A disproportionate increase in O2 coincident with lactate threshold during treadmill exercise

Jones, Andrew M., Carter, Helen and Doust, Jonathan H. (1999) A disproportionate increase in O2 coincident with lactate threshold during treadmill exercise. Medicine and science in sports and exercise, 31 (9). pp. 1299-1306. ISSN 0195-9131

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Abstract

Purpose: The purpose of this study was to assess the relationship between pulmonary O2 and running speed over a range of exercise intensities. During constant-load cycle exercise above the lactate threshold (Tlac), it has been shown that O2 does not attain a steady state within 3 min but continues to rise until either a delayed but elevated steady-state O2 is attained or exhaustion occurs. Since this greater oxygen cost of exercise ( O2 slow component) has only been demonstrated at discrete exercise intensities above Tlac, it was hypothesised that the onset of the O2 slow component would coincide with Tlac during an incremental test if the stage durations were of sufficient length. Methods: Five male subjects (mean +/- SD age 31 +/- 2 yr; O2peak 60.1 +/- 5.8 mL[middle dot]kg-1[middle dot]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[middle dot]h-1 between stages. In the first test, fingertip capillary blood was sampled at the end of each stage for determination of Tlac. 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 O2 (ΔO2) over the duration of the stage. Results: The mean Δ O2 for each stage over the four tests was determined for each subject. Repeated measures ANOVA with post-hoc Tukey tests revealed a significant increase in Δ O2 at running speeds above, but not below, Tlac. Conclusions: The results of this study confirm the close association between the O2 slow component and the onset of lactic acidosis and demonstrate alinearity in the O2-exercise intensity relationship above Tlac for incremental treadmill exercise.