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Jane A. Rutherford, Lawrence L. Spriet and Trent Stellingwerff

This study examined whether acute taurine (T) ingestion before prolonged cycling would improve time-trial (TT) performance and alter whole-body fuel utilization compared with a control (CON) trial and a placebo (PL) trial in which participants were told they received taurine but did not. Eleven endurance-trained male cyclists (27.2 ± 1.5 yr, 74.3 ± 2.3 kg, 59.9 ± 2.3 ml · kg−1 · min−1; M ± SEM) completed 3 trials in a randomized, crossover, blinded design in which they consumed a noncaloric sweetened beverage with either 1.66 g of T or nothing added (CON, PL) 1 hr before exercise. Participants then cycled at 66.5% ± 1.9% VO2max for 90 min followed immediately by a TT (doing 5 kJ of work/kg body mass as fast as possible). Data on fluid administration, expired gas, heart rate, and ratings of perceived exertion were collected at 15-min intervals during the 90-min cycling ride, but there were no differences recorded between trials. There was no difference in TT performance between any of the 3 trials (1,500 ± 87 s). Average carbohydrate (T 2.73 ± 0.21, CON 2.88 ± 0.19, PL 2.89 ± 0.20 g/min) and fat (T 0.45 ± 0.05, CON 0.39 ± 0.04, PL 0.39 ± 0.05 g/min) oxidation rates were unaffected by T supplementation. T ingestion resulted in a 16% increase (5 g, ~84 kJ; p < .05) in total fat oxidation over the 90-min exercise period compared with CON and PL. The acute ingestion of 1.66 g of T before exercise did not enhance TT performance but did result in a small but significant increase in fat oxidation during submaximal cycling in endurance-trained cyclists.

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Scott C. Forbes, Vicki Harber and Gordon J. Bell

L-arginine may enhance endurance performance mediated by two primary mechanisms including enhanced secretion of endogenous growth hormone (GH) and as a precursor of nitric oxide (NO); however, research in trained participants has been equivocal. The purpose was to investigate the effect of acute L-arginine ingestion on the hormonal and metabolic response during submaximal exercise in trained cyclists. Fifteen aerobically trained men (age: 28 ± 5 y; body mass: 77.4 ± 9.5 kg; height: 180.9 ± 7.9 cm; VO2max: 59.6 ± 5.9 ml·kg-1·min−1) participated in a randomized, double-blind, crossover study. Subjects consumed L-arginine (ARG; 0.075 g·kg-1 body mass) or a placebo (PLA) before performing an acute bout of submaximal exercise (60 min at 80% of power output achieved at ventilatory threshold). The ARG condition significantly increased plasma L-arginine concentrations (~146%), while no change was detected in the PLA condition. There were no differences between conditions for GH, nonesterified fatty acids (NEFA), lactate, glucose, VO2, VCO2, RER, CHO oxidation, and NOx. There was reduced fat oxidation at the start of exercise (ARG: 0.36 ± 0.25 vs. PLA: 0.42 ± 0.23 g·min−1, p < .05) and an elevated plasma glycerol concentrations at the 45-min time point (ARG: 340.3 vs. PLA: 288.5 μmol·L-1, p < .05) after L-arginine consumption. In conclusion, the acute ingestion of L-arginine did not alter any hormonal, metabolic, or cardio-respiratory responses during submaximal exercise except for a small but significant increase in glycerol at the 45-min time point and a reduction in fat oxidation at the start of exercise.

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Stephen H.S Wong, Oi Won Chan, Ya Jun Chen, Heng Long Hu, Ching Wan Lam and Pak Kwong Chung

Purpose:

This study examined the effect of consuming carbohydrate- (CHO) electrolyte solution on running performance after different-glycemic-index (GI) meals.

Methods:

Nine men completed 3 trials in a randomized counterbalanced order, with trials separated by at least 7 days. Two hours before the run after an overnight fast, each participant consumed a high-GI (GI = 83) or low-GI (GI = 36) CHO meal or low-energy sugar-free Jell-O (GI = 0, control). The 2 isocaloric GI meals provided 1.5 g available CHO/kg body mass. During each trial, 2 ml/kg body mass of a 6.6% CHO-electrolyte solution was provided immediately before exercise and every 2.5 km after the start of running. Each trial consisted of a 21-km performance run on a level treadmill. The participants were required to run at 70% VO2max during the first 5 km of the run. They then completed the remaining 16 km as fast as possible.

Results:

There was no difference in the time to complete the 21-km run (high-GI vs. low-GI vs. control: 91.1 ± 2.0 vs. 91.8 ± 2.2 vs. 92.9 ± 2.0 min, n.s.). There were no differences in total CHO and fat oxidation throughout the trials, despite differences in preexercise blood glucose, serum insulin, and serum free-fatty-acid concentrations.

Conclusion:

When a CHO-electrolyte solution is consumed during a 21-km run, the GI of the preexercise CHO meal makes no difference in running performance.

