The anaerobic threshold measurement in exercise testing.

The exercise intensity (VO2) above which aerobic energy production starts to be supplemented by anaerobic mechanisms is termed the anaerobic threshold (AT). Lactic acid is produced at an increased rate above this work level. Since this acid is almost completely buffered by HCO-3, the rate of CO2 production increases in excess of that being derived from oxidative metabolism. Thus measurement of this excess CO2, or some reflection of it, can be used during exercise to measure the AT noninvasively. The AT has great physiologic significance, as it demarcates the work rate that the subject can perform for a prolonged period and above which a metabolic acid occurs.