Effects of carbohydrate intake on time to exhaustion and anaerobic contribution during supramaximal exercise

1 Universidade Federal de Alagoas, Departamento de Educação Física, Programa de Pós-Graduação em Nutrição, Grupo de Pesquisa em Ciências Aplicadas ao Esporte. Av. Lourival Melo Mota, s/n., Tabuleiro dos Martins, Maceió, AL, Brasil. Correspondência para/Correspondence to: GG ARAUJO. E-mail: <gusta_ef@yahoo.com.br>. 2 Universidade Federal de Pernambuco, Centro Acadêmico de Vitória, Grupo de Pesquisa em Ciências do Esporte. Vitória de Santo Antão, PE, Brasil. ORIGINAL | ORIGINAL


I N T R O D U C T I O N
Some studies have found that carbohydrate intake before prolonged exercise (>60 min) can improve performance 1,2 .Recently, it has been reported that the intake of a carbohydrate drink 30 min before high-intensity exercise at 90% of peak power output improved performance by 17% compared with placebo 3 .Although these authors speculated that pre-exercise blood glucose enhance can increase glucose absorption and oxidation during skeletal muscle contraction due to higher activity of the pyruvate dehydrogenase complex, alactic and lactic anaerobic metabolisms were not measured during the tests.Bergström & Hultman 4 found that muscle glycogen is not completely depleted during high-intensity exercises, so it is not a limiting factor for exercise performance.Moreover, higher availability of muscle glycogen after a high-carbohydrate meal has no effect on performance during highintensity exercise 5,6 .A plausible explanation for better performance in high-intensity exercises after carbohydrate intake is higher neuromuscular activation, which may lead to higher recruitment of type IIx fibers 7 and concomitantly increase anaerobic glycolysis 8 .Higher neuromuscular activation may be explained by activation of the cerebral cortex due to oral carbohydrate sensing, intermediated by the carbohydrate receptors in the mouth 9 .Oral carbohydrate sensing may increase neuromuscular activation 10 and activation of brain areas responsible for motivation, including the frontal operculum/insula, and orbitofrontal cortex and striatum 11,12 .However, it is not entirely known whether these ergogenic effects can be extended to short-term supramaximal exercises (~3 min) and improve anaerobic contribution [13][14][15][16] .http://dx.doi.org/10.1590/1678-98652016000500007Therefore, the objective of this study was to analyze the effect of carbohydrate intake on time to exhaustion and anaerobic contribution during supramaximal exercise.Carbohydrate intake may improve performance, that is, increase time to exhaustion, by promoting higher neuromuscular recruitment 10 secondary to oral carbohydrate sensing 9 , thereby generating higher anaerobic contribution.

