Blood glucose responses to carbohydrate feeding prior to exercise in the heat: effects of hypohydration and rehydration.
This study assessed the plasma glucose (PG) and hormonal responses to carbohydrate ingestion, prior to exercise in the heat, in a hypohydrated state versus partial rehydration with intravenous solutions. On separate days, 8 subjects (21.0 +/- 1.8 years; 57.3 +/- 3.7 ml x kg(-1) x min(-1)) exercised at 50% VO2max in a 33 degree C environment until a 4% body weight loss was achieved. Following this, subjects were rehydrated (25 ml x kg(-1)) with either: 0.45% IV saline (45IV), 0.9% IV saline (9IV), or no fluid (NF). Subjects then ingested 1 g x kg(-1) of carbohydrate and underwent an exercise test (treadmill walking, 50% VO2max, 36 degrees C) for up to 90 min. Compared to pre-exercise level (294 mg x dl(-1)), PG increased significantly (>124 mg x dl(-1)) at 15 min of the exercise test in all trials and remained significantly elevated for 75 min in NF, 30 min more than in the 2 rehydration trials. Although serum Insulin increased significantly at 15 min of exercise in the 45IV trial (7.2 +/- 1.2 vs. 23.7 +/- 4.7 mIU x ml(-1)), no significant differences between trials were observed. Peak plasma norepinephrine was significantly higher in NF (640 +/- 66 pg x ml(-1)) compared to the 45IV and 9IV trials (472 +/- 55 and 474 +/- 52 pg x ml(-1), respectively). In conclusion, ingestion of a small solid carbohydrate load prior to exercise in the 4% hypohydration level resulted in prolonged high PG concentration compared to partial IV rehydration.
Department of Physiology & Neurobiology, The University of Connecticut, Storrs, CT 06269, USA.
M
M
Echegaray
L E
LE
Armstrong
C M
CM
Maresh
D
D
Riebe
R W
RW
Kenefick
J W
JW
Castellani
S
S
Kavouras
D
D
Casa
D000328:Adult; D001786:Blood Glucose / Q000032:analysis*; D003681:Dehydration / Q000097:blood / Q000503:physiopathology*; D004040:Dietary Carbohydrates / Q000008:administration & dosage* / Q000494:pharmacology; D004837:Epinephrine / Q000097:blood; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006358:Hot Temperature; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D009638:Norepinephrine / Q000097:blood; D009994:Osmolar Concentration; D015532:Rehydration Solutions
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D007328:Insulin; D015532:Rehydration Solutions; D009638:Norepinephrine; D004837:Epinephrine