The effect of dietary nitrate supplementation on the spatial heterogeneity of quadriceps deoxygenation during heavy-intensity cycling.

Brynmor C. Breese,Andrew M. Jones,Narihiko Kondo,Tatsuro Amano,Shunsaku Koga,Dai Okushima,Stephen J. Bailey,David C. Poole

doi:10.14814/phy2.13340

Abstract

This study investigated the influence of dietary inorganic nitrate (NO 3 −) supplementation on pulmonary O2 uptake (V˙O2) and muscle deoxyhemoglobin/myoglobin (i.e. deoxy [Hb + Mb]) kinetics during submaximal cycling exercise. In a randomized, placebo‐controlled, cross‐over study, eight healthy and physically active male subjects completed two step cycle tests at a work rate equivalent to 50% of the difference between the gas exchange threshold and peak V˙O2 over separate 4‐day supplementation periods with NO 3 −‐rich (BR; providing 8.4 mmol NO 3 −∙day−1) and NO 3 −‐depleted (placebo; PLA) beetroot juice. Pulmonary V˙O2 was measured breath‐by‐breath and time‐resolved near‐infrared spectroscopy was utilized to quantify absolute deoxy [Hb + Mb] and total [Hb + Mb] within the rectus femoris, vastus lateralis, and vastus medialis. There were no significant differences (P > 0.05) in the primary deoxy [Hb + Mb] mean response time or amplitude between the PLA and BR trials at each muscle site. BR significantly increased the mean (three‐site) end‐exercise deoxy [Hb + Mb] (PLA: 91 ± 9 vs. BR: 95 ± 12 μmol/L, P < 0.05), with a tendency to increase the mean (three‐site) area under the curve for total [Hb + Mb] responses (PLA: 3650 ± 1188 vs. BR: 4467 ± 1315 μmol/L sec−1, P = 0.08). The V˙O2 slow component reduction after BR supplementation (PLA: 0.27 ± 0.07 vs. BR: 0.23 ± 0.08 L min−1, P = 0.07) correlated inversely with the mean increases in deoxy [Hb + Mb] and total [Hb + Mb] across the three muscle regions (r 2 = 0.62 and 0.66, P < 0.05). Dietary NO 3 − supplementation increased O2 diffusive conductance across locomotor muscles in association with improved V˙O2 dynamics during heavy‐intensity cycling transitions.

Highlights

Nitric oxide (NO) is a gaseous signaling molecule widely believed to play a crucial role in regulating vascular function and mitochondrial respiration (Brown 2001; Moncada and Higgs 2006)
Using multi-channel TRS-NIRS, this study investigated the effect of NO3-rich BR supplementation on absolute deoxy [Hb + Mb] and total [Hb + Mb] responses within the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) during heavy-intensity step cycling
Treatment does not alter the spatial heterogeneity of the dynamic balance between muscle O2 delivery relative to O2 utilization during heavy submaximal exercise

Summary

Introduction

Nitric oxide (NO) is a gaseous signaling molecule widely believed to play a crucial role in regulating vascular function and mitochondrial respiration (Brown 2001; Moncada and Higgs 2006). The most recognized pathway for NO production is the five-electron oxidation of L-arginine in a reaction catalyzed by the nitric oxide synthase (NOS) enzymes (Bredt et al 1991). An alternative O2-independent pathway has been identified where NO is produced from the stepwise reduction in inorganic nitrate (NO3) to nitrite (NO2) and subsequently NO (Lundberg and Weitzberg 2009). Previous studies have reported that dietary supplementation with sodium nitrate or NO3-rich beetroot juice (BR) elevates plasma [NO2] The Physiological Society and the American Physiological Society.

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