Sodium bicarbonate ingestion alters the slow but not the fast phase of VO2 kinetics.
OBJECTIVE
The influence of metabolic alkalosis (ALK) on pulmonary O2 uptake (pVO2) kinetics during high-intensity cycle exercise is controversial. The purpose of this study was to examine the influence of ALK induced by sodium bicarbonate (NaHCO3) ingestion on pVO2 kinetics, using a sufficient number of repeat-step transitions to provide high confidence in the results obtained.


METHODS
Seven healthy males completed step tests to a work rate requiring 80% pVO2max on six separate occasions: three times after ingestion of 0.3 g x kg(-1) body mass NaHCO3 in 1 L of fluid, and three times after ingestion of a placebo (CON). Blood samples were taken to assess changes in acid-base balance, and pVO2 was measured breath-by-breath.


RESULTS
NaHCO3 ingestion significantly increased blood pH and [bicarbonate] both before and during exercise relative to the control condition (P < 0.001). The time constant of the phase II pVO2 response was not different between conditions (CON: 29 +/- 6 vs ALK: 32 +/- 7 s; P = 0.21). However, the onset of the pVO2 slow component was delayed by NaHCO3 ingestion (CON: 120 +/- 19 vs ALK: 147 +/- 34 s; P < 0.01), resulting in a significantly reduced end-exercise pVO2 (CON: 2.88 +/- 0.19 vs ALK: 2.79 +/- 0.23 L x min(-1); P < 0.05).


CONCLUSIONS
Metabolic alkalosis has no effect on phase II pVO2 kinetics but alters the pVO2 slow-component response, possibly as a result of the effects of NaHCO3 ingestion on muscle pH.
Berger
Nicolas J A
NJ
Department of Exercise and Sport Science, Manchester Metropolitan University, Hassall Road, Alsager, UK.
McNaughton
Lars R
LR
Keatley
Simon
S
Wilkerson
Daryl P
DP
Jones
Andrew M
AM
D000137:Acid-Base Imbalance / Q000097:blood*; D000328:Adult; D005080:Exercise Test; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007700:Kinetics; D019344:Lactic Acid / Q000097:blood; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects* / Q000502:physiology; D017693:Sodium Bicarbonate / Q000494:pharmacology*
D019344:Lactic Acid; D017693:Sodium Bicarbonate