Transcutaneous pCO2-monitoring for the evaluation of the anaerobic threshold. Comparison to lactate and ventilatory thresholds.

The monitoring of transcutaneous pCO2 (pCO2(tc) is an alternative to the invasive determination of the anaerobic threshold by analysis of arterial lactate concentration or to the uncomfortable determination of the ventilatory threshold. We compared the threshold determination by pCO2(tc)-monitoring to the 4 mmol/l lactate threshold and to the ventilatory threshold (point where the ventilatory equivalent of oxygen started to increase continuously) in 15 athletes during cycle exercise. The first distinct deflection point in the pCO2(tc) time course after the start of exercise was chosen to indicate the anaerobic threshold. The mean threshold determined by pCO2(tc) occurred at the same workload as the ventilatory threshold but at a lower workload than the lactate threshold. In spite of the good correspondence in the respective means there was a wide range of individual differences between the pCO2(tc) derived thresholds and both reference thresholds. Thus, looking at an individual, the continuous monitoring of the pCO2(tc) does not provide reliable data on the occurrence of the transition from aerobic to anaerobic metabolism.