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Training for Performance: Insights From Molecular Biology

Vernon G. Coffey and John A. Hawley

In this commentary the authors discuss the molecular basis of the training adaptation and review the role of several key signaling proteins important in the adaptation to endurance and resistance training.

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Reduced Neuromuscular Activity with Carbohydrate Ingestion during Constant Load Cycling

Vasilis Nikolopoulos, Melissa J. Arkinstall, and John A. Hawley

The purpose of this study was to determine the effect of carbohydrate ingestion before and during intense constant load cycling to volitional fatigue on surface electromyographic (sEMG) activity from the vastus lateralis (VL) and vastus medialis (VM) muscles. After 24-h diet and training control, 8 well-trained subjects [maximal O2 uptake (VO2max) 66 ± 2 ml · kg–1· min–1; mean ± SD] ingested 8 ml · kg–1 of either a 6.4% carbohydrate-electrolyte (CHO) or a placebo (PLA) solution immediately before, followed by 2 ml · kg–1 of the same solution every 15 min while cycling to exhaustion at 84 ± 1% of VO2max. Exercise time to fatigue was 13% longer with CHO ingestion compared to PLA (58:54 ± 8:48 vs. 51:18 ± 5:54 min:s, NS). VO2 (4.22 ± 0.11 vs. 4.20 ± 0.14 L · min–1), heart rate (172 ± 4 vs. 176 ± 4 beats · min–1), ratings of perceived effort (18 ± 0.1 vs. 19 ± 0.1), and rates of carbohydrate oxidation (314 ± 28 vs. 324 ± 26 μmol · kg–1 · min–1) were similar for both PLA and CHO at exhaustion. There was no main treatment effect of CHO ingestion on blood glucose or lactate concentrations, nor plasma prolactin levels either during exercise or at fatigue. However, CHO ingestion attenuated the rise in EMG root mean square (RMS) activity during the latter stages (>45 min) of exercise and at the point of exhaustion for both VM (0.325 ± 0.010 vs. 0.403 ± 0.020 mV; p = .006) and VL (0.298 ± 0.011 vs. 0.370 ± 0.007 mV; p = .0004). We conclude that in well-trained subjects, the ingestion of carbohydrate attenuated the increase in surface electromyographic activity during intense, constant load cycling leading to exhaustion in ~1 h. The precise mechanism(s) underlying this effect cannot be attributed to alterations in CHO availability but, instead, may be linked to changes in afferent sensory input.

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Carbohydrate, Fluids and Electrolyte Requirements of the Soccer Player: A Stewiew

John A. Hawley, Steven C. Dennis, and Timothy D. Noakes

Soccer requires field players to exercise repetitively at high intensities for the duration of a game, which can result in marked muscle glycogen depletion and hypoglycemia. A soccer match places heavy demands on endogenous muscle and liver glycogen stores and fluid reserves, which must be rapidly replenished when players complete several matches within a brief period of time. Low concentrations of muscle glycogen have been reported in soccer players before a game, and daily carbohydrate (CHO) intakes are often insufficient to replenish muscle glycogen stores, CHO supplementation during soccer matches has been found to result in muscle glycogen sparing (39%), greater second-half running distances, and more goals being scored with less conceded, when compared to consumption of water. Thus, CHO supplementation has been recommended prior to, during, and after matches. In contrast, there is currently insufficient evidence to recommend without reservation the addition of electrolytes to a beverage for ingestion by players during a game resulting in sweat losses of < 4% of body weight.

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Short-Term High-Fat Diet Alters Substrate Utilization during Exercise but Not Glucose Tolerance in Highly Trained Athletes

Heidi M. Staudacher, Andrew L. Carey, Nicola K. Cummings, John A. Hawley, and Louise M. Burke

