Statistical evidence consistent with two lactate turnpoints during ramp exercise

A number of studies have identified the existence of two ventilation thresholds during ramp or incremental exercise to exhaustion on the cycle ergometer. This study was undertaken to investigate whether two threshold turnpoints could be identified in blood lactate concentration data collected at such times. Five trained athletes provided serial blood samples on several occasions each during a 3-month period of training. Blood lactate concentration was analysed by fitting models with no, one or two turnpoints. Ordinary residuals from the first two models were often found to exhibit an oscillatory behaviour consistent with the existence of two turnpoints in lactate concentration. A comparative analysis of goodness of fit of these models revealed that the model with two turnpoints was significantly better than either of the simpler models. This suggests that two transitions exist, which divide the time domain for blood lactate concentration in ramp exercise into three regions. These two transitions may correspond to the two ventilation thresholds.