influence of low versus high carbohydrate diet on a 45-min strenuous cycling exercise

• Published in: International journal of sport nutrition and exercise metabolism 2004-02, Vol.14 (1), p.62-72
• Main Authors: Kavouras, S.A, Troup, J.P, Berning, J.R
• Format: Article
• Language: English
• Subjects: Adult; bicycling; Bicycling - physiology; Biopsy; Blood Glucose - metabolism; carbohydrate loading; Cross-Over Studies; Dietary Carbohydrates - administration & dosage; Dietary Carbohydrates - metabolism; exercise; free fatty acids; glucose; glycogen; Glycogen - metabolism; glycogenolysis; Heart Rate - drug effects; Heart Rate - physiology; high carbohydrate diet; Humans; low carbohydrate diet; Male; men; Muscle, Skeletal - metabolism; Oxygen Consumption; Pulmonary Gas Exchange; strength training
• ISSN: 1526-484X; 1543-2742
• DOI: 10.1123/ijsnem.14.1.62

To examine the effects of a 3-day high carbohydrate (H-CHO) and low carbohydrate (L-CHO) diet on 45 min of cycling exercise, 12 endurance-trained cyclists performed a 45-min cycling exercise at 82 ± 2% VO(2peak) following an overnight fast, after a 6-day diet and exercise control. The 7-day protocol was repeated under 2 randomly assigned dietary trials H-CHO and L-CHO. On days 1-3, subjects consumed a mixed diet for both trials and for days 4-6 consumed isocaloric diets that contained either 600 g or 100 g of carbohydrates, for the H-CHO and the L-CHO trials, respectively. Muscle biopsy samples, taken from the vastus lateralis prior to the beginning of the 45-min cycling test, indicated that muscle glycogen levels were significantly higher (p < .05) for the H-CHO trial (104.5 ± 9.4 mmol/kg wet wt) when compared to the L-CHO trial (72.2 ± 5.6 mmol/kg wet wt). Heart rate, ratings of perceived exertion, oxygen uptake, and respiratory quotient during exercise were not significantly different between the 2 trials. Serum glucose during exercise for the H-CHO trial significantly increased (p < .05) from 4.5 ± 0.1 mmol · L-1 (pre) to 6.7 ± 0.6 mmol · L-1 (post), while no changes were found for the L-CHO trial. In addition, post-exercise serum glucose was significantly greater (p < .05) for the H-CHO trial when compared to the L-CHO trial (H-CHO, 6.7 ± 0.6 mmol · L-1; L-CHO, 5.2 ± 0.2 mmol · L-1). No significant changes were observed in serum free fatty acid, triglycerides, or insulin concentration in either trial. The findings suggest that L-CHO had no major effect on 45-min cycling exercise that was not observed with H-CHO when the total energy intake was adequate.