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  • Author: Gordon A. Zello x
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Jonathan P. Little, Philip D. Chilibeck, Dawn Ciona, Albert Vandenberg and Gordon A. Zello

The glycemic index (GI) of a pre exercise 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 fve 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.

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Jonathan P. Little, Philip D. Chilibeck, Dawn Ciona, Scott Forbes, Huw Rees, Albert Vandenberg and Gordon A. Zello

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.

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Stephen M. Cornish, Darren G. Candow, Nathan T. Jantz, Philip D. Chilibeck, Jonathan P. Little, Scott Forbes, Saman Abeysekara and Gordon A. Zello

Purpose:

The authors examined the combined effects of conjugated linoleic acid (CLA), creatine (C), and whey protein (P) supplementation during strength training.

Methods:

Sixty-nine participants (52 men, 17 women; M ± SD age 22.5 ± 2.5 yr) were randomly assigned (double-blind) to 1 of 3 groups: CCP (6 g/d CLA + 9 g/d C + 36 g/d P; n = 22), CP (C + P + placebo oil; n = 25), or P (P + placebo oil; n = 22) during 5 wk of strength training (4–5 sets, 6–12 repetitions, 6 d/wk). Measurements were taken for body composition (air-displacement plethysmography), muscle thickness (ultrasound) of the flexors and extensors of the elbow and knee, 1-repetitionmaximum (1-RM) strength (leg press and bench press), urinary markers of bone resorption (N-telopeptides, NTx), myofibrillar protein catabolism (3-methylhistidine; 3-MH), oxidative stress (8-isoprostanes), and kidney function (microalbumin) before and after training.

Results:

Contrast analyses indicated that the CCP group had a greater increase in bench-press (16.2% ± 11.3% vs. 9.7% ± 17.0%; p < .05) and legpress (13.1% ± 9.9% vs. 7.7% ± 14.2%; p < .05) strength and lean-tissue mass (2.4% ± 2.8% vs. 1.3% ± 4.1%; p < .05) than the other groups combined. All groups increased muscle thickness over time (p < .05). The relative change in 3-MH (CCP –4.7% ± 70.2%, CP –0.4% ± 81.4%, P 20.3% ± 75.2%) was less in the groups receiving creatine (p < .05), with the difference for NTx also close to significance (p = .055; CCP–3.4% ± 66.6%, CP–3.9% ± 64.9%, P 26.0% ± 63.8%). There were no changes in oxidative stress or kidney function.

Conclusion:

Combining C, CLA, and P was beneficial for increasing strength and lean-tissue mass during heavy resistance training.