Dynamic arterial baroreflex function during high intensity exercise in humans: insights into sympathetic control

The stability of arterial blood gas tensions and pH during steady-state moderate exercise has suggested an important humoral element of ventilatory control in humans. However, the involvement of central and peripheral chemoreflexes in this humoral control remains controversial. This reflects, in large part, technical and interpretational limitations inherent in currently used estimators of chemoreflexes "sensitivity." Evidence suggests that the central chemoreceptors (a) contribute little during moderate exercise, given the relative stability of cerebrospinal pH, (b) constrain the hyperpnea of high-intensity exercise, consequent to the respiratory compensation for the metabolic acidemia, and (c) may play a role in the respiratory compensation during chronic metabolic acidemia. In contrast, the peripheral chemoreceptors appear to (a) exert considerable influence on ventilatory kinetics in moderate exercise, but are less important in the steady state, and (b) induce much of the respiratory compensation of high-intensity exercise. Key words: medullary chemoreceptors, carotid chemoreceptors, hyperoxia, ventilatory dynamics, metabolic acidemia

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Dietary nitrate supplementation reduces the O2cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans

Journal of Applied Physiology ◽

10.1152/japplphysiol.00722.2009 ◽

2009 ◽

Vol 107 (4) ◽

pp. 1144-1155 ◽

Cited By ~ 424

Author(s):

Stephen J. Bailey ◽

Paul Winyard ◽

Anni Vanhatalo ◽

Jamie R. Blackwell ◽

Fred J. DiMenna ◽

...

Keyword(s):

High Intensity ◽

Submaximal Exercise ◽

High Intensity Exercise ◽

Moderate Intensity ◽

Nitrate Content ◽

Time To Exhaustion ◽

Moderate Exercise ◽

Dietary Nitrate ◽

Nitrate Supplementation ◽

Exercise In Humans

Pharmacological sodium nitrate supplementation has been reported to reduce the O2cost of submaximal exercise in humans. In this study, we hypothesized that dietary supplementation with inorganic nitrate in the form of beetroot juice (BR) would reduce the O2cost of submaximal exercise and enhance the tolerance to high-intensity exercise. In a double-blind, placebo (PL)-controlled, crossover study, eight men (aged 19–38 yr) consumed 500 ml/day of either BR (containing 11.2 ± 0.6 mM of nitrate) or blackcurrant cordial (as a PL, with negligible nitrate content) for 6 consecutive days and completed a series of “step” moderate-intensity and severe-intensity exercise tests on the last 3 days. On days 4–6, plasma nitrite concentration was significantly greater following dietary nitrate supplementation compared with PL (BR: 273 ± 44 vs. PL: 140 ± 50 nM; P < 0.05), and systolic blood pressure was significantly reduced (BR: 124 ± 2 vs. PL: 132 ± 5 mmHg; P < 0.01). During moderate exercise, nitrate supplementation reduced muscle fractional O2extraction (as estimated using near-infrared spectroscopy). The gain of the increase in pulmonary O2uptake following the onset of moderate exercise was reduced by 19% in the BR condition (BR: 8.6 ± 0.7 vs. PL: 10.8 ± 1.6 ml·min−1·W−1; P < 0.05). During severe exercise, the O2uptake slow component was reduced (BR: 0.57 ± 0.20 vs. PL: 0.74 ± 0.24 l/min; P < 0.05), and the time-to-exhaustion was extended (BR: 675 ± 203 vs. PL: 583 ± 145 s; P < 0.05). The reduced O2cost of exercise following increased dietary nitrate intake has important implications for our understanding of the factors that regulate mitochondrial respiration and muscle contractile energetics in humans.

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