Ingestão de carboidratos e proteína em cápsulas durante o exercício nocalor: efeitos sobre o desempenho físico de atletas no estado alimentado

Abstract

It has been suggested that exercise performance in the heat might be limited by centralmechanisms. One of the proposed mechanisms associates increased central serotonergic activityto the onset of fatigue. Different nutritional strategies have been used in an attempt to decreasecentral serotonergic activity thus improving performance. The purpose of the present study wasto verify whether carbohydrates (CHO) or protein (PTN) would improve performance in the heat(31ºC e 50% RH) when subjects were previously fed. Ten well-trained male subjects (26 ± 1anos; 64.45 ± 2.42 kg; 1,7 ± 0,3 m; 5.38 ± 0.52 % body fat; peak power output 323 ± 13 W; heartrate maxima 190 ± 2 bpm VO2max.70.7 ± 2.8 mLO2.kg-1.min-1) volunteered to took part in thestudy. The participants performed 60-km self-paced bicycle rides, interspersed with 1-km all-outsprints at the 14th, 29th, 44ndand 60th km, in an environmental chamber. They were subjectedrandomly to three different treatments, during which they ingested: only water (H2O); water +capsules containing whey-protein isolate (PTNc, 3,9%); water + capsules containingcarbohydrates (CHOc, 6%). The last two treatments were run on a double-blinded protocol.Administration of the treatments occurred at the 5th, 15th, 30 th, 45 th and 55 th km. Blood sampleswere collected through a catheter from a superficial forearm vein at the pre-exercise period and atthe 9th, 24th, 39th, 54th and 60th km. The data were analyzed using a Latin Square Design and aGeneral Linear Model, followed by Tukey LSD test when appropriate. No differences inperformance times for both 60 km and 1 km sprints were observed between the three treatments.Free fatty acids, tryptophan (TRP), urea, prolactin, rate of perceived exertion, heart rate, coretemperature and lactate analyzed over time were also similar during all treatments. Plasmaglucose and serum insulin were higher in CHOc. Plasma branched chain amino acids (BCAA)were higher in PTNc. The TRP/BCAA ratio was reduced in PTNc. The ingestion ofcarbohydrates or protein in capsules did not improve exercise performance in the heat, despitechanges in some of the peripheral factors proposed in Central Fatigue Hypothesis.