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Journal of Exercise Physiologyonline

August 2014 Volume 17 Number 4

Editor-in-Chief Tommy Boone, PhD, MBA Review Board Todd Astorino, PhD Julien Baker, PhD Steve Brock, PhD Lance Dalleck, PhD Eric Goulet, PhD Robert Gotshall, PhD Alexander Hutchison, PhD M. Knight-Maloney, PhD Len Kravitz, PhD James Laskin, PhD Yit Aun Lim, PhD Lonnie Lowery, PhD Derek Marks, PhD Cristine Mermier, PhD Robert Robergs, PhD Chantal Vella, PhD Dale Wagner, PhD Frank Wyatt, PhD Ben Zhou, PhD Official Research Journal of the American Society of

Exercise Physiologists

ISSN 1097-9751

Official Research Journal of the American Society of Exercise Physiologists

ISSN 1097-9751

JEPonline

Vitamin B6 and Maltodextrin Sport Drink Modify Glucose Levels of Elite Mountain Biking Athletes Irene Bronkhorst1; Luiz Silva1; Leandro Freitas1, Marcos Martins2, Hilana Martins2, Carlos Malfatti1, 1Laboratory of Biomedical Sciences/Department of Physical Education/ Midwest State University, Guarapuava, Brazil, 2Physical Education Post-Graduation Program/UFPR, Curitiba, Brazil

ABSTRACT Bronkhorst I, Silva L, Freitas L, Martins M, Martins H, Malfatti C. Vitamin B6 and Maltodextrin Sport Drink Modify Glucose Levels of Elite Mountain Biking Athletes. JEPonline 2014;17(4):113-121. The aim of this study was to analyze the effects of vitamin B6 and/or maltodextrin in pre- and post-exercise conditions and changes in performance and blood glucose (BG) levels in maximal test performed in laboratory on elite mountain biking (MTB) athletes. Eight male bikers [age, 28.4 10.6 yrs; body fat, 9.46 3.76%; VO2 max, 61.13 8.4 mLkg-1min-1] received supplementation drinks composed of carbohydrate (CHO) maltodextrin (1 gkg-1) and/or vitamin B6 (30 mgkg-1) or a placebo (juice light with 3.5 g of maltodextrin) in 500 ml of water. The subjects performed a maximal cycling test on a cycle ergometer at 60 revmin-1, starting at 50 W that was increased by 25 W every 3 min until exhaustion. Blood glucose was measured at rest, post-supplementation, and post-exercise testing. The comparisons between variables were made using analysis of variance (ANOVA) with post hoc Bonferroni test. A P

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INTRODUCTION Vitamin B6 is a collective term for a group of three related compounds, pyridoxine, pyridoxal, pyridoxamine, and their phosphorylated derivatives (30). Pyridoxal 5-phosphate (PLP) is an essential cofactor in all living systems and participates in catalysis by a wide diversity of enzymes including oxidoreductases, transferases, hydrolases, lyases, isomerases. decarboxylases, and cleavage enzymes used in transformations of amino acids (19,23). Pyridoxal 5-phosphate is the catalytically active form of vitamin B6. It is well established in numerous reports (6,13,16,18,21,22) that plasma PLP concentrations increase during submaximal exercise. Pyridoxal 5-phosphate is needed during exercise for gluconeogenesis and for glycogenolysis in which it serves as a cofactor for glycogen phosphorylase (21). In regards to skeletal muscle, the concentration of PLP can change during exercise due to need of carbohydrate consumption. Leklem and Hollenbeck (19) demonstrated that exercise of relatively long duration results in a significant increase in blood levels of PLP. They suggested that exercise is a form of acute energy deficit that initiates the release of vitamin B6 from muscle. Under this hypothesis the coenzyme would be needed in the liver for aminotransferase reactions, providing amino acid carbon skeletons for gluconeogenesis (17). Carbohydrate (CHO) supplementation pre-exercise, during exercise, and post-exercise has been shown to increase the amount of work that can be performed (4,8,32) as well as increase the duration of aerobic exercise (8,33). The increase in blood glucose (BG) associated with CHO supplementation is suggested to improve aerobic performance through reduction of muscle glycogen use (5,15,28,33) or through the use of BG as a predominant fuel source as glycogen becomes depleted (5,12,25). The type of CHO supplementation is very important. It has been suggested that because of the lower osmolalities, glucose polymer solutions (such as maltodextrin) are preferable to isocaloric glucose solutions as a source of ingested CHO before and during exercise (16). Indeed, several studies have shown that the rates of gastric emptying for glucose polymer solutions are faster than those of isocaloric glucose solutions (9,24). In addition, it has been suggested that glucose feedings (75 g of glucose solutions) 30 to 45 min before exercise in cyclists might impair exercise performance by causing a sudden drop in BG and an accompanying acceleration of muscle glycogen oxidation. Relatively little has been published concerning the effects of exercise on vitamin B6 metabolism and maltodextrin supplementation. The purpose of this study was to investigate the effect of consuming vitamin B6 and/or maltodextrin in pre-exercise and post-exercise conditions on exercise performance and blood glucose levels in athletes.

