The anaerobic threshold as determined before and during lactic acidosis

Summary

During this study the relationships between venous lactate concentration and associated changes in respiratory gas exchange were investigated. Five men performed two successive incremental exercise tests to exhaustion on an electronically braked cycle ergometer. These tests were separated by a 5 min rest period. During the initial test venous lactate concentrations showed a characteristic curvilinear increase and the anaerobic threshold (AT1) was determined conventionally. During the second test lactate concentrations were still decreasing at higher work rates than the AT1, and a second anaerobic threshold (AT2) was determined as the point where lactate concentrations again increased. The departure from linearity of the ventilatory response to both exercise tests occurred at a similar work rate, irrespective of whether venous lactate concentrations were increasing or decreasing. Carbon dioxide production was similar during the two exercise tests. The anaerobic thresholds as determined by respiratory gas analysis (ATR) were therefore similar for both tests. Results of this study indicate that changing venous lactate concentrations were not responsible for the ventilatory drive which occurred at the ATR. The venous lactate response to work at a constant rate determined within the range AT1–AT2 was also investigated. It was concluded that the lactate response to constant work rate will vary predictably at work rates falling within the AT1 to AT2 range. At AT1 no increase in venous lactate concentrations occurred, while at AT2 these increased progressively, and the test was terminated at varying times (12–15 min) due to subject exhaustion. At work rates determined from the ATR venous lactate concentrations varied according to the placement of the ATR within the AT1 AT2 range.