M E T H O D S
The study included ten volunteers with a mean age of 23.9±2.5 years, mean body mass of 75.1±12.3kg, mean height of 170.0±1.0 cm, mean body fat of 11.3±5.2%,and mean VO 2máx of 42.1±5.2mL•kg -1 •min -1 .All volunteers were healthy and physically active men who performed at least 150 min of physical activity per week.Before enrollment, the participants were fully informed in writing and verbally about the study purpose and risks.Each participant signed an informed consent form before starting the tests.The experimental protocol complied with the Declaration of Helsinki 2008 and was approved by the local Universidade Federal de Alagoas (Federal University of Alagoas) Research Ethics Committee under protocol nº 1420/12.This is a blind, counterbalanced, crossover study.The participants performed three experimental sessions with a minimum interval of 72h.During the first visit, anthropometric parameters were measured and an incremental test was conducted to determine maximal oxygen uptake (VO 2max ) and maximal power output.During the second and third visits, a supramaximal test at 110% of maximal power output was conducted to voluntary exhaustion after carbohydrate or placebo interventions.All tests were conducted at the same time of day, two hours after the last meal 17 .The participants were instructed to replicate their food intake 24h before each experimental test, and before each test the researchers verified whether the recommendations had been followed.The participants were instructed to avoid exhaustive exercise, and alcohol and caffeine intakes in the 48h that preceded each experimental test.
Thirty minutes before the test, the participants consumed 200 mL of water with 2 g.kg -1 of body weight of maltodextrin (carbohydrate) or juice without carbohydrate (placebo) but with the same flavor, aroma, and texture.The participants then rested until assessment.
The body mass of the participants was measured by a scale with an accuracy of 0.1 kg.Height was measured by a stadiometer with an accuracy of 0.1 cm.Skinfold thicknesses (thorax, abdominal, and thigh) were measured by a Lange adipometer in a scale of 0 to 60 mm, resolution of one millimeter, and a spring with constant pressure of 10 g/mm 2 .Body density was predicted by the generalized equation proposed by Jackson & Pollock 18 , and body fat was estimated by the equation proposed by Siri 19 .
The incremental test was performed on an electromagnetically braked cycle ergometer (Ergo Fit 167, Ergo-Fit GmbH & Co., Pirmasens, Germany).Saddle height was adjusted for each participant allowing almost full extension of the leg during each cycle.These conditions were repeated for all experimental sessions.After a warmup of 3 min at 30 W, the power was increased to 30 W.min -1 , and cadence was maintained between 60 and 70 rpm until voluntary exhaustion, which was defined as the inability to maintain a minimal cadence of 60 rpm.The participants were cheered to cycle as long as possible.
Oxygen uptake (VO 2 ) was measured at each breath by a gas analyzer (Quark, Cosmed, Rome, Italy) and assessed at roughly every 30s.The device was calibrated as instructed by the manufacturer, using room air, a gas containing 20.9% of O 2 and 5% of CO 2 , and a 3 L syringe.VO 2máx was determined when two or more of the following criteria were met: a VO 2 increase smaller than 2.1 mL•kg -1 •min -1 on two consecutive stages, a respiratory exchange ratio higher than 1.  20 .The maximal power output was based on the VO 2máx stage.
A supramaximal test was conducted at 110% of the maximal power output.This intensity was chosen because of the study conducted by Weber & Schneider 21 to estimate maximal anaerobic contribution using the maximal accumulated oxygen deficit proposed by Bertuzzi et al. 22 .
The participants remained inactive on the cycle ergometer for five min to determine baseline VO 2 .The participants then warmed up for four min at 30 W. Next, the power was adjusted to 110% of the maximal power output.The participants were instructed to maintain a cadence of 60 to 70 rpm.The test ended when cadence fell below 60 rpm for more than 5s or for a fourth time.The participants were again cheered during the whole test.The peak oxygen uptake (VO 2peak ) was defined as the mean of the last 30s of the test.Blood samples were collected from the ear lobe before and immediately, 3 min, and 5 min after the exercise.Peak blood lactate ([La-] peak ) was defined as the highest value obtained after the test.
Anaerobic contribution was calculated as recommended by Bertuzzi et al. 22 .In summary, the breath-by-breath of the VO 2 off-transient response was adjusted by a two-exponential model, and the area under the curve of the first exponential was calculated to estimate the alactic contribution (Origin 6.0, Microcal, Massachusetts, USA).The difference between [La -] peak and [La -] rest during the supramaximal test was expressed as a difference ([La -] net ) and converted to oxygen uptake using the equation proposed by Di Prampero & Ferretti 23 , that is, 1 mmoLL -1 [La -] net is equal to 3 mL O 2 •kg -1 of body weight to estimate lactic contribution.Total anaerobic contribution was obtained by adding the alactic and lactic contributions.The values were then divided by one thousand to convert milliliters to liters.
The Shapiro-Wilk test analyzed data distribution.The data were expressed as mean and standard deviation.The paired Student's t-test compared the differences between the carbohydrate and placebo interventions.The significance level was set at 5% (p<0.05).All statistical calculations were performed by the software Statistical Package for the Social Sciences (SPSS Inc., Chicago, Illinois, United States) version 17.0 for Windows.
The effect size was calculated for all carbohydrate and placebo variables.The thresholds for the small, moderate, and large effects were 0.20, 0.50, and 0.80, respectively.The effect size was determined by the formula: (mean1 -mean2) / grouped standard deviation 24 .
Additionally, some studies found that baseline muscle glycogen content does not affect muscle glycogen breakdown during high-intensity exercises.This may explain why carbohydrate intake and a high-carbohydrate diet do not affect time to exhaustion and anaerobic contribution during supramaximal exercise 6,27,28 .In this context, the study data reinforce the abovementioned results, showing that, like higher muscle glycogen content, an exogenous carbohydrate source has no positive effect on performance and anaerobic contribution during supramaximal exercise 5 .Although performance and anaerobic contribution did not change significantly, peak blood lactate had a moderate effect size (0.57), possibly because of higher pyruvate dehydrogenase complex activity, as reported by Galloway et al. 3 .
With respect to the ergogenic effect of oral carbohydrate sensing on performance, most studies have reported improvements during exercises at intensities below VO 2max (~75%ofVO 2max ).Studies using anaerobic tasks 29 and resistance training 30 did not find a positive effect of oral carbohydrate sensing on performance, possibly because exercises at submaximal intensities recruit only some motor units while supramaximal exercises can recruit nearly all motor units 31 .This fact may minimize any oral carbohydrate sensing effect during supramaximal exercises.Hence, as practical application, the present study reinforces the hypothesis that carbohydrate intake before short-term highintensity exercises does not seem to be an effective strategy to improve performance.
One of the possible study limitations is the time between tests.The initial proposal was of a minimum interval of 72 hours.However, some

