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

Area of Science:

• Exercise Physiology
• Human Performance
• Cardiorespiratory Fitness

Background:

• During constant-load exercise above the lactate threshold (Tlac), oxygen consumption (VO2) may not reach a steady state.
• A delayed, elevated VO2 (VO2 slow component) can occur, increasing the oxygen cost of exercise.
• This phenomenon has been observed at discrete intensities, but its onset during incremental exercise is less understood.

Purpose of the Study:

• To investigate the relationship between pulmonary VO2 and running speed across various exercise intensities.
• To determine if the onset of the VO2 slow component aligns with the lactate threshold (Tlac) during incremental treadmill exercise.
• To test the hypothesis that a sufficiently long stage duration in incremental tests would reveal the VO2 slow component coinciding with Tlac.

Main Methods:

• Five male subjects completed four identical 7-minute stage treadmill tests.
• Running speed increased by 0.5 km/h each stage.
• Lactate threshold (Tlac) was determined from fingertip capillary blood samples.
• Expired air was collected mid-stage to calculate the change in VO2 (deltaVO2) within each stage.

Main Results:

• A significant increase in deltaVO2 was observed at running speeds above the lactate threshold (Tlac).
• No significant increase in deltaVO2 was found at speeds below Tlac.
• This indicates a clear rise in the oxygen cost of exercise once Tlac is surpassed.

Conclusions:

• The VO2 slow component is closely associated with the onset of lactic acidosis.
• A non-linear relationship exists between VO2 and exercise intensity above Tlac during incremental treadmill running.
• This study confirms the link between metabolic changes and increased oxygen demand during intense exercise.