RESUMEN
PURPOSE: We tested the hypothesis that carbohydrate ingestion during exercise improves time trial (TT) performance and that this carbohydrate-induced improvement is greater when carbohydrates are ingested during exercise in a fasted rather than a fed state. METHODS: Nine males performed 105 minutes of constant-load exercise (50% of the difference between the first and second lactate thresholds), followed by a 10-km cycling TT. Exercise started at 9 am, 3 hours after either breakfast (FED, 824 kcal, 67% carbohydrate) or a 15-hour overnight fast (FAST). Before exercise, after every 15 minutes of exercise and at 5 km of the TT, participants ingested 2 mL kg-1 body mass of a non-caloric sweetened solution containing either carbohydrate (8% of maltodextrin, CHO) or placebo (0% carbohydrate, PLA). RESULTS: Irrespective of the fasting state, when carbohydrate was ingested during exercise, the rating of perceived exertion (RPE) was lower throughout the constant-load exercise, while the plasma glucose concentration and carbohydrate oxidation were higher during the last stages of the constant-load exercise (P < 0.05). Consequently, TT performance was faster when carbohydrate was ingested during exercise (18.5 ± 0.3 and 18.7 ± 0.4 minutes for the FEDCHO and FASTCHO conditions, respectively) than when the placebo was ingested during exercise (20.2 ± 0.8 and 21.7 ± 1.4 minutes for the FEDPLA and FASTPLA conditions, respectively), regardless of fasting. CONCLUSION: These findings indicate that even when breakfast is provided before exercise, carbohydrate ingestion during exercise is still beneficial for exercise performance. However, ingesting carbohydrate during exercise can overcome a lack of breakfast.
Asunto(s)
Rendimiento Atlético/fisiología , Ciclismo/fisiología , Carbohidratos de la Dieta/administración & dosificación , Ayuno , Fenómenos Fisiológicos en la Nutrición Deportiva , Adulto , Glucemia/análisis , Metabolismo de los Hidratos de Carbono , Método Doble Ciego , Humanos , Masculino , Esfuerzo Físico , Adulto JovenRESUMEN
While nitrate supplementation influences oxygen uptake (VÌO2) response to exercise, this effect may be intensity dependent. The purpose of this study was to investigate the effect of acute nitrate supplementation on VÌO2 response during different exercise intensity domains in humans. Eleven men ingested 10 mg·kg-1 body mass (8.76 ± 1.35 mmol) of sodium nitrate or sodium chloride (placebo) 2.5 h before cycling at moderate (90% of gas exchange threshold; GET), heavy (GET + 40% of the difference between GET and peak oxygen uptake (VÌO2peak), Δ 40) or severe (GET + 80% of the difference between GET and VÌO2peak, Δ 80) exercise intensities. Volunteers performed exercise for 10 min (moderate), 15 min (heavy) or until exhaustion (severe). Acute nitrate supplementation had no effect on any VÌO2 response parameters during moderate and severe exercise intensities. However, the VÌO2 slow amplitude (nitrate: 0.93 ± 0.36 L·min-1 vs. placebo: 1.13 ± 0.59 L·min-1, p = 0.04) and VÌO2 slow gain (nitrate: 5.81 ± 2.37 mL·min-1·W-1 vs. placebo: 7.09 ± 3.67 mL·min-1·W-1, p = 0.04) were significantly lower in nitrate than in placebo during the heavy exercise intensity. There was no effect of nitrate on plasma lactate during any exercise intensity (p > 0.05). Time to exhaustion during the severe exercise intensity was also not affected by nitrate (p > 0.05). In conclusion, acute nitrate supplementation reduced the slow component of VÌO2 only when performing heavy-intensity exercise, which might indicate an intensity-dependent effect of nitrate on VÌO2 response.