Bicarbonate buffering of lactic acid generated during exercise

The pattern of decrease in arterial bicarbonate concentration (HCO3-]) during progressive incremental exercise was compared with that of the rise in arterial lactate (La-]) to determine the degree of buffering of lactic acid by bicarbonate. A mathematical model was derived for the change in HCO3-] beyond the lactate threshold. This was based on a log-log transformation of the data, a model previously found to provide a very good fit to the La-]-O2 consumption (VO2) relationship. The results of the analysis of incremental exercise data from 10 subjects show that the decrease in HCO3-] very nearly matches the increase in La-]. However, it was found by comparing regression models that the correspondence between HCO3-] and La-] could be improved by assuming that the HCO3-] decrease was delayed until the arterial lactate level had increased by approximately 0.4 meq/l. This result is compatible with the existence of buffering mechanisms in the cell which buffer the initial increase of lactic acid. Beyond this initial buffering, lactic acid appears to be buffered almost entirely by the bicarbonate buffer system.