We determined the effect of a high-fat diet and carbohydrate (CHO) restoration on substrate oxidation and glucose tolerance in 7 competitive ultra-endurance athletes (peak oxygen uptake [V̇O2peak] 68 ± 1 ml · kg−1 · min−1; mean±SEM). For 6 days, subjects consumed a random order of a high-fat (69% fat; FAT-adapt) or a high-CHO (70% CHO; HCHO) diet, each followed by 1 day of a high-CHO diet. Treatments were separated by an 18-day wash out. Substrate oxidation was determined during submaximal cycling (20 min at 65% V̇O2peak) prior to and following the 6 day dietary interventions. Fat oxidation at baseline was not different between treatments (17.4 ± 2.1 vs. 16.1 ± 1.3 g · 20 min−1 for FAT-adapt and HCHO, respectively) but increased 34% after 6 days of FAT-adapt (to 23.3 ± 0.9 g · 20 min−1, p < .05) and decreased 30% after HCHO (to 11.3±1.4 g · 20 min−1, p < .05). Glucose tolerance, determined by the area under the plasma [glucose] versus time curve during an oral glucose tolerance (OGTT) test, was similar at baseline (545±21 vs. 520±28 mmol · L−1 · 90 min−1), after 5-d of dietary intervention (563 ± 26 vs. 520 ± 18 mmol · L−1 · 90 min−1) and after 1 d of high-CHO (491 ± 28 vs. 489 ± 22 mmol · L−1 · 90min−1 for FAT- adapt and HCHO, respectively). An index of whole-body insulin sensitivity (SI 10000/÷fasting [glucose] × fasting [insulin] × mean [glucose] during OGTT × mean [insulin] during OGTT) was similar at baseline (15 ± 2 vs. 17 ± 5 arbitrary units), after 5-d of dietary intervention (15 ± 2 vs. 15 ± 2) and after 24 h of CHO loading (17 ± 3 vs. 18 ± 2 for FAT- adapt and HCHO, respectively). We conclude that despite marked changes in the pattern of substrate oxidation during submaximal exercise, short-term adaptation to a high-fat diet does not alter whole-body glucose tolerance or an index of insulin sensitivity in highly-trained individuals.

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Single and Combined Effects of Beetroot Crystals and Sodium Bicarbonate on 4-km Cycling Time Trial Performance

Marcus J. Callahan, Evelyn B. Parr, John A. Hawley, and Louise M. Burke

When ingested alone, beetroot juice and sodium bicarbonate are ergogenic for high-intensity exercise performance. This study sought to determine the independent and combined effects of these supplements. Eight endurance trained (VO2max 65 mL·kg·min-1) male cyclists completed four × 4-km time trials (TT) in a doubleblind Latin square design supplementing with beetroot crystals (BC) for 3 days (15 g·day-1 + 15 g 1 h before TT, containing 300 mg nitrate per 15 g), bicarbonate (Bi 0.3 g·kg-1 body mass [BM] in 5 doses every 15 min from 2.5 h before TT); BC+Bi or placebo (PLA). Subjects completed TTs on a Velotron cycle ergometer under standardized laboratory conditions. Plasma nitrite concentrations were significantly elevated only in the BC+Bi trial before the TT (1520 ± 786 nmol·L-1) compared with baseline (665 ± 535 nmol·L-1, p = .02) and the Bi and PLA conditions (Bi: 593 ± 203 nmol·L-1, p < .01; PLA: 543 ± 369 nmol·L-1, p < .01). Plasma nitrite concentrations were not elevated in the BC trial before the TT (1102 ± 218 nmol·L-1) compared with baseline (975 ± 607 nmol·L-1, p > .05). Blood bicarbonate concentrations were increased in the BC+Bi and Bi trials before the TT (BC+Bi: 30.9 ± 2.8 mmol·L-1; Bi: 31.7 ± 1.1 mmol·L-1). There were no differences in mean power output (386–394 W) or the time taken to complete the TT (335.8–338.1 s) between any conditions. Under the conditions of this study, supplementation was not ergogenic for 4-km TT performance.

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Letters to the Editor

Daniel A. Boullosa, Fábio Y. Nakamura, Jonatan R. Ruiz, Stephen Seiler, Jonathan Esteve-Lanao, Alejandro Lucia, John A. Hawley, and David T. Martin

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Improved 2000-Meter Rowing Performance in Competitive Oarswomen after Caffeine Ingestion

Megan E. Anderson, Clinton R. Bruce, Steve F. Fraser, Nigel K. Stepto, Rudi Klein, William G. Hopkins, and John A. Hawley

Eight competitive oarswomen (age, 22 ± 3 years; mass, 64.4 ± 3.8 kg) performed three simulated 2,000-m time trials on a rowing ergometer. The trials, which were preceded by a 24-hour dietary and training control and 72 hours of caffeine abstinence, were condueted 1 hour after ingesting caffeine (6 or 9 mg kg ’ body mass) or placebo. Plasma free fatty acid concentrations before exercise were higher with caffeine than placebo (0.67 ± 0.34 vs. 0.72 ± 0.36 vs. 0.30±0.10 mM for 6 and 9 mg · kg−1; caffeine and placebo, respectively; p <.05). Performance lime improved 0.7% (95% confidence interval [Cf] 0 to 1.5%) with 6 mg kg−1 caffeine and 1.3$ (95% CI 0.5 to 2.0%) with 9 mg · kg−1 caffeine. The first 500 m of the 2,000 m was faster with the higher caffeine dose compared with placebo or the lower dose (1.53 ± 0.52 vs. 1.55 ± 0.62 and 1.56 ± 0.43 min; p = .02). We concluded that caffeine produces a worthwhile enhancement of performance in a controlled laboratory setting, primarily by improving the first 500 m of a 2,000-m row.

