Abstract des Autors

During exercise, the level of VO2 above which aerobic energy production is supplemented by anaerobic mechanisms, causing a sustained increase in lactate, is termed the anaerobic threshold (AT). The increase in lactate during muscular exercise is typically caused by an inadequate O2 supply to the mitochondria. Altering the O2 transport to muscles will affect the AT. The conversion of pyruvate to lactate enables the anaerobic generation of high energy phosphate needed to perform heavy exercise. Lactic acidosis develops at a metabolic rate that is specific to the individual and the task being performed. The AT can be measured directly from lactate concentration. It can also be measured from HCO3- decrease since HCO3- is the primary buffer for lactic acid and changes reciprocally with lactate. But most conveniently, changes in gas exchange caused by the physical-chemical event of buffering of lactic acid by HCO3- can be used to detect the AT during exercise. To estimate the AT by gas exchange methods, VCO2 is plotted as a continuous function of VO2 (V-slope analysis) as exercise work rate is increased. The break-point in this plot reflects the obligate buffering of increasing lactic acid production by HCO3-. The AT measured by the V-slope analysis appears to be a sensitive index of the development of metabolic acidosis even in subjects with irregular breathing, reduced chemoreceptor sensitivity, or impaired respiratory mechanics. The AT is an important functional demarcation since the physiologic responses to exercise are more demanding and different above the AT compared to below the AT. Above the AT, in addition to the development of metabolic acidosis, exercise endurance is reduced, glycogen utilization is accelerated, VO2 kinetics are slowed so that a steady state is delayed or not achieved, VCO2 is increased relative to VO2 and ventilation increases disproportionately to VO2. In addition, above the AT, the lowest capillary PO2 is reached and increased blood O2 extraction by muscle occurs due to the dissociation of oxyhemoglobin by H+ produced with lactate. Thus, the AT is an important assessment of the ability of the cardiorespiratory system to supply O2 during exercise at a rate adequate to prevent muscular anaerobiosis, and its associated functional changes. Verf.-Referat