Detection of lactate threshold by including haemodynamic and oxygen extraction data.

To date, few attempts have been made to correlate cardiovascular variables to lactate threshold (L(T)). This study was designed to determine the relationship between the accumulation of blood lactate and several haemodynamic variables during exercise. Eight male volunteer cyclists performed an incremental test on an electromagnetically braked cycle-ergometer consisting of a 50 W linear increase in workload every 3 min up to exhaustion. Blood lactate was measured with a portable analyser during each exercise step. Oxygen consumption (VO(2)) and pulmonary ventilation were measured by means of a mass spectrometer while heart rate, stroke volume and cardiac output (CO) were assessed by impedance cardiography. The arterio-venous oxygen difference (A-V O(2) Diff) was obtained by dividing VO(2) by CO. By applying the D(max) mathematical method, L(T) and thresholds of ventilatory and haemodynamic parameters were calculated. The Bland and Altman statistics used to assess agreement between two methods of measurement were applied in order to evaluate the agreement between L(T) and thresholds derived from ventilatory and haemodynamic data. The main result was that most of the haemodynamic variables did not provide thresholds which could be used interchangeably with L(T). Only the threshold of A-V O(2) Diff showed mean values that were no different compared to L(T) together with limits of agreement that were not very wide between thresholds (below +/-25%). Hence of the haemodynamic parameters, A-V O(2) Diff appears to be the one most closely coupled with lactate accumulation and consequently it is also the most suitable for non-invasive calculation of the L(T).