Abstract
<jats:p>We tested the hypothesis that the time constants (τ) of postexercise T2* MRI signal intensity (an index of O<jats:sub>2</jats:sub>delivery) and muscle [PCr] (an index of metabolic perturbation, measured by<jats:sup>31</jats:sup>P-MRS) in hypoxia would be accelerated after dietary nitrate (NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>) supplementation. In a double-blind crossover design, eight moderately trained subjects underwent 5 days of NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>(beetroot juice, BR; 8.2 mmol/day NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>) and placebo (PL; 0.003 mmol/day NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>) supplementation in four conditions: normoxic PL (N-PL), hypoxic PL (H-PL; 13% O<jats:sub>2</jats:sub>), normoxic NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>(N-BR), and hypoxic NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>(H-BR). The single-leg knee-extension protocol consisted of 10 min of steady-state exercise and 24 s of high-intensity exercise. The [PCr] recovery τ was greater in H-PL (30 ± 4 s) than H-BR (22 ± 4 s), N-PL (24 ± 4 s) and N-BR (22 ± 4 s) ( P < 0.05) and the maximal rate of mitochondrial ATP resynthesis (Q<jats:sub>max</jats:sub>) was lower in the H-PL (1.12 ± 0.16 mM/s) compared with H-BR (1.35 ± 0.26 mM/s), N-PL (1.47 ± 0.28 mM/s), and N-BR (1.40 ± 0.21 mM/s) ( P < 0.05). The τ of postexercise T2* signal intensity was greater in H-PL (47 ± 14 s) than H-BR (32 ± 10 s), N-PL (38 ± 9 s), and N-BR (27 ± 6 s) ( P < 0.05). The postexercise [PCr] and T2* recovery τ were correlated in hypoxia ( r = 0.60; P < 0.05), but not in normoxia ( r = 0.28; P > 0.05). These findings suggest that the NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>-NO<jats:sub>2</jats:sub><jats:sup>−</jats:sup>-NO pathway is a significant modulator of muscle energetics and O<jats:sub>2</jats:sub>delivery during hypoxic exercise and subsequent recovery.</jats:p>
Original language | English |
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Pages (from-to) | 1460-1470 |
Number of pages | 0 |
Journal | Journal of Applied Physiology |
Volume | 117 |
Issue number | 12 |
DOIs | |
Publication status | Published - 15 Dec 2014 |