Dietary nitrate supplementation does not alter V̇O2p gain during ramp incremental cycling exercise

Abstract

In a previous study 15 days of dietary nitrate/nitrite (NO3−/NO2−) supplementation was associated with a lower V̇O2p gain (ΔV̇O2p/ΔPower Output; PO) in the moderate (MOD) intensity exercise domain and a higher V̇O2p gain for exercise above lactate threshold (θL) 1. It remains unclear how V̇O2p gain is affected within the heavy‐ (HVY; supra‐θL, infra‐respiratory compensation point [RCP]) and very heavy‐intensity (VH; supra‐RCP) exercise domains during ramp incremental (RI) exercise to the limit of tolerance (LoT).PURPOSETo investigate the role of 20 days of dietary NO3−/NO2− supplementation on V̇O2p gain during a ramp incremental‐sprint (RISP) exercise protocol.METHODSUsing a double‐blind, block randomised, repeated measures design, 8 healthy, active males (age 24 ± 2 yr [mean ± SD]; V̇O2p‐max 44 ± 6 mL O2·kg−1·min−1) consumed NO3−‐rich (N+; 12.8 mmol NO3−) or ‐depleted (PL; 0.08 mmol NO3−) beetroot juice per day for 20 days. Prior to supplementation participants completed a RISP test consisting of 6 min baseline leg cycling at 25 W, RI exercise (25 W·min−1) to the LoT, and, after 3 min resting recovery, a 3 min variable PO sprint protocol. V̇O2p was measured breath‐by‐breath. No exercise was conducted on days 1–5 of supplementation. Constant‐load VH (6 bouts with each bout lasting 3–18 min) or MOD (1 bout lasting 18 min) were performed on alternate days during days 6–18. On day 20, participants completed a final RISP test. After a 14‐day washout period the protocol was repeated with participants consuming the other supplement condition.RESULTSPre‐supplement baseline plasma [NO3−] and [NO2−] were not different (P > 0.05) between N+ and PL, but were elevated (P < 0.05) on days 6, 14, and 20 of N+ supplementation (NO3−: 32 ± 14 μM at BSL to 325 ± 143 μM; NO2−: 119 ± 130 nM at BSL to 245 ± 155 nM). There were no differences (P > 0.05) between NO3−‐rich and ‐depleted conditions in V̇O2p gain within the MOD (N+, 9.3 ± 1.2 vs PL, 9.4 ± 1.2 mL O2·min−1·W−1), HVY (N+, 9.3 ± 0.9 vs PL, 9.1 ± 1.2 mL O2·min−1·W−1), VH (N+, 9.7 ± 2.2 vs PL, 9.1 ± 1.9 mL O2·min−1·W−1; P = 0.173) domains or whole ramp (N+, 9.6 ± 0.7 vs PL, 9.2 ± 1.0 mL O2·min−1·W−1; P = 0.119). No differences were found in V̇O2p at θL (N+, 2.10 ± 0.50 vs PL, 2.04 ± 0.52 L·min−1) or RCP (N+, 3.06 ± 0.63 vs PL, 3.00 ± 0.67 L·min−1), or between V̇O2p‐peak measured at end‐ramp or the final 20s of the sprint between N+ and PL and within N+ and PL (End‐ramp: N+, 3.67 ± 0.69 vs PL, 3.51 ± 0.73 mL·min−1 [P = 0.101]; Sprint: N+, 3.70 ± 0.66 vs PL, 3.57 ± 0.67 mL·min−1 [P = 0.08]).CONCLUSIONDespite elevated plasma [NO3−] and [NO2−], V̇O2p gains were unaffected in the MOD, HVY, or VH intensity domains assessed throughout RI exercise. These data suggest O2 utilization efficiency in contracting quadriceps muscle is not impacted by elevated plasma [NO3−] and [NO2−], at least within the conditions of the current study.Support or Funding InformationFunded by NSERC and James White Drinks