End-exercise ΔHHb/ΔVO₂ and post-exercise local oxygen availability in relation to exercise intensity

Area of Science:

• Exercise Physiology
• Sports Science
• Muscle Metabolism

Background:

• Interval training is linked to oxidative adaptations, potentially via increased local blood supply.
• The precise relationship between exercise intensity, local blood flow, and oxygen availability requires further investigation.

Purpose of the Study:

• To investigate the impact of varying exercise intensities (40-90% VO2peak) on muscle oxygenation.
• To evaluate the ratio of deoxygenated hemoglobin to oxygen uptake (ΔHHb/ΔVO2) as an indicator of microvascular oxygen distribution.

Main Methods:

• Seventeen male subjects completed 3-minute cycling bouts at six randomized intensities (40-90% VO2peak) with 5-minute rests.
• Near-infrared spectroscopy monitored oxygenated (ΔO2Hb), deoxygenated (ΔHHb), and total hemoglobin (ΔTHb) in the vastus lateralis.
• Oxygen uptake (VO2) was measured concurrently.

Main Results:

• The ΔHHb/ΔVO2 ratio increased up to 60% VO2peak and decreased from 60% to 90% VO2peak, indicating a shift in oxygen distribution.
• Post-exercise ΔTHb and ΔO2Hb showed an overshoot, significantly increasing above 60% VO2peak and plateauing at intensities ≥80% VO2peak.
• Exercise intensities of ≥80% VO2peak resulted in the highest local post-exercise oxygen availability.

Conclusions:

• Exercise intensities up to 60% VO2peak reveal a growing mismatch between oxygen delivery and utilization in the muscle.
• Higher exercise intensities (above 60% VO2peak) progressively improve local oxygen distribution and post-exercise oxygen availability.
• Enhanced vasodilation, possibly driven by lactate production and acidosis, likely mediates improved microvascular perfusion at higher intensities.