Lactate accumulation relative to the anaerobic and respiratory compensation thresholds

Anaerobic thresholds of five male subjects were determined invasively (ATi), from a marked increase in plasma lactate above resting levels (delta La), and noninvasively (ATn), from a nonlinear increase in minute ventilation (VE) during incremental work (IW) leg cycling tests; work rate was increased 30 W every 2 min. Each subject also performed four constant-load work (CLW) tasks just above and just below their ATn and respiratory compensation threshold (RCT), i.e., the point expressed as O2 consumption (VO2) or work rate, at which VE increases disproportionally to CO2 output during IW. In four of the five subjects the ATn preceded the ATi during IW. Yet the ATn delineated the CLW in which marked lactate accumulation did or did not occur. During CLW just above the ATn in these same four subjects, VE/VO2 and fractional expired O2 (FEO2) peaked well before delta La plateaued. These findings suggest that exercise hyperventilation is not necessarily proportional to increases in plasma lactate.