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

Increased local blood supply is thought to be one of the mechanisms underlying oxidative adaptations to interval training regimes. The relationship of exercise intensity with local blood supply and oxygen availability has not been sufficiently evaluated yet. The aim of this study was to examine the effect of six different intensities (40-90% peak oxygen uptake, VO_2peak ) on relative changes in oxygenated, deoxygenated and total haemoglobin (ΔO₂ Hb, ΔHHb, ΔTHb) concentration after exercise as well as end-exercise ΔHHb/ΔVO₂ as a marker for microvascular O₂ distribution. Seventeen male subjects performed an experimental protocol consisting of 3 min cycling bouts at each exercise intensity in randomized order, separated by 5 min rests. ΔO₂ Hb and ΔHHb were monitored with near-infrared spectroscopy of the vastus lateralis muscle, and VO₂ was assessed. ΔHHb/ΔVO₂ increased significantly from 40% to 60% VO₂ peak and decreased from 60% to 90% VO₂ peak. Post-exercise ΔTHb and ΔO₂ Hb showed an overshoot in relation to pre-exercise values, which was equal after 40-60% VO_2peak and rose significantly thereafter. A plateau was reached following exercise at ≥80% VO_2peak . The results suggest that there is an increasing mismatch of local O₂ delivery and utilization during exercise up to 60% VO_2peak . This insufficient local O₂ distribution is progressively improved above that intensity. Further, exercise intensities of ≥80% VO_2peak induce highest local post-exercise O₂ availability. These effects are likely due to improved microvascular perfusion by enhanced vasodilation, which could be mediated by higher lactate production and the accompanying acidosis.