RESUMO
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.
Assuntos
Exercício Físico , Nitratos/administração & dosagem , Consumo de Oxigênio/efeitos dos fármacos , Adulto , Índice de Massa Corporal , Estudos Cross-Over , Suplementos Nutricionais , Método Duplo-Cego , Humanos , Ácido Láctico/sangue , Masculino , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/fisiologia , Cloreto de Sódio/administração & dosagem , Inquéritos e Questionários , Adulto JovemRESUMO
PURPOSE: To examine the influence of two different fast-start pacing strategies on performance and oxygen consumption (VO2) during cycle ergometer time trials lasting â¼5 min. METHODS: Eight trained male cyclists performed four cycle ergometer time trials whereby the total work completed (113 ± 11.5 kJ; mean ± SD) was identical to the better of two 5-min self-paced familiarization trials. During the performance trials, initial power output was manipulated to induce either an all-out or a fast start. Power output during the first 60 s of the fast-start trial was maintained at 471.0 ± 48.0 W, whereas the all-out start approximated a maximal starting effort for the first 15 s (mean power: 753.6 ± 76.5 W) followed by 45 s at a constant power output (376.8 ± 38.5 W). Irrespective of starting strategy, power output was controlled so that participants would complete the first quarter of the trial (28.3 ± 2.9 kJ) in 60 s. Participants performed two trials using each condition, with their fastest time trial compared. RESULTS: Performance time was significantly faster when cyclists adopted the all-out start (4 min 48 s ± 8 s) compared with the fast start (4 min 51 s ± 8 s; P < 0.05). The first-quarter VO2 during the all-out start trial (3.4 ± 0.4 L·min(-1)) was significantly higher than during the fast-start trial (3.1 ± 0.4 L·min(-1); P < 0.05). After removal of an outlier, the percentage increase in first-quarter VO2 was significantly correlated (r = -0.86, P < 0.05) with the relative difference in finishing time. CONCLUSIONS: An all-out start produces superior middle distance cycling performance when compared with a fast start. The improvement in performance may be due to a faster VO2 response rather than time saved due to a rapid acceleration.