Wearing a cap, thermoregulation, and thermal sensation during running in a hot environment.

AIM: The aim of this study was to determine if wearing a cap negatively alters thermoregulation or thermal sensation during prolonged running in the heat. METHODS: Nine well-trained runners ran for 1 hour at 67% VO(2)max in a hot environment (T(a) =31 degrees Celsius, RH=41%) wearing (CAP) or not wearing (NOCAP) a white cotton/polyester running cap. During both running trials, subjects consumed 2 mL x kg(-1) of cold water every 15 minutes. Thermal balance was assessed using rectal (T(re)) and skin temperatures (T(sk)) as well as measurement of whole-body sweat loss and thermal sensation of the head and of the overall body (8-point scale). RESULTS: There were no significant differences in T(re), T(sk) or whole-body sweat loss between conditions. When compared to NOCAP, forehead skin temperature increased more during CAP (P<0.05). Although there were no differences in ratings of thermal sensation of the overall body between treatments, ratings of thermal sensation of the head were higher (P<0.05) during CAP. There were no differences in heart rate or rating of perceived exertion between conditions. CONCLUSIONS. Despite higher ratings of thermal sensation of the head and higher forehead skin temperatures when wearing a cap during prolonged running in the heat, thermoregulation was not otherwise negatively altered.

Temperature of ingested water and thermoregulation during moderate-intensity exercise.

The effect of the temperature of ingested water on the rise in core temperature (Tco) during exercise is not clear. Seven trained subjects were recruited to complete 2 hr of recumbent cycling at 51% VO2peak in a temperate environment (Ta = 26 degrees C, relative humidity = 40%) on four occasions, while ingesting either no fluid (trial NF26), cold water (0.5 degree C; trial CD26), cool water (19 degrees C; trial CL26), or warm water (38 degrees C; trial WA26) during the second hour of exercise. A fifth trial was conducted during which convective and radiative heat loss were reduced by raising Ta to 31 degrees C. During this trial, subjects ingested cold water (0.5 degree C; trial CD31). When compared to WA26, over the second hour of exercise, CD26 attenuated the time-averaged changes in (Tco) and forearm blood flow and decreased whole-body sweat rate and forearm sweat rate (p < .05). Similarly, relative to WA26, the CL26 trial attenuated the time-averaged changes in Tco and reduced whole-body sweat rate (p < .05) during the second hour of exercise, but CL26 had no significant effect on forearm sweat rate or blood flow. Finally, regardless of beverage temperature, water ingestion (vs. NF26) reduced the time-averaged changes in Tco and in heat storage during the second hour of exercise (p < .05).

Metabolic responses when different forms of carbohydrate energy are consumed during cycling.

This study examined the effects of consuming the same amount of carbohydrate in solid form, liquid form, or both on metabolic responses during 2 hrs of cycling at 70% peak VO2 and on cycling time-trial performance. Subjects consumed 0.4 g carbohydrate/kg body mass before and every 30 min during exercise. The liquid was a 7% carbohydrate-electrolyte beverage and the solid was a sports bar (1171 kJ) in which 76%, 18%, and 6% of total energy was derived from carbohydrate, fat, and protein, respectively. Blood obtained at baseline, before exercise, and every 30 min was analyzed for glucose, insulin, lactate, hemoglobin, hematocrit, and plasma volume. There were no differences among the treatments for the blood parameters. Total carbohydrate oxidation and time-trial performance were also similar among treatments. Under thermoneutral conditions with equal liquid ingestion, the metabolic and performance responses are similar when consuming carbohydrate as a liquid, solid, or in combination during prolonged, moderate intensity cycling.

Insufficient dietary carbohydrate during training: does it impair athletic performance?

It is well established that adequate bodily carbohydrate reserves are required for optimal endurance. Based on this fact, it has been hypothesized that consumption of a diet with a high percentage of carbohydrate energy will optimize training adaptations and athletic performance. Scrutiny of the literature, however, does not strongly support the hypothesis that short-term or long-term reductions in dietary carbohydrate energy impairs training or athletic performance. Additional studies with well devised training protocols and performance tests are necessary to prove or disprove the hypothesis that a high carbohydrate energy diet is necessary to optimize training adaptations and performance. Because dietary carbohydrate contributes directly to bodily carbohydrate reserves, and because a high carbohydrate energy diet does not impair athletic performance, it remains prudent to advise athletes to consume a diet with a high carbohydrate energy content.