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.

The glycemic index (GI) of a preexercise meal may affect substrate utilization and performance during continuous exercise. Purpose: To examine the effects of low-and high-GI foods on metabolism and performance during high-intensity, intermittent exercise. Methods: Seven male athletes participated in three experimental trials (low-GI, high-GI, and fasted control) separated by ~7 days. Foods were consumed 3 h before (~1.3 g·kg −1 carbohydrate) and halfway through (~0.2 g·kg −1 carbohydrate) 90 min of intermittent treadmill running designed to simulate the activity pattern of soccer. Expired gas was collected during exercise to estimate substrate oxidation. Performance was assessed by the distance covered on five 1-min sprints during the last 15 min of exercise. Results: Respiratory exchange ratio was higher and fat oxidation lower during exercise in the high-GI condition compared with fasting (P < .05). The mean difference in total distance covered on the repeated sprint test between low GI and fasting (247 m; 90% confidence limits ±352 m) represented an 81% (likely, probable) chance that the low-GI condition improved performance over fasting. The mean difference between high GI and fasted control (223 m; ±385 m) represented a 76% (likely, probable) chance of improved performance. There were no differences between low and high GI. Conclusions: When compared with fasting, both low-and high-GI foods consumed 3 h before and halfway through prolonged, high-intensity intermittent exercise improved repeated sprint performance. High-GI foods impaired fat oxidation during exercise but the GI did not appear to influence high-intensity, intermittent exercise performance.Athletes are advised that consuming carbohydrate meals before exercise improves endurance; 1-5 however, the characteristics of the ideal preexercise meal remain largely unknown. The glycemic index (GI) of carbohydrates ingested Little and Chilibeck are with the College

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Our objective was to examine the acceptance, and effects on metabolism and performance of lentils as a pre‐exercise meal in a simulated soccer match. Thirteen male athletes participated in 4 trials in a repeated crossover design. Along with a fasted control (C) condition, isocaloric low GI‐high protein [lentils (L)], high GI‐high protein [potato & egg whites (PE)], or high GI‐low protein [potato (P)] meals were consumed 2‐hr before a soccer match. Blood and expired gas samples were collected to assess macronutrient metabolism. Distance covered on 5×1‐min sprints (2.5‐min rest) performed at the end of the match assessed performance. A 5‐point Symptoms Rating Scale (SRS) was used to assess nausea, bloating, hunger, fullness and flatulence. Serum insulin at exercise initiation was higher in P than all other conditions (p<0.001). During exercise, the oxidation rates for carbohydrate was higher and for fat was lower in P compared to C (p<0.05). Initial distance covered was greater (sprints 1 & 2) for L and PE (sprint 2) than fasting. Ratings of perceived exertion (RPE) throughout exercise were lower in L compared to C and P (p<0.05). No differences in symptoms (SRS) were apparent among the fed conditions (p>0.05). Also, the % of meals consumed was similar (80, 81 & 78% for L, PE & P, respectively). Our results show improvements in initial repeated sprint performance after L and PE meals compared to C. This finding along with the L meal's low RPE and its acceptability indicates a possible beneficial effect of consuming a low GI‐high protein pre‐exercise L meal. (Supported by research grants from the Saskatchewan Pulse Growers and NSERC Canada)