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Llion A. Roberts, Kris Beattie, Graeme L. Close and James P. Morton

Purpose:

To test the hypothesis that antioxidants can attenuate high-intensity interval training–induced improvements in exercise performance.

Methods:

Two groups of recreationally active males performed a high-intensity interval running protocol, four times per week for 4 wk. Group 1 (n = 8) consumed 1 g of vitamin C daily throughout the training period, whereas Group 2 (n = 7) consumed a visually identical placebo. Pre- and posttraining, subjects were assessed for VO2max, 10 km time trial, running economy at 12 km/h and distance run on the YoYo intermittent recovery tests level 1 and 2 (YoYoIRT1/2). Subjects also performed a 60 min run before and after training at a running velocity of 65% of pretraining VO2max so as to assess training-induced changes in substrate oxidation rates.

Results:

Training improved (P < .0005) VO2max, 10 km time trial, running economy, YoYoIRT1 and YoYoIRT2 in both groups, although there was no difference (P = .31, 0.29, 0.24, 0.76 and 0.59) between groups in the magnitude of training-induced improvements in any of the aforementioned parameters. Similarly, training also decreased (P < .0005) mean carbohydrate and increased mean fat oxidation rates during submaximal exercise in both groups, although no differences (P = .98 and 0.94) existed between training conditions.

Conclusions:

Daily oral consumption of 1 g of vitamin C during a 4 wk high-intensity interval training period does not impair training-induced improvements in the exercise performance of recreationally active males.

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Kimberly M. White, Stephanie J. Bauer, Kristopher K. Hartz and Monika Baldridge

Introduction:

Resistance training is an effective method to decrease body fat (BF) and increase fat-free mass (FFM) and fat oxidation (FO). Dairy foods containing calcium and vitamin D might enhance these benefits. This study investigated the combined effects of habitual yogurt consumption and resistance training on body composition and metabolism.

Methods:

Untrained women (N = 35) participated in an 8-wk resistance-training program. The yogurt group (Y) consumed 3 servings of yogurt containing vitamin D per day, and the control groups maintained their baseline lowdairy-calcium diet. Postexercise, Y consumed 1 of the 3 servings/d fat-free yogurt, the protein group consumed an isocaloric product without calcium or vitamin D, and the carbohydrate group consumed an isocaloric product without protein. Strength, body composition, fasted resting metabolic rate (RMR) and FO, and serum 25-hydroxyvitamin D were measured before and after training.

Results:

Calories (kcal · kg−1 · d−1) and protein (g · kg−1 · d−1) significantly increased from baseline for Y. FFM increased (main effect p = .002) and %BF decreased (main effect .02) for all groups with training, but Group × Time interactions were not observed. RMR and FO did not change with training for any group.

Conclusion:

Habitual consumption of yogurt during resistance training did not augment changes in body composition compared with a low-dairy diet. Y decreased %BF as a result of training, however, even with increased calorie consumption.

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José Moncada-Jiménez, Eric P. Plaisance, Michael L. Mestek, Lance Ratcliff, Felipe Araya-Ramírez, James K. Taylor, Peter W. Grandjean and Luis F. AragónVargas

Purpose:

This study investigated the effects of short-term dietary changes on metabolism and duathlon performance.

Methods:

Eleven men underwent a high-fat (HF; >65% fat from energy) or a high-carbohydrate (CHO; HC) diet (>60% CHO from energy). Energy intake was individualized, and commercially available foods were prepared and packaged for each participant 48 hr before they completed a laboratory-based duathlon (5-km run, 30 km cycling, and 10-km run). Blood samples were obtained before, immediately after, and 1 and 2 hr after the duathlon for determination of glucose, insulin, and glucagon. Oxygen consumption, ratings of perceived exertion (RPE), and respiratory-exchange ratio were assessed, and fat and CHO oxidation were estimated before, during, and after the duathlon.

Results:

Dietary records indicated a significant difference in fat content ingested before the duathlons (p < .05). Time to complete the duathlon did not differ between the HC- and the HF-diet trials. CHO-oxidation rate was higher during the HC-diet trial than during the HF-diet trial (p = .006). Fat-oxidation rates were higher in the HF-diet trial than in the HC-diet trial (p = .001). No differences in RPE were found between dietary trials. Blood glucose concentration was higher immediately after the duathlon in the HC-diet trial than in the HF-diet trial and remained higher 1 and 2 hr after the duathlon (p < .05).

Conclusion:

Duathlon performance was not altered by short-term changes in dietary fat or CHO composition despite higher blood glucose concentrations under the HC condition.

