Effects of nitrate on the power-duration relationship for severe-intensity exercise

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.

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, ∼8.2 mmol·d nitrate) or a nitrate-depleted BR placebo (PL; 2 × 250 mL·d, ∼0.006 mmol·d 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'.

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.

Dietary nitrate supplementation improved endurance during severe-intensity exercise in recreationally active subjects without significantly increasing either the CP or the W'.