Hyperthermia during Olympic triathlon: influence of body heat storage during the swimming stage.

The purpose of this project was to determine whether mild heat stress induced by wearing a wet suit while swimming in relatively warm water (25.4 +/- 0.1 degrees C) increases the risk of heat injury during the cycling and running stages of an International distance triathlon in a hot and humid environment (32 degrees C and 65% RH). Five male triathletes randomly completed two simulated triathlons (swim = 30 min; bike = 40 km; run = 10 km) in the laboratory using a swimming flume, cycle ergometer, and running treadmill. In both trials, all conditions were identical, except for the swimming portion in which a neoprene wet suit was worn during one trial (WS) and a swimming suit during the other (SS). The swim portion consisted of a 30-min standardized swim in which oxygen consumption (VO2) was replicated, regardless of WS or SS. During the cycling and running stages, however, the subjects were asked to complete the distances as fast as possible. Core temperature (Tc) was not significantly different between the SS and WS trials at any time point during the triathlon. However, mean skin temperature (Tsk) and mean body temperature (Tb) were higher (P < 0.05) in the WS at 15 (Tsk = +4.1 degrees C, Tb = +1.5 degrees C) and 30 min (Tsk = +4 degrees C, Tb = +1.6 degrees C) of the swim. These Tsk and Tb differences were eliminated by 15 min of the cycling stage and remained similar (P > 0.05) through the end of the triathlon. Moreover, there were no differences (P > 0.05) in VO2, heart rate (HR), rating of perceived exertion (RPE), or thermal sensation (TS) between the WS and SS. Additionally, no significant differences were found in cycling (SS = 1:14:46 +/- 2:48 vs WS = 1:14:37 +/- 2:54 min), running (SS = 55:40 +/- 1:49 vs WS = 57:20 +/- 4:00 min), or total triathlon times (SS = 2:40:26 +/- 1:58 vs WS = 2:41:57 +/- 1:37 min). These data indicate that wearing a wet suit during the swimming stage of an international distance triathlon in 25.4 degrees C water does not adversely affect the thermoregulatory responses of the triathlete on the subsequent cycling and running stages.

Thermoregulatory responses to cycling with and without a helmet.

This study examined the effects of wearing a helmet on selected body temperatures and perceived heat sensation of the head and body while cycling in a hot-dry (D) (35 degrees C, 20% relative humidity (RH) and hot-humid (H) (35 degrees C, 70% RH) environment. Ten male and four female cyclists (mean +/- SD: males = age 27 +/- 7 yr, peak O2 uptake (VO2) 4.10 +/- 0.54 L.min-1; females = age 26 +/- 3 yr, peak O2 uptake (VO2) 3.08 +/- 0.49 L.min-1) performed four randomized 90-min cycling trials at 60% of peak VO2 both with (HE) and without (NH) a commercially available cycling helmet in both D and H environments. VO2, core (Te), skin (Tsk), and head skin temperatures, heart rate (HR), rating of perceived exertion (RPE), and perceived thermal sensation of head (TSH) and body (TSB) were measured throughout exercise. For all measured variables, no significant difference was evident between HE and NH. However, Tc, Tsk, and mean head skin temperatures were higher (P < 0.001) in H than D. Likewise, RPE, TSH, TSB (P < 0.001), and sweat rates (H = 1.33 +/- 0.32, D = 1.14 +/- 0.23 L.h-1) (P < 0.01) were higher in H versus D. Results indicate that use of a commercially available cycling helmet while riding in a hot-dry or hot-humid environment does not cause the subjects to become more hyperthermic or increase perceived heat sensation of the head or body.

Effects of diet on muscle triglyceride and endurance performance.

The purpose of this investigation was to examine the effects of diet on muscle triglyceride and endurance performance. Seven endurance-trained men completed a 120-min cycling bout at 65% of maximal oxygen uptake. Each subject then ingested an isocaloric high-carbohydrate (Hi-CHO; 83% of energy) or a high-fat (Hi-Fat; 68% of energy) diet for the ensuing 12 h. After a 12-h overnight fast, a 1,600-kJ self-paced cycling bout was completed. Muscle triglyceride measured before (33.0 +/- 2.3 vs. 37.0 +/- 2.1 mmol/kg dry wt) and after (30.9 +/- 2.4 vs. 32.8 +/- 1.6 mmol/kg dry wt) the 120-min cycling bout was not different between the Hi-CHO and Hi-Fat trials, respectively. After the 24-h dietary-fasting period, muscle triglyceride was significantly higher for the Hi-Fat (44.7 +/- 2.4 mmol/kg dry wt) vs. the Hi-CHO (27.5 +/- 2.1 mmol/kg dry wt) trial. Furthermore, self-paced cycling time was significantly greater for the Hi-Fat (139.3 +/- 7.1 min) compared with the Hi-CHO (117.1 +/- 3.2 min) trial. These data demonstrate that there was not a significant difference in muscle triglyceride concentration before and after a prolonged moderate-intensity cycling bout. Nevertheless, a high-fat diet increased muscle triglyceride concentration and reduced self-paced cycling performance 24 h after the exercise compared with a high-carbohydrate diet.