Inorganic nitrate supplementation improves muscle oxygenation, O2 uptake kinetics and exercise tolerance at high but not low pedal rates
Bailey, Stephen J.
Varnham, Richard L.
DiMenna, Fred J.
Breese, Brynmor C.
Jones, Andrew M.
American Physiological Society
We tested the hypothesis that inorganic nitrate (NO3-) supplementation would improve muscle oxygenation, pulmonary O2 uptake (VO2) kinetics and exercise tolerance (Tlim) to a greater extent when cycling at high compared low pedal rates. In a randomized, placebo-controlled, cross-over study, seven subjects (mean ± SD, age 21 ± 2 yr, body mass 86 ± 10 kg) completed severe-intensity step cycle tests at pedal cadences of 35 rpm and 115 rpm during separate 9 day supplementation periods with NO3--rich beetroot juice (BR; providing 8.4 mmol NO3-∙day-1) and placebo (PLA). Compared to PLA, plasma nitrite concentration increased 178% with BR (P<0.01). There were no significant differences in muscle oxyhemoglobin concentration ([O2Hb]), phase II VO2 kinetics or Tlim between BR and PLA when cycling at 35 rpm (P>0.05). However, when cycling at 115 rpm, muscle [O2Hb] was higher at baseline and throughout exercise, phase II VO2 kinetics was faster (47 ± 16 s vs. 61 ± 25 s; P<0.05) and Tlim was greater (362 ± 137 s vs. 297 ± 79 s; P<0.05) with BR compared to PLA. These results suggest that short-term BR supplementation can increase muscle oxygenation, expedite the adjustment of oxidative metabolism and enhance exercise tolerance when cycling at a high, but not a low, pedal cadence in healthy recreationally-active subjects. These findings support recent observations that NO3- supplementation may be particularly effective at improving physiological and functional responses in type II muscle fibers.
Copyright © 2014, Journal of Applied Physiology