DETERMINATION OF THE ANAEROBIC THRESHOLD BY GAS-EXCHANGE - BIOCHEMICAL CONSIDERATIONS, METHODOLOGY AND PHYSIOLOGICAL-EFFECTS

This paper explains the physiological and biochemical basis of the ana erobic threshold (AT), achieved during physical exercise. The lactate concentration is approximately the same at rest in relatively fit adul ts, in normal sedentary subjects in adult patients with heart disease. But during exercise, the increase of lactate is inversely related to the physical fitness of the individual. During incremental work, the l actate concentration increases initially very little until a distinct metabolic rate (VO2 AT) is reached at which lactate starts to increase steeply (anaerobic threshold / AT; VO2 AT). Above the anaerobic thres hold, accelerated glycolysis increases muscle lactic acidosis. This ac idosis is buffered primarily by bicarbonate. The bicarbonate-derived C O2 causes an increased alveolar CO2 output relative to O-2 uptake. Oxy gen uptake is increased virtually linearly with work rate in healthy s ubjects with a slope of approximately 10 mi O-2/min/Watt. VCO2 starts to increase more steeply in the mid-workrate range after an initial li near behavior. This steepening is caused by an increased CO2 productio n from the HCO3-buffering of lactic acid for the range of work rates a bove the AT. Below the AT, the slope of increase in VCO2 is l or sligh tly less, averaging 0.95. Above the AT; it is greater than l. The subm aximal exercise protocol for the determination of AT includes a period of 2-3 min of unloaded cycling, a ramp program with x Watt increase/m inute and a recovery period of 2 min. X is the rate of work rate incre ase per min, so that the incremental period of the exercise test lasts 8-10 min, stressing the patient for only a short time. The anaerobic threshold can be determined during the ramp program using the followin g four parameters: 1) steeper increase of VCO2 as compared to VO2 (V-s lope-method); 2) respiratory exchange ratio = 0.95; 3) PETO(2) increas e; 4) VE/VO2 increase. The V-slope-method can be successfully applied, not only in healthy volunteers, but also in patients suffering from c ardiac and/or pulmonary (breathing abnormalities) diseases. The so far published data show that the anaerobic threshold in healthy people an d patients is a highly reproducible, accurately measurable, securely a chievable parameter for the non-invasive evaluation of the individual cardiopulmonary exercise capacity.