Purpose: The power asymptote (critical power [CP]) and curvature constant (W′) of the power–duration relationship dictate the tolerance to severe-intensity exercise. We tested the hypothesis that dietary nitrate supplementation would increase the CP and/or the W′ during cycling exercise.
Methods: In a double-blind, randomized, crossover study, nine recreationally active male subjects supplemented their diet with either nitrate-rich concentrated beetroot juice (BR; 2 × 250 mL·d−1, ∼8.2 mmol·d−1 nitrate) or a nitrate-depleted BR placebo (PL; 2 × 250 mL·d−1, ∼0.006 mmol·d−1 nitrate). In each condition, the subjects completed four separate severe-intensity exercise bouts to exhaustion at 60% of the difference between the gas exchange threshold and the peak power attained during incremental exercise (60% Δ), 70% Δ, 80% Δ, and 100% peak power, and the results were used to establish CP and W′.
Results: Nitrate supplementation improved exercise tolerance during exercise at 60% Δ (BR, 696 ± 120 vs PL, 593 ± 68 s; P < 0.05), 70% Δ (BR, 452 ± 106 vs PL, 390 ± 86 s; P < 0.05), and 80% Δ (BR, 294 ± 50 vs PL, 263 ± 50 s; P < 0.05) but not 100% peak power (BR, 182 ± 37 vs PL, 166 ± 26 s; P = 0.10). Neither CP (BR, 221 ± 27 vs PL, 218 ± 26 W) nor W′ (BR, 19.3 ± 4.6 vs PL, 17.8 ± 3 kJ) were significantly altered by BR.
Conclusion: Dietary nitrate supplementation improved endurance during severe-intensity exercise in recreationally active subjects without significantly increasing either the CP or the W′.
Sport and Health Sciences, College of Life and Environmental Sciences, St. Luke’s Campus, University of Exeter, Heavitree Road, Exeter, UNITED KINGDOM
Address for correspondence: Andrew M. Jones, Ph.D., Professor of Applied Physiology, Sport and Health Sciences, St. Luke’s Campus, University of Exeter, Exeter EX1 2LU, United Kingdom; E-mail: firstname.lastname@example.org.
Submitted for publication December 2012.
Accepted for publication February 2013.