Core temperature and metabolic responses after carbohydrate intake during exercise at 30 degrees C.
BACKGROUND
Carbohydrate ingestion has recently been associated with elevated core temperature during exercise in the heat when testing for ergogenic effects. Whether the association holds when metabolic rate is controlled is unclear. Such an effect would have undesirable consequences for the safety of the athlete.


OBJECTIVE
To examine whether ingesting fluids containing carbohydrate contributed to an accelerated rise in core temperature and greater overall body heat production during 1 hour of exercise at 30 degrees C when the effort was maintained at steady state.


METHODS
Crossover design (repeated measures) in randomized order of treatments of drinking fluids with carbohydrate and electrolytes (CHO) or flavored-water placebo with electrolytes (PLA). The beverages were identical except for the carbohydrate content: CHO = 93.7 +/- 11.2 g, PLA = 0 g.


METHODS
Research laboratory.


METHODS
Nine physically fit, endurance-trained adult males.


METHODS
Using rectal temperature sensors, we measured core temperature during 30 minutes of rest and 60 minutes of exercise at 65% of maximal oxygen uptake (Vo(2) max) in the heat (30.6 degrees C, 51.8% relative humidity). Participants drank equal volumes (1.6 L) of 2 beverages in aliquots 30 minutes before and every 15 minutes during exercise. Volumes were fixed to approximate sweat rates and minimize dehydration.


METHODS
Rectal temperature and metabolic response (Vo(2), heart rate).


RESULTS
Peak temperature, rate of temperature increase, and metabolic responses did not differ between beverage treatments. Initial hydration status, sweat rate, and fluid replacement were also not different between trials, as planned.


CONCLUSIONS
Ingestion of carbohydrate in fluid volumes that minimized dehydration during 1 hour of steady-state exercise at 30 degrees C did not elicit an increase in metabolic rate or core temperature.
Horswill
Craig A
CA
Gatorade Sports Science Institute, Barrington, IL 60010, USA. craig.horswill@gatorade.com
Stofan
John R
JR
Lovett
Shannon C
SC
Hannasch
Chris
C
D000328:Adult; D001831:Body Temperature / Q000502:physiology*; D001833:Body Temperature Regulation; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000378:metabolism*; D004573:Electrolytes / Q000378:metabolism*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005440:Fluid Therapy; D005632:Fructose / Q000008:administration & dosage / Q000378:metabolism; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism; D006305:Health Status Indicators; D006339:Heart Rate; D018882:Heat Stress Disorders / Q000209:etiology*; D006801:Humans; D008297:Male
D004040:Dietary Carbohydrates; D004573:Electrolytes; D005632:Fructose; D005947:Glucose