[Correlations of cardiorespiratory and metabolic reactions in humans with graded physical load]

Bicycle ergometry tests of graded workloads were performed by 9 healthy men, aged 25 to 40 years. During the tests cardiorespiratory parameters, lactate and pyruvate concentrations, as well as lactate dehydrogenase (LDH) and NADP-dependent isocitrate dehydrogenase (ICDH) activities were measured. It was shown that the threshold of anaerobic metabolism can be measured not only by traditional methods (with respect to variations in pulmonary ventilation and venous blood lactate) but also in terms of ICDH increase as a function of the workload. Mathematical processing of the resulting data did not reveal a correlation between the total oxygen debt and lactate in blood. In contrast, a close correlation between the debt and LDH activity at the end of the test was found. These observations have demonstrated that biochemical measurements should find a wider application in evaluations of energy costs of various workloads.