Ventilatory and plasma lactate response with different exercise protocols: a comparison of methods.

The purpose of this study was to compare the methods used to identify abrupt changes in ventilation or plasma lactate (LA) during exercise. Ten males randomly performed a 1-, 3-, and 5-min, 30-W incremental cycle ergometer test to fatigue. The first change in VE and VCO2 relative to VO2 (ventilation threshold, VT1) was determined from plots of VE, VE X VO2-1, and excess CO2 vs VO2. Data were also analyzed for a second change in VE (VT2) relative to both VCO2 and VO2 using plots of VE and VE X VCO2(-1) vs VO2 and semi-log plots of VE X VO2(-1) and VE X VCO2(-1) vs VO2. Arterialized blood samples were taken each 1.0, 1.5, or 2.5 min for the 1-, 3-, and 5-min tests, respectively, to determine the LA threshold (LT) and the onset of blood lactate accumulation (4 mM, OBLA) and 1, 2, 5, 7.5, and 10 min after all tests to calculate the individual anaerobic threshold (IAT). At weekly intervals, subjects also exercised for 10 min at eight different power outputs (W) to define the onset of plasma lactate accumulation (OPLA). Results showed that VO2max was significantly higher for the 1-min (3.88 l X min-1)vs the 3- or 5-min tests (3.65 l X min-1). With increasing W duration, VT1 from either VE or VE X VO2-1 vs VO2 were similar (1.77 vs 1.72 l X min-1) but significantly lower using excess CO2 (1.23 l X min-1) . VO2 at LT (1.62 l X min-1) and OPLA (1.73 l X min-1) were similar to VT1.(ABSTRACT TRUNCATED AT 250 WORDS)