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

This study investigated the influence of dietary inorganic nitrate (NO (3) (−)) supplementation on pulmonary O(2) uptake ([Formula: see text] O(2)) 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 [Formula: see text] O(2) 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 [Formula: see text] O(2) 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 [Formula: see text] O(2) 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 O(2) diffusive conductance across locomotor muscles in association with improved [Formula: see text] O(2) dynamics during heavy‐intensity cycling transitions.