Blood Glucose Responses to Carbohydrate Feeding Prior to Exercise in the Heat: Effects of Hypohydration and Rehydration

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Marcos Echegaray
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Lawrence E. Armstrong
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Carl M. Maresh
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Deborah Riebe
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Robert W. Kenefick
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John W. Castellani
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Stavros Kavouras
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Douglas Casa
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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 · kg−1 · min−1) exercised at 50% V̇O2maxin a 33 °C environment until a 4% body weight loss was achieved. Following this, subjects were rehydrated (25 ml · kg−1) with either: 0.45% IV saline (45IV), 0.9% IV saline (9IV), or no fluid (NF). Subjects then ingested 1 g · kg−1 of carbohydrate and underwent an exercise test (treadmill walking, 50% V̇O2max, 36 °C) for up to 90 min. Compared to pre-exercise level (294 mg · dl−1), PG increased significantly (>124 mg · 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 μIU · ml−1) no significant differences between trials were observed. Peak plasma norepinephrine was significantly higher in NF (640 ± 66 pg · ml−1) compared to the 45IV and 9IV trials (472 ± 55 and 474 ± 52 pg · 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.

M. Echegaray, L.E. Armstrong, and CM. Maresh are with the Department of Physiology & Neurobiology at The University of Connecticut, Storrs, CT 06269. Additionally, Armstrong and Maresh along with D. Riebe, R.W. Kenefick, J.W. Castellani, S. Kavouras, and D. Casa are with the Department of Kinesiology at The University of Connecticut. M. Echegaray is now with the Department of Biology at the University of Puerto Rico.

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