Dietary nitrate-induced increases in human muscle power: high versus low responders

Abstract

Maximal neuromuscular power is an important determinant of athletic performance and also quality of life, independence, and perhaps even mortality in patient populations. We have shown that dietary nitrate (NO 3 −), a source of nitric oxide (NO), improves muscle power in some, but not all, subjects. The present investigation was designed to identify factors contributing to this interindividual variability. Healthy men (n = 13) and women (n = 7) 22–79 year of age and weighing 52.1–114.9 kg were studied using a randomized, double‐blind, placebo‐controlled, crossover design. Subjects were tested 2 h after ingesting beetroot juice (BRJ) either containing or devoid of 12.3 ± 0.8 mmol of NO 3 −. Plasma NO 3 − and nitrite (NO 2 −) were measured as indicators of NO bioavailability and maximal knee extensor speed (V max), power (P max), and fatigability were determined via isokinetic dynamometry. On average, dietary NO 3 − increased (P < 0.05) P max by 4.4 ± 8.1%. Individual changes, however, ranged from −9.6 to +26.8%. This interindividual variability was not significantly correlated with age, body mass (inverse of NO 3 − dose per kg), body mass index (surrogate for body composition) or placebo trial V max or fatigue index (in vivo indicators of muscle fiber type distribution). In contrast, the relative increase in Pmax was significantly correlated (r = 0.60; P < 0.01) with the relative increase in plasma NO 2 − concentration. In multivariable analysis female sex also tended (P = 0.08) to be associated with a greater increase in Pmax. We conclude that the magnitude of the dietary NO 3 −‐induced increase in muscle power is dependent upon the magnitude of the resulting increase in plasma NO 2 − and possibly female sex.

A single dose of dietary nitrate increases maximal muscle speed and power in healthy older men and women

“…The purpose of the present study was to test the hypothesis that acute dietary NO3supplementation would improve muscle speed and power in healthy older men and women. In keeping with our previous studies (21)(22)(23)(24), we found that acute NO3ingestion increased Vmax and Pmax in older subjects by ~11 and ~4%, respectively. Although modest in size, the potential clinical significance of these changes is tremendous.…”

“…Their baseline breath NO levels, for example, were comparable to those we have found previously in younger subjects (21,22). Their baseline plasma NO3and NO2concentrations were also similar to those we have measured previously (22).…”

“…Their baseline breath NO levels, for example, were comparable to those we have found previously in younger subjects (21,22). Their baseline plasma NO3and NO2concentrations were also similar to those we have measured previously (22). Additional studies will therefore be required to determine whether dietary NO3is even more effective at enhancing muscle contractile function in older men and women in whom NO bioavailability is more clearly reduced (and/or in those who are frail).…”

“…Although the dietary NO3 --induced in muscle function observed in the present are likely to be highly clinically significant, they are in fact similar in magnitude to those we have previously found for healthy young and middle-aged subjects (21,22). This observation runs counter to our hypothesis that older subjects would benefit more from dietary NO3 -.…”

“…We have previously demonstrated that NO3supplementation increases muscle speed and power in healthy younger and middle-aged men and women (21,22), athletes (23), and patients with heart failure (HF) (24). However, it cannot simply be assumed that dietary NO3will be equally efficacious in older individuals.…”