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

Purpose:The purpose of this study was to assess the relationship between pu lmonary (V) over dot O-2 and running speed over a range of exercise intensi ties. During constant-load cycle exercise above the lactate threshold (T-la c), 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 stea dy-state (V) over dot O-2 is attained or exhaustion occurs. Since this grea ter oxygen cost of exercise ((V) over dot O-2, slow component) has only bee n demonstrated at discrete exercise intensities above T-lac it was hypothes ised that the onset of the 90, slow component would coincide with T-lac dur ing an incremental test if the stage durations were of sufficient length. M ethods: Five male subjects (mean +/- SD age 31 +/- 2 yr; (V) over dot O-2pe ak 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 sta ge to determine any increase in (V) over dot O-2 (Delta(V) over dot O-2) ov er the duration of the stage. Results: The mean Delta(V) over dot O-2 for e ach stage over the four tests was determined for each subject. Repeated mea sures ANOVA with post-hoc Tukey rests revealed a significant increase in De lta(V) over dot O-2 at running speeds above, but nor below, T-lac. Conclusi ons: 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 demonstr ate alinearity in the (V) over dot O-2-exercise intensity relationship abov e T-lac for incremental treadmill exercise.