A method for estimating the anaerobic threshold. The minute ventilation and oxygen consumption of a subject is monitored during a progressive exercise test on a treadmill or bicycle ergometer. The running or cycling speed at which minute ventilation increases disproportionately compared with oxygen consumption is called the respiratory threshold, ventilatory breakpoint, or ventilatory threshold. This is sometimes taken as being equivalent to the lactate threshold and to indicate the point at which there is a substantial switch from aerobic metabolism to anaerobic metabolism (see anaerobic threshold). The basis of this assumption is that increases in blood lactate levels are associated with a lowering of blood pH (i.e. blood becomes more acidic), stimulating chemoreceptors, which effect an increase in pulmonary ventilation through the action of the respiratory centres. However, this assumption has been seriously questioned because factors other than pH can contribute to the non-linear increase in minute ventilation.
Subjects: Sports and Exercise Medicine.