Carbohydrate Mouth Rinse and Hydration Strategies on Cycling Performance in 30 Km Time Trial: A Randomized, Crossover, Controlled Trial.

Author:Ferreira, Amanda M.J.
Position::Research article - Report
 
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Introduction

Cycling time trials are characterized by shorter duration, high intensity and high pedaling cadence (Luria et al., 1999; Luda et al., 2001). In cycling competitions, the intensity is higher than 70% of maximum oxygen consumption ([VO.sub.2max]) and it can reach 90% among elite cyclists (Fernandez-Garda et al., 2000; Luda et al., 1999; Neumayr et al., 2002). Energy expenditure and cardiopulmonary high demand during cycling competitions challenges water loss control, which has an important role in thermoregulation control (Jeukendrup, 2011; Maughan and Meyer, 2013), and also in depletion of muscle glycogen stores during exercise (Garber et al., 2011; Lepers et al., 2002). Hence, excessive bodily

fluid loss (> 2% of body mass), in the form of dehydration, impairs an athlete s physical performance, especially in a hot and humid environment (Maughan and Meyer, 2013; Maughan, 2012; Sawka et al., 2007).

The sports federations advise athletes to drink enough fluid to replace sweat losses during exercise or consume the maximal amount that can be tolerated (Sawka et al., 2007; Thomas et al. , 2016). In addition, electrolyte replacement should be considered when exercise leads to high sweat rates, exceeding 900ml/h (Hernandez and Nahas, 2009; Sawka et al., 2007). On the other hand, researchers argue that free-choice fluid intake ("ad libitum") is sufficient to maintain homeostasis (Berkulo et al., 2015; Noakes, 2007; Wall et al., 2015). They believe that the central nervous system is able to indicate the correct fluid volume to be ingested according to afferent information, ensuring control of plasma levels and body temperature (Daries et al., 2000; Goulet, 2011; Machado-Moreira et al., 2006; Noakes et al., 2005; Noakes, 2007). These reports have increased adoption of the "ad libitum" strategy, especially in time trials in which high intensity raises the chance of athletes complaining about gastrointestinal discomfort or the risk of hyponatremia due to excessive water intake (Noakes et al., 2005; Noakes, 2007).

In addition to the recommendations described previously, a new strategy known as carbohydrate mouth rinse (CMR) is being studied in short bouts of exercise ([greater than or equal to] 60 minutes). In this strategy, individuals do not ingest liquids during exercise, but only rinse their mouth with a carbohydrate solution for 5-10 seconds, after which it is expectorated (Thomas et al., 2016). The hypothesis is that carbohydrates would be detected by taste receptors, activating important brain regions related to motivation and motor control, and also improving performance without any ingestion of carbohydrate (Bortolotti et al., 2011; Carter et al., 2004; Jeukendrup, 2014). Carter et al. (2004) were the first to test this hypothesis and to demonstrate performance benefits, though subjects were tested after fasting for 4 hours, which may not be reproducible in practical situations. In addition, CMR was compared to rinsing with a placebo solution containing only water in their composition, which could directly influence the results, because subjects could have perceived the nature of the tested solution. Considering that individuals do not ingest liquids during exercise, its impact on hydration and performance of athletes, along with its effectiveness compared to strategies traditionally recommended are still unknown.

Therefore, the necessity to learn how different nutrition strategies would influence performance of athletes in short high-intensity exercises (

Methods

Participants

Eleven male trained cyclists were recruited to participate in the study. They had a training routine of at least 150 km for 5 hours a week and were heat acclimated, because they lived and trained at an average annual temperature of 28[degrees] C and average relative humidity of 83%. Exclusion criteria included smoking, obesity (BMI [greater than or equal to] 30 kg/[m.sup.2]), previous diagnosis of chronic diseases and musculoskeletal injuries within the last 6 months that could interfere with training routine. Participants were recruited via digital media and personal contact, in the Department of Physical Education of the Federal University of Rio Grande do Norte and in cycling teams of the city from April to December 2015. This study was approved by the University Human Research Ethics Committee (CAAE: 31747714.7.0000. 5568). All participants were informed about the procedures and signed the written informed consent. The number of participants included in the present study was calculated based on the study of Carter et al.(Carter et al., 2004), considering a test power of 90% and significance level of 5%. The protocol for this trial and supporting CONSORT checklist are available as supporting information.

Study design

Each subject attended the laboratory on five different occasions. In the first visit, subjects performed a body composition assessment (anthropometric technique) and evaluation of performance in a maximal exercise test. The second visit was a familiarization session on the 30 km cycle ergometer time trial, with specific instructions to experimental trials and without ingestion of fluids during exercise. Visits 3-5 consisted of controlled trials, in which participants completed time trial test at self-selected intensity and in a fed state. They were under random influence of the following interventions: CMR = carbohydrate mouth rinse; DWL = drinking to replace all weight loss; DAL = drinking "ad libitum". The order of interventions was randomized by drawing lots for each participant with a minimum of four days between tests. Participants were aware of the intervention selected only at the beginning of test, but they were blinded to the composition of solutions that were offered in cups of translucent coloration.

Anthropometric assessment

Weight and height from all subjects were determined by a portable digital scale coupled to a stadiometer with accuracy of 0.1 kg and 1.0 cm (Welmy[R], W 110 H, Brazil). Body Mass Index was calculated and nutritional status was classified according to the cut-off points defined by the World Health Organization (WHO, 2000). All measurements of skinfolds (triceps, subscapular, chest, biceps, iliac crest, abdominal, medial thigh and calf) were made on the right side of the body by using a compass with accuracy of 0.1 mm (Cescorf[R], Brazil). Identification of sites and measurements were in accordance with the International Society for the Advancement of Kinanthropometry (ISAK) standards. Skinfold measurement were used for calculation of body density using the generalized equation proposed by Jackson and Pollock (1978), and later converted to fat percentage, according to formula proposed by Siri (1961).

Maximal exercise test

Subjects performed a maximal exercise test on a cycle ergometer (Velotron, Racermate, Inc., Seattle, WA, USA) to determine the maximal oxygen uptake ([VO.sub.2max]) and heart rate (HRmax). The initial workload was 100W followed by 25W increments per minute until exhaustion. Subjects were instructed to maintain cadence [greater than or equal to] 80 rpm. The gas exchange breath-by-breath was recorded throughout the maximal exercise test (Quark--CPET, Cosmed, Roma, Italy). [VO.sub.2max] was considered as the highest mean value in 30s recorded during the test. Heart rate was recorded throughout the test using a Polar Monitoring System (Polar RS800cx, Kempele, Finland). All subjects achieved [greater than or equal to] 95% of age-predicted maximal HR (220--age) at the moment of volitional exhaustion. The appropriate seat position and handlebar height were determined and replicated for each subsequent visit.

Experimental trials

Before all trials, participants proceeded urine collection and weight measurement (light clothing and no shoes). They were equipped with a heart rate monitor and instructed to perform a 30 km time trial cycle ergometer (Velotron, Racermate, Inc., Seattle, WA, USA) with self-regulated pace in the shortest time possible, under three different nutritional strategies. The evaluation of physical performance was based on the total time to complete the 30 km time trial in each intervention. Heart rate was...

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