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

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

5 ( 14 )  , p.e13340 , 2017-07 , Wiley
This study investigated the influence of dietary inorganic nitrate (NO3(-)) 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 (NO3(-))‐rich (BR; providing 8.4mmol (NO3(-))−∙day−1) and (NO3(-)) ‐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 ± 0.08Lmin(-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 (NO3(-))supplementation increased O2 diffusive conductance across locomotor muscles in association with improved (V˙O2) dynamics during heavy-intensity cycling transitions.

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