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.

Dietary nitrate supplementation enhances short but not longer duration running time-trial performance

“…It is therefore possible that elevated type II muscle Ca 2+ handling and muscle contractile function may have further contributed to the improved 1500 m performance observed in the present investigation. Furthermore, several recent studies have observed improvements in physiological functioning and exercise performance in situations where type II muscle recruitment is likely to be high (Breese et al 2013;Bailey et al 2015;Coggan et al 2015), which further supports the findings of this investigation.…”

“…These effects, which were reported in predominantly type II muscle, were accompanied by an increased muscle force production. Subsequent studies have confirmed the beneficial effect of NO 3 − on force production in humans (Haider and Folland 2014;Coggan et al 2015). It is therefore possible that elevated type II muscle Ca 2+ handling and muscle contractile function may have further contributed to the improved 1500 m performance observed in the present investigation.…”

“…Recent data from murine models suggest that NO 3 − supplementation elevates blood flow and oxygenation (Ferguson et al 2013(Ferguson et al , 2015, and increases calcium (Ca 2+ ) handling protein expression and force production (Hernandez et al 2012) in type II muscle only (for review, see Jones et al 2016). Therefore, the beneficial effects of NO 3 − supplementation might be restricted to, or most pronounced during, exercise where type II fibers are predominantly recruited (Breese et al 2013;Bailey et al 2015;Coggan et al 2015), such as during short duration exercise where a higher relative work rate can be adopted (Essén 1978;Sale 1987). Additionally, hypoxia and acidosis-cellular conditions particularly prevalent at higher work rates (Richardson et al 1995;Robergs et al 2004)-are known to enhance the reduction of NO 2 − into NO (Modin et al 2001;Cosby et al 2003;Castello et al 2006).…”

Dietary nitrate supplementation enhances high-intensity running performance in moderate normobaric hypoxia, independent of aerobic fitness

“…Further, there is evidence from murine model investigations that nitrate supplementation may enhance tissue blood flow [41,42] and muscle contractile function [9] preferentially in type II muscle fibres. It is therefore possible that nitrate supplementation is more effective during shorter more high-intensity exercise, during which these muscle fibres are more heavily recruited [9,[43][44][45]64], or else in individuals with greater distribution of type II muscle fibres [43]. The time-trial duration employed in this study (< 6 minutes) was considerably less than other investigations (~ 17 -48 minutes) which have not observed an ergogenic effect of nitrate supplementation in hypoxia [38][39][40], and may be important.…”

Inorganic nitrate supplementation improves muscle oxygenation, O2uptake kinetics, and exercise tolerance at high but not low pedal rates

“…Similarly, increased evoked contractile force has been observed in human skeletal muscle in vivo during low-frequency submaximal stimulation and over the initial stages of high-frequency maximal stimulation following NO 3 Ϫ supplementation (31). However, NO 3 Ϫ ingestion has been shown to increase human peak knee extensor torque at 360°/s, but not 90°/s, 180°/s, and 270°/s, in vivo (15). Collectively, these findings suggest that dietary NO 3 Ϫ supplementation enhances skeletal muscle contractile function, and that it might be particularly effective at augmenting contractility at higher contraction velocities.…”