D I S C U S S I O N
Apparently this is the first study that investigated the effects of pre-exercise carbohydrate intake on time to exhaustion and anaerobic contribution during supramaximal exercise.The study results encourage interesting considerations about the ergogenic effects of carbohydrate intake, indicating that such intake does not seem capable of increasing time to exhaustion and anaerobic contribution during supramaximal exercise in physically active men.
Carbohydrate supplementation can delay fatigue onset and concomitantly, increase time to exhaustion during exercises with intensities ranging from 70% to 90% of peak power [1][2][3]25,26 . Howevr, the effects of pre-exercise carbohydrate intake on supramaximal exercise are not well known.The study results suggest that time to exhaustion does not improve significantly during an exercise at 110% of maximal power output.Some pieces of evidence suggest that pre-exercise carbohydrate intake increases performance during high-intensity exercise.Galloway et al. 3 found an increase in time to exhaustion at 90% of peak power output when their subjects ingested 500 mL of a drink containing carbohydrates and electrolytes (6.4% carbohydrate, 32 g) 30 min before exercise compared with a placebo with same flavor and color (0.1% carbohydrate).The length of the postprandial period may explain this discrepancy.Galloway et al. 3

Figure 1 .
Figure 1.Total anaerobic contribuition in the placebo and carbohydrate intervention.
used an overnight fast (>10h), which may lead to considerable Rev. Nutr., Campinas, 29(5):691-697, set./out., 2016 Revista de Nutrição http://dx.doi.org/10.1590/1678-98652016000500007subjects performed the second supramaximal test after a 96h recovery period.Another possible limitation may be the physical fitness of our sample.More physically fit subjects could be more sensitive to the study effects.C O N C L U S I O NCarbohydrate intake did not increase time to exhaustion or anaerobic contribution during supramaximal exercise in physically active men.A C K N O W L E D G M E N T SWe thank the Laboratory of Physical Fitness, Performance, and Health of the Federal University of Alagoas and the sponsor Research Support Foundation of the State of Alagoas.C O N T R I B U T O R SVB SILVA and SK LEARSI participated in the elaboration of the experimental design, data collection, tabulation, discussion and writing of the manuscript.AA MELO participated in data collection, data discussion and writing of the manuscript.AE LIMA-SILVA and GG ARAUJO participated in the preparation of the research project, in the elaboration of the experimental design, data discussion as well as writing and correction of the manuscript.

Table 1 .
Peak lactate, and percentage lactic and alactic contributions.