O2 Uptake Kinetics During Knee Extension And Leg Cycling Exercise In The Moderate-intensity Domain

Abstract

During the transition to the same relative intensity of exercise in the moderate-intensity domain the phase II time constant for O2 uptake (tVO2) and the VO2 gain (DVO2/DWR) tend to be greater with knee-extension (KE) than with leg cycling exercise (CE), however, the response at the same absolute work rate (WR) has not been established. PURPOSE: To examine the adaptation of pulmonary VO2 during the transition to the same relative and same absolute WRs in the moderate-intensity domain. METHODS: Four younger subjects completed an incremental exercise test to volitional fatigue during both alternate-leg KE and CE to estimate lactate threshold (θL) and peak VO2. Subjects then completed four step transitions in WR from light- to a moderate-intensity exercise corresponding to 90% θL (KErel, CErel), as well as four step transitions during CE from light-intensity to an absolute WR equal to that used during KErel (CEabs). A cadence of 50 rpm was maintained throughout all testing with KE and CE. VO2 was measured breath-by-breath using a volume turbine and mass spectrometer. The phase II VO2 response was modeled using a monoexponential function and non-linear regression techniques. RESULTS: The tVO2 was greater (p<0.05) in KErel (28 (7) s; mean (± SD)) than in CErel (15 (2) s) and in CEabs (16 (4) s) The VO2 gain was greater (p<0.05) in KErel (15.3 (2.?) ml · min-1 · W-1) than in CErel (8.5 (3.1) ml · min-1 · W-1), but not different from that found in CEabs (11.5 (6.6) ml · min-1 · W-1). CONCLUSION: The tendency for a greater tVO2 and VO2 gain during the transition to the same relative and same absolute intensity of exercise using KE compared to CE may be related to biomechanical differences or to the different muscle fibres or muscle groups recruited during the exercise transition within each modality. Supported by NSERC