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The pattern of arterial lactate concentration (La-) increase during incremental exercise was studied using a transformation defined by plotting log(La-) vs. log(VO2), where VO2 is O2 uptake. A plot of this function exhibits a phase of very slow increase followed by a phase of rapid increase, defining a transition in the underlying relationship between La- and VO2. These phases were found to be linear on the log-log plot; linear regression analysis may therefore be used to locate the transition between them (lactate threshold). A transition point was found at a lower VO2 on the semilog plot of log(La-) vs. VO2. Consideration of the data from all studies led to the conclusion that a more accurate result is provided by the log-log transformation. This analysis shows lactate to have a small, but significant, increase before the transition and to increase beyond it with a power law having an exponent of about 2.9. This result shows that, during incrementally increasing work rate tests, arterial lactate exhibits a threshold behavior, i.e., an abrupt transition from a phase of slow increase to a phase of rapidly accelerating increase.
Beaver et al. (Sun,) studied this question.