Effect of acute dietary nitrate intake on maximal knee extensor speed and power in healthy men and women

Abstract

Nitric oxide (NO) has been demonstrated to enhance the maximal shortening velocity and maximal power of rodent muscle. Dietary nitrate (NO3(-)) intake has been demonstrated to increase NO bioavailability in humans. We therefore hypothesized that acute dietary NO3(-) intake (in the form of a concentrated beetroot juice (BRJ) supplement) would improve muscle speed and power in humans. To test this hypothesis, healthy men and women (n = 12; age = 22-50 y) were studied using a randomized, double-blind, placebo-controlled crossover design. After an overnight fast, subjects ingested 140 mL of BRJ either containing or devoid of 11.2 mmol of NO3(-). After 2 h, knee extensor contractile function was assessed using a Biodex 4 isokinetic dynamometer. Breath NO levels were also measured periodically using a Niox Mino analyzer as a biomarker of whole-body NO production. No significant changes in breath NO were observed in the placebo trial, whereas breath NO rose by 61% (P < 0.001; effect size = 1.19) after dietary NO3(-) intake. This was accompanied by a 4% (P < 0.01; effect size = 0.74) increase in peak knee extensor power at the highest angular velocity tested (i.e., 6.28 rad/s). Calculated maximal knee extensor power was therefore greater (i.e., 7.90 ± 0.59 vs. 7.44 ± 0.53 W/kg; P < 0.05; effect size = 0.63) after dietary NO3(-) intake, as was the calculated maximal velocity (i.e., 14.5 ± 0.9 vs. 13.1 ± 0.8 rad/s; P < 0.05; effect size = 0.67). No differences in muscle function were observed during 50 consecutive knee extensions performed at 3.14 rad/s. We conclude that acute dietary NO3(-) intake increases whole-body NO production and muscle speed and power in healthy men and women.

Keywords: Dietary nitrate; Humans; Isokinetic; Muscle power; Nitric oxide.

Copyright © 2014 Elsevier Inc. All rights reserved.

Figures

Figure 1

Calculation of maximal knee extensor velocity (Vmax) and power (Pmax) for a representative subject. Open circles and dashed line, placebo trial. Closed circles and solid line, NO3- trial.

Figure 2

Effect of acute dietary NO3- intake on breath NO levels. Open bars, placebo trial. Closed bars, NO3- trial. Values are mean ± S.E. for n=12. NO3- trial significantly higher than placebo trial at same time point: ‡P<0.001.

Figure 3

Effect of acute dietary NO3- intake on estimated maximal knee extensor velocity (Vmax; top panel) and power velocity (Pmax; bottom panel). The open bars and closed bars indicate the mean (± S.E.) values for the placebo and NO3- trials, respectively, whereas the squares and circles illustrate the responses of individual male and female subjects, respectively. NO3- trial significantly higher than placebo trial: *P<0.05.