Oxygen uptake kinetics and lactate concentration during exercise in humans

Area of Science:

• Exercise Physiology
• Human Physiology
• Sports Science

Background:

• Oxygen uptake (VO2) kinetics typically reach steady state within 3 minutes during moderate-intensity exercise.
• Above the lactate threshold (LT), VO2 kinetics exhibit a slow phase, delaying or preventing steady state.
• Understanding this slow phase is crucial for interpreting exercise responses at higher intensities.

Purpose of the Study:

• To correlate the characteristics of the slow phase of VO2 kinetics with blood lactate increases during constant-load exercise.
• To investigate the relationship between VO2 kinetics and blood lactate accumulation above the LT.

Main Methods:

• Six healthy males completed 6 randomized, constant-load cycle exercise tests.
• Exercise tests were performed below and at various levels above the gas exchange-determined LT.
• Measurements included oxygen uptake (VO2) and blood lactate concentrations.

Main Results:

• The slow kinetic phase of VO2 (delta VO2 (6-3) and delta VO2(term-3)) was linearly correlated with the increase in blood lactate.
• VO2 at exercise termination above LT exceeded predictions based on sub-LT VO2-work rate relationships.
• Work rates above LT led to rising lactate and VO2 curves until fatigue, unlike lower work rates where asymptotes were reached.

Conclusions:

• Positive delta VO2 (6-3) and delta VO2(term-3) values during constant-load exercise are indicative of work rates above the LT.
• The magnitude of the slow VO2 phase is strongly correlated with the increase in blood lactate.
• These findings highlight the link between VO2 kinetics and metabolic stress above the lactate threshold.