competing in triathlons on the island. All competed in the 2012 Guadeloupe half Ironman triathlon in tropical conditions, i.e. with high ambient temperature and high relative humidity (27.2 [+ or -] 0.5[degrees]C; 80 [+ or -] 2%). The mean ([+ or -] SD) age, body mass, and height of the subjects were respectively 39.1 [+ or -] 6.9 yrs, 72.6 [+ or -] 7.9 kg, and 1.80 [+ or -] 0.07 m. Each athlete was contacted before the race and was sent a complete explanation of the study and an informed consent form. The day before the race, an interview was scheduled with each race entrant to ensure that each was fully informed of, and understood, the aims and methods of the study. All gave informed written consent to participate in the study. The Ethics Committee of the University of Guadeloupe approved the protocol. The race organizers also gave permission for the present investigation.
Half Ironman triathlon race description
The 2012 Guadeloupe half Ironman triathlon starting at 11 am consisted of two 0.95-km laps of swimming followed by 92 km of cycling and 21.1 km of running. The swimming phase consisted of a single 0.95-km double lap, the cycling phase consisted of three flat 30.6-km laps, and the half-marathon run consisted of three flat 7-km laps. Ambient temperature was 27.2 [+ or -] 0.5[degrees]C (range 26.528.2[degrees]C) and relative humidity was 80 [+ or -] 2% (78-82%). The cloud cover was minimal and no precipitation was recorded during the race. The ocean temperature was 29.5[degrees]C. Performance times for the swim, cycle, and run phases for all triathletes were retrieved from the race timing system.
Wet Bulb Globe Temperature (WBGT)
The WBGT index was recorded during the event with a QUESTemp[degrees] 32 Portable Monitor (QUEST Technologies, Oconomowoc, WI, USA). The mean WBGT over the competition duration for the 19 athletes was 25.2 [+ or -] 0.1[degrees]C (range 24.2-27.2), with the first subject finishing with a WBGT of 24.3 and the last with 24.2.
Recommendations, water intake and hydration
The athletes were permitted to eat and drink fluid ad libitum during the race. The water intake (WI) was the addition of the water ingested from the cycle phase and at refreshment. The subjects were asked to follow their usual diet and to refrain from alcohol and caffeine for 24 hr before the competition. At the end of the race, all athletes wrote down their WI between the start and end of the race. Urine samples were collected just before and immediately after the race and sent to the biochemistry laboratory of the University Hospital. Pre- and post-race urine osmolarity (Uosm) was measured to investigate changes in hydration status. We used a Uosm of >800 mOsm x [L.sup.-1] to indicate clinical dehydration, a cut-off which has been frequently used (Shirreffs and Maughan, 1998).
Temperature measurement and heart rate (HR)
Core temperature (TC) measurements were obtained throughout the race using the a CorTempTM 2000 ambulatory remote sensing system (HQ Inc., Palmetto, FL, USA) and pills that were given at least 6 hr before the race began, in line with previously reported guidelines (Byrne and Lim, 2007) (a telemetric check was performed to ensure that the temperature sensor was inside each volunteer and transmitting a signal). TC was measured just before the race (TC1), immediately after the swim phase in the transition tent while subjects were changing into their cycling attire (TC2), in the cycle-to-run transition tent while subjects were changing into their running attire (TC3), and immediately at the end of the half-marathon run (TC4). HR was recorded throughout the triathlon at 5-s increments using a chest band and wristwatch HR monitor (PolarVantage, Polar Electro Oy, Kempele, Finland).
Body height was determined before the race using a stadiometer (Tanita HR001, Tanita Europe B.V., Amsterdam, the Netherlands) to the nearest 0.01 m. Body mass (BM) was...