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Jie Kang, Robert J. Robertson, Bart G. Denys, Sergio G. DaSilva, Paul Visich, Richard R. Suminski, Alan C. Utter, Fredric L. Goss and Kenneth F. Metz

This investigation determined whether carbohydrate ingestion during prolonged moderate-intensity exercise enhanced endurance performance when the exercise was preceded by carbohydrate supercompensation. Seven male trained cyclists performed two trials at an initial power output corresponding to 71 ± 1 % of their peak oxygen consumption. During the trials, subjects ingested either a 6% glucose/sucrose (C) solution or an equal volume of artificially flavored and sweetened placebo (P) every 20 min throughout exercise. Both C and P were preceded by a 6-day carbohydrate supercompensation procedure in which subjects undertook a depletion-taper exercise sequence in conjunction with a moderate- and high-carbohydrate diet regimen. Statistical analysis of time to exhaustion, plasma glucose concentration, carbohydrate oxidation rate, fat oxidation rate, and plasma glycerol concentration indicated that in spite of a carbohydrate supercompensation procedure administered prior to exercise, carbohydrate ingestion during exercise can exert an additional ergogenic effect by preventing a decline in blood glucose levels and maintaining carbohydrate oxidation during the later stages of moderate-intensity exercise.

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Trent Stellingwerff

Anecdotal claims have suggested that an increasing number of ultramarathoners purposely undertake chronic low-carbohydrate (CHO) ketogenic diets while training, and race with very low CHO intakes, as a way to maximize fat oxidation and improve performance. However, very little empirical evidence exists on specific fueling strategies that elite ultramarathoners undertake to maximize race performance. The study’s purpose was to characterize race nutrition habits of elite ultramarathon runners. Three veteran male ultrarunners (M ± SD; age 35 ± 2 years; mass 59.5 ± 1.7 kg; 16.7 ± 2.5 hr 100-mi. best times) agreed to complete a competition-specific nutrition intake questionnaire for 100-mi. races. Verbal and visual instructions were used to instruct the athletes on portion sizes and confirm dietary intake. Throughout 2014, the athletes competed in 16 ultramarathons with a total of 8 wins, including the prestigious Western States Endurance Run 100-miler (14.9 hr). The average prerace breakfast contained 70 ± 16 g CHO, 29 ± 20 g protein, and 21 ± 8 g fat. Athletes consumed an average of 1,162 ± 250 g of CHO (71 ± 20g/hr), with minor fat and protein intakes, resulting in caloric intakes totaling 5,530 ± 1,673 kcals (333 ± 105 kcals/hr) with 93% of calories coming from commercial products. Athletes also reported consuming 912 ± 322 mg of caffeine and 6.9 ± 2.4 g of sodium. Despite having limited professional nutritional input into their fueling approaches, all athletes practiced fueling strategies that maximize CHO intake and are congruent with contemporary evidence-based recommendations.

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Ching-Lin Wu and Clyde Williams

This study investigated the effects of ingesting a low (LGI) or high (HGI) glyce-mic index carbohydrate (CHO) meal 3 h prior to exercise on endurance running capacity. Eight male recreational runners undertook two trials (LGI or HGI) which were randomized and separated by 7 d. After an overnight fast (12 h) the subjects ingested either a LGI or HGI meal 3 h prior to running at 70% VO2max until exhaustion. The meals contained 2 g/kg body mass CHO and were isocaloric and iso-macronutrient with calculated GI values 77 and 37 for the HGI and LGI respectively. The run times for the LGI and HGI trials were 108.8 ± 4.1 min and 101.4 ± 5.2 min respectively (P = 0.038). Fat oxidation rates were higher during exercise after the LGI meal than after the HGI meal (P < 0.05). In summary, ingestion of a LGI meal 3 h before exercise resulted in a greater endurance capacity than after the ingestion of a HGI meal.

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Laura J.S. Moore, Adrian W. Midgley, Gemma Thomas, Shane Thurlow and Lars R. McNaughton

Purpose:

The aim of this work was to determine whether the consumption of pre-exercise high– or low–glycemic index (GI) meals has a beneficial effect on time trial performance.

Methods:

Eight male cyclists were provided with either a high-GI or low-GI meal, providing 1 g·kg−1 body mass of carbohydrate, 45 min before performing a 40-km time trial on a Velotron cyclePro.

Results:

Time trial performance was significantly improved in the low-GI trial (92.5 ± 5.2 min) compared with the high-GI trial (95.6 ± 6.0 min) (P = .009). Blood glucose concentrations at the point of exhaustion were significantly higher in the low-GI trial (5.2± 0.6 mmol·L−1) compared with the high-GI trial (4.7 ± 0.7 mmol·L−1) (P = .001). There was no significant difference in estimated carbohydrate oxidation data between the low-GI (2.51 ± 1.74 g·min−1) and high-GI (2.18 ± 1.53 g·min−1) meals (P = .195). No significant difference in estimated fat oxidation was observed between the low-GI (0.15 ± 0.15 g·min−1) and high-GI (0.29 ± 0.18 g·min−1) diets (P = .83).

Conclusions:

The improvement in time trial performance for the low-GI trial may be associated with an increased availability of glucose to the working muscles, contributing additional carbohydrate for oxidation and possibly sparing limited muscle and liver glycogen stores.