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High-Fat Diet versus Habitual Diet Prior to Carbohydrate Loading: Effects on Exercise Metabolism and Cycling Performance

Estelle V. Lambert, Julia H. Goedecke, Charl van Zyl, Kim Murphy, John A. Hawley, Steven C. Dennis, and Timothy D. Noakes

We examined the effects of a high-fat diet (HFD-CHO) versus a habitual diet, prior to carbohydrate (CHO)-loading on fuel metabolism and cycling time-trial (TT) performance. Five endurance-trained cyclists participated in two 14-day randomized cross-over trials during which subjects consumed either a HFD (>65% MJ from fat) or their habitual diet (CTL) (30 ± 5% MJ from fat) for 10 day, before ingesting a high-CHO diet (CHO-loading, CHO > 70% MJ) for 3 days. Trials consisted of a 150-min cycle at 70% of peak oxygen uptake (V̇O2peak), followed immediately by a 20-km TT. One hour before each trial, cyclists ingested 400 ml of a 3.44% medium-chain triacylglycerol (MCT) solution, and during the trial, ingested 600 ml/hour of a 10% 14C-glucose + 3.44% MCT solution. The dietary treatments did not alter the subjects’ weight, body fat, or lipid profile. There were also no changes in circulating glucose, lactate, free fatty acid (FFA), and β-hydroxybutyrate concentrations during exercise. However, mean serum glycerol concentrations were significantly higher (p < .01) in the HFD-CHO trial. The HFD-CHO diet increased total fat oxidation and reduced total CHO oxidation but did not alter plasma glucose oxidation during exercise. By contrast, the estimated rates of muscle glycogen and lactate oxidation were lower after the HFD-CHO diet. The HFD-CHO treatment was also associated with improved TT times (29.5 ± 2.9 min vs. 30.9 ± 3.4 min for HFD-CHO and CTL-CHO, p < .05). High-fat feeding for 10 days prior to CHO-loading was associated with an increased reliance on fat, a decreased reliance on muscle glycogen, and improved time trial performance after prolonged exercise.

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The Effect of Carbohydrate Ingestion on the Motor Skill Proficiency of Soccer Players

Clayton Zeederberg, Lloyd Leach, Estelle V. Lambert, Timothy D. Noakes, Steven C. Dennis, and John A. Hawley

This study examined the effects of ingesting a glucose-polymer (GP) solution on the motor skill proficiencies of association football (soccer) players from two teams playing during two matches in a cool environment. Fifteen minutes before each match and at halftime, players from both teams ingested 5 ml/kg of either placebo or a 6.9% GP solution. GP ingestion did not improve tackling, heading, dribbling, or shooting ability. On the contrary, the mean of successful tackles was lower with GP ingestion than with placebo. The success rate for heading, dribbling, and shooting also tended to be lower in the GP than in the placebo condition. In contrast, success in passing and ball control was similar in the two conditions. Improvements in passing and ball control may have been related to a decrease in the intensity of play in the second half of the game. These data indicate that there are no measurable benefits of GP ingestion for the motor skill proficiencies of soccer players during games played in a cool environment.

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The Effects of Carbohydrate Loading on Muscle Glycogen Content and Cycling Performance

Laurie H.G. Rauch, Ian Rodger, Gary R. Wilson, Judy D. Belonje, Steven C. Dennis, Timothy D. Noakes, and John A. Hawley

This study compared the effects of supplementing the normal diets of 8 endurance-trained cyclists with additional carbohydrate (CHO), in the form of potato starch, for 3 days on muscle glycogen utilization and performance during a 3-hr cycle ride. On two occasions prior to the trial, the subjects ingested in random order either their normal CHO intake of 6.15 ± 0.23 g/kg body mass/day or a high-CHO diet of 10.52 ± 0.57 g/kg body mass/day. The trial consisted of 2 hr of cycling at ~75% of VO 2 peak with five 60-s sprints at 100% VO 2 peak at 20-min intervals, followed by a 60-min performance ride. Increasing CHO intake by 72 ± 9% for 3 days prior to the trial elevated preexercise muscle glycogen contents, improved power output, and extended the distance covered in 1 hr. Muscle glycogen contents were similar at the end of the 3-hr trial, indicating a greater utilization of glycogen when subjects were CHO loaded, which may have been responsible for their improved cycling performance.