Effect of low- and high-glycemic-index meals on metabolism and performance during high-intensity, intermittent exercise.
Consuming carbohydrate-rich meals before continuous endurance exercise improves performance, yet few studies have evaluated the ideal preexercise meal for high-intensity intermittent exercise, which is characteristic of many team sports. The authors' purpose was to investigate the effects of low- and high-glycemic-index (GI) meals on metabolism and performance during high-intensity, intermittent exercise. Sixteen male participants completed three 90-min high-intensity intermittent running trials in a single-blinded random order, separated by ~7 d, while fasted (control) and 2 hr after ingesting an isoenergetic low-GI (lentil), or high-GI (potato and egg white) preexercise meal. Serum free fatty acids were higher and insulin lower throughout exercise in the fasted condition (p < .05), but there were no differences in blood glucose during exercise between conditions. Distance covered on a repeated-sprint test at the end of exercise was significantly greater in the low-GI and high-GI conditions than in the control (p < .05). Rating of perceived exertion was lower in the low-GI condition than in the control (p = .01). In a subsample of 5 participants, muscle glycogen availability was greater in the low-and high-GI conditions versus fasted control before the repeated-sprint test (p < .05), with no differences between low and high GI. When exogenous carbohydrates are not provided during exercise both low- and high-GI preexercise meals improve high-intensity, intermittent exercise performance, probably by increasing the availability of muscle glycogen. However, the GI does not influence markers of substrate oxidation during high-intensity, intermittent exercise.
College of Kinesiology, University of Saskatchewan, Saskatoon, SK, Canada.
Jonathan P
JP
Little
Philip D
PD
Chilibeck
Dawn
D
Ciona
Scott
S
Forbes
Huw
H
Rees
Albert
A
Vandenberg
Gordon A
GA
Zello
D000328:Adult; D000704:Analysis of Variance; D054874:Athletic Performance / Q000502:physiology*; D001786:Blood Glucose / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000378:metabolism; D004529:Egg White; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005215:Fasting; D005230:Fatty Acids, Nonesterified / Q000097:blood; D038321:Glycemic Index / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000097:blood; D027806:Lens Plant / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology; D012420:Running / Q000502:physiology; D016037:Single-Blind Method; D011198:Solanum tuberosum / Q000378:metabolism; D013997:Time Factors; D055815:Young Adult
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D006003:Glycogen