Dietary nitrate supplementation enhances muscle contractile efficiency during knee-extensor exercise in humans.
The purpose of this study was to elucidate the mechanistic bases for the reported reduction in the O(2) cost of exercise following short-term dietary nitrate (NO(3)(-)) supplementation. In a randomized, double-blind, crossover study, seven men (aged 19-38 yr) consumed 500 ml/day of either nitrate-rich beet root juice (BR, 5.1 mmol of NO(3)(-)/day) or placebo (PL, with negligible nitrate content) for 6 consecutive days, and completed a series of low-intensity and high-intensity "step" exercise tests on the last 3 days for the determination of the muscle metabolic (using (31)P-MRS) and pulmonary oxygen uptake (Vo(2)) responses to exercise. On days 4-6, BR resulted in a significant increase in plasma [nitrite] (mean +/- SE, PL 231 +/- 76 vs. BR 547 +/- 55 nM; P < 0.05). During low-intensity exercise, BR attenuated the reduction in muscle phosphocreatine concentration ([PCr]; PL 8.1 +/- 1.2 vs. BR 5.2 +/- 0.8 mM; P < 0.05) and the increase in Vo(2) (PL 484 +/- 41 vs. BR 362 +/- 30 ml/min; P < 0.05). During high-intensity exercise, BR reduced the amplitudes of the [PCr] (PL 3.9 +/- 1.1 vs. BR 1.6 +/- 0.7 mM; P < 0.05) and Vo(2) (PL 209 +/- 30 vs. BR 100 +/- 26 ml/min; P < 0.05) slow components and improved time to exhaustion (PL 586 +/- 80 vs. BR 734 +/- 109 s; P < 0.01). The total ATP turnover rate was estimated to be less for both low-intensity (PL 296 +/- 58 vs. BR 192 +/- 38 microM/s; P < 0.05) and high-intensity (PL 607 +/- 65 vs. BR 436 +/- 43 microM/s; P < 0.05) exercise. Thus the reduced O(2) cost of exercise following dietary NO(3)(-) supplementation appears to be due to a reduced ATP cost of muscle force production. The reduced muscle metabolic perturbation with NO(3)(-) supplementation allowed high-intensity exercise to be tolerated for a greater period of time.
Bailey
Stephen J
SJ
School of Sport and Health Sciences, University of Exeter, Heavitree Rd., Exeter EX1 2LU, UK.
Fulford
Jonathan
J
Vanhatalo
Anni
A
Winyard
Paul G
PG
Blackwell
Jamie R
JR
DiMenna
Fred J
FJ
Wilkerson
Daryl P
DP
Benjamin
Nigel
N
Jones
Andrew M
AM
D000328:Adult; D027461:Beta vulgaris; D001628:Beverages; D019587:Dietary Supplements; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007717:Knee / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D053580:Muscle Strength / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000187:drug effects*; D009566:Nitrates / Q000008:administration & dosage*; D009573:Nitrites / Q000032:analysis; D010101:Oxygen Consumption / Q000187:drug effects; D010725:Phosphocreatine / Q000032:analysis; D012123:Pulmonary Ventilation / Q000187:drug effects; D055815:Young Adult
D009566:Nitrates; D009573:Nitrites; D010725:Phosphocreatine