Abstract
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 V̇E and V̇CO2 relative to V̇O2 (ventilation threshold, VTI) was determined from plots of V̇E, V̇E·V̇O2
-1, and excess CO2 vs V̇O2. Data were also analyzed for a second change in V̇E (VT2) relative to both V̇CO2 and V̇O2 using plots of V̇E, and V̇E·V̇O2
-1, vs V̇O2 and semilog plots of V̇E·V̇O2
-1 and V̇E·V̇O2
-1, vs V̇O2. 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 V̇O2max was significantly higher for the 1-min (3.88 l·min-1)vs the 3- or 5-min tests (3.65 I·min-1). With increasing W duration, VT1 from either V̇E or V̇E·V̇O2
-1 vs V̇O2 were similar (1.77 vs 1.72 l·min-1) but significantly lower using excess CO2 (1.23 l·min-1). V̇O2 at LT (1.62 l·min-1) and OPLA (1.73 l·min-1) were similar to VT1. W duration had no influence on VT2 determined from either V̇E or 1n V̇E·V̇CO2
-1 vs V̇O2 (2.93 l·min-1). V̇O2 at OBLA (2.85 l·min-1) did not differ from VT2. V̇O2 at IAT was significantly less than VT2 and OBLA and was influenced by W duration. It was concluded that both VT1 and VT2 were not influenced by the duration of the step increment whereas the determination of IAT may be misinterpreted with a fast incremental test. In addition, the use of excess CO2 does not produce a valid estimate of VT1.
Key words
ventilation threshold - lactate threshold - individual anaerobic threshold - onset of plasma and blood lactate accumulation
