Cerebral and Muscle Oxygenation During Incremental Exercise in Normoxia and Hypoxia

Abstract

PURPOSE: To determine if fatigue at maximal aerobic power output was associated with a critical level of cerebral oxygenation, thirteen male cyclists performed incremental exercise tests (25 W·min−1 ramp) under normoxic (NORM: 21% FIO2) and acute hypoxic (HYPOX: 12% FIO2) conditions. METHODS: Near infrared spectroscopy (NIRS) was used to assess changes in cerebral and muscle oxygenation during incremental exercise. Concentration (μM) changes in oxy- and deoxy-hemoglobin (ΔO2Hb, Δ HHb) in the left vastus lateralis and frontal cortex (Oxymon, Artinis, The Netherlands) were measured and used to calculate an index of change in tissue oxygenation (ΔHbdiff = ΔO2Hb - ΔHHb). Repeated measures ANOVA analyses were performed across treatments and relative workrates (α = 0.05). RESULTS: During NORM, cerebral oxygenation (ΔHbdiff) was maintained up to 75% peak power output (Powerpeak), but decreased thereafter. Muscle oxygenation (ΔHbdiff) progressively decreased up to 75% Powerpeak, but was unchanged thereafter. During HYPOX cerebral oxygenation progressively decreased across all workrates, while muscle oxygenation again decreased up to 75% Powerpeak and remained unchanged thereafter. The magnitudes of changes were greater in HYPOX than NORM for cerebral but not muscle ΔHbdiff at 100% Powerpeak. CONCLUSION: These results demonstrate a large tolerance for changes in cerebral oxygenation at maximal aerobic power output and do not support the notion that a critical level of frontal cortex oxygenation limits exercise in NORM.Figure