METHODS Subjects Eight elite athletic mountain bikers participated in double-blind study. Resting anthropological and physiological characteristics of the subjects are presented in Table 1. An informed consent was obtained from each subject in accordance with Resolution 196/96 of the National Council of Health in Brazil, which was approved by local Ethics Committee.

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Table 1. Resting Anthropological and Physiological Measures of the Subjects. Characteristics

N = 8

Age (yrs) 28.4 10.6

Body Fat (%) 9.46 3.76

SBP (mmHg) 120.7 11

DBP (mmHg) 76.7 10.3

HR (beatsmin-1) 75.3 8

Fasting Glucose (mgdL-1) 82.6 7

Maximal Power Output (W) 280.8 12.9

WVT (W) 150.5 8.7 Data are means SE. Abbreviations: SBP, systolic blood pressure; DBP, diastolic blood pressure; WVT, power output at ventilatory threshold; HR, heart rate

Procedures Prior to the prescription of exercise and treatments (1 wk before), the subjects was evaluated in the laboratory to obtain resting physiological and anthropometrical measures. Body mass and height were measured using anthropometrical devices (Welmy Corporation, EUA). The subjects body fat was measured by means of the skinfold technique (14,29), using a skinfold caliper (Cescorf Corporation, EUA). Blood pressure was measured with a pressure device (Protec). The subjects had previously fasted for 6 hrs before the measurements were taken. At 30 min prior to each test, the subjects received supplementation drinks composed of maltodextrin (1 gkg-1) and/or vitamin B6 (30 mgkg-1) or a placebo (juice light with 3.5 g of CHO) in 500 ml of water. The subjects were not to exercise 24 hrs prior to the laboratory tests. They were informed that the test consisted of a maximal cycling effort on a cycle ergometer at 60 revmin-1 at 50 W. The workload would increase 25 W every 3 min until exhaustion with each supplementation (cycle ergometer Biotec 1800-CEFISE) to determined the influence, if any, on maximal heart rate (HR max), maximal power output (W max), maximal oxygen uptake (VO2 max), and ventilatory threshold (VT). Ventilation threshold (VT) was determined as a plot of ventilation (VE) versus oxygen consumption (VO2), as described previously (27). Two linear regression lines were fit to the lower and upper portions of the VE versus VO2 curve before and after the break points, respectively. The intersection of these two lines was defined as VT. Open circuit spirometry was used to analyze the gas exchange data using the Parvo-Medics TrueOne 2400 Metabolic Measurement System (Sandy, Utah, USA). Oxygen and carbon dioxide were analyzed through a sampling line after the gases passed through a heated pneumotach and mixing chamber. The data were averaged over 15-sec intervals. The highest average VO2 value during the test was recorded as the VO2 max if it coincided with at least two of the following criteria: (a) a plateau

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in HR or HR values within 10% of the age-predicted HR max; (b) a plateau in VO2 (defined by an increase of no more than 150 mLmin-1); and/or (c) an respiratory exchange ratio of 1.15 or greater. Heart rate (HR) was monitored every 5 sec during the test (Polar Team System). Exhaustion was defined as the point when the subject was no longer capable of maintaining the pedaling rate of 60 revmin-1. The highest VO2 value obtained from the last minute of exercise was considered the VO2 max (7). Capillary blood samples were used to determine the glucose concentrations using a digital glucosimeter (ACCU CHEK Performa, Roche), and ACCU-CHEK Multiclix lancetador, with grade 5 on the distal phalange of the right hand 3rd finger at rest (basal), 20 min after maltodextrin, vitamin B6 or placebo use and immediately at the end of maximal cycle test.

Statistical Analyses The data are presented as means SE. Statistical analysis included the use of a one-way analysis of variance (ANOVA) with statistical significance set at P

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During the cycle ergometer test, VT was significantly lower in the vitamin B6 group versus the CHO group and even more so in the vitamin B6 + CHO group versus the CHO and placebo groups (P

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During exercise, the body depends on the production of glucose from the liver to maintain normal glucose levels in the plasma (20). Therefore, supplementation seems to contribute to more vitamin B6 storage in the muscle and its subsequent release during exercise (22). Note in Figure 1, the plasma glucose levels are higher for maltodextrin and maltodextrin supplementation associated with vitamin B6 compared to the placebo and vitamin B6 alone (21 mgdL-1; 24%; P

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