A disproportionate increase in VO2 coincident with lactate threshold during treadmill exercise

Purpose:The purpose of this study was to assess the relationship between pulmonary (V) over dot O-2 and running speed over a range of exercise intensities. During constant-load cycle exercise above the lactate threshold (T-lac), it has been shown that (V) over dot O-2 does not attain a steady state within 3 min but continues to rise until either a delayed but elevated steady-state (V) over dot O-2 is attained or exhaustion occurs. Since this greater oxygen cost of exercise ((V) over dot O-2, slow component) has only been demonstrated at discrete exercise intensities above T-lac it was hypothesised that the onset of the 90, slow component would coincide with T-lac during an incremental test if the stage durations were of sufficient length. Methods: Five male subjects (mean +/- SD age 31 +/- 2 yr; (V) over dot O-2peak 60.1 +/- 5.8 mL.kg(-1).min(-1)) performed four identical treadmill tests within an 8-d period. The tests involved the completion of six stages of 7-min duration. Running speed was increased by 0.5 km.h(-1) between stages. In the first test, fingertip capillary blood was sampled at the end of each stage for determination of T-lac. For all tests expired air was collected into Douglas bags from 3.0 to 3.75 min and from 6.0 to 6.75 min of each stage to determine any increase in (V) over dot O-2 (Delta(V) over dot O-2) over the duration of the stage. Results: The mean Delta(V) over dot O-2 for each stage over the four tests was determined for each subject. Repeated measures ANOVA with post-hoc Tukey rests revealed a significant increase in Delta(V) over dot O-2 at running speeds above, but nor below, T-lac. Conclusions: The results of this study confirm the close association between the (V) over dot O-2 slow component and the onset of lactic acidosis and demonstrate alinearity in the (V) over dot O-2-exercise intensity relationship above T-lac for incremental treadmill exercise.