Influence of Running Velocity and Hypoxic Exposure on Vastus Lateralis Muscle Oxygenation

Purpose: We investigated the effects of manipulating running velocity and hypoxic exposure on vastus lateralis muscle oxygenation levels during treadmill running. Methods: Eleven trained male distance runners performed 7 randomized runs at different velocities (8, 10, 12, 14, 16, 18, and 20 km<middle dot>h(-1)), each lasting 45 seconds on an instrumented treadmill in normoxia (fraction of inspired oxygen [FiO(2)] = 20.9%), moderate hypoxia (FiO(2) = 16.1%), high hypoxia (FiO(2) = 14.1%), and severe hypoxia (FiO(2) =13.0%). Continuous assessment of Tissue Saturation Index (TSI) in the vastus lateralis muscle was conducted using near-infrared spectroscopy. Subsequently, changes in TSI (Delta TSI) data over the final 20 seconds of each run were compared between velocities and conditions. Results: There was a significant velocity x condition interaction for Delta TSI% (P < .001, eta(2)(p) = .19), with a smaller Delta TSI% decline in normoxia compared with high hypoxia and severe hypoxia at 8 km<middle dot>h(-1) (g = 1.30 and 1.91, respectively), 10 km<middle dot>h(-1) (g = 0.75 and 1.43, respectively), and 12 km<middle dot>h(-1) (g = 1.47 and 1.95, respectively) (pooled values for all conditions: P < .037). The Delta TSI% decline increased with each subsequent velocity increment from 8 km<middle dot>h(-1) (-9.2% [3.7%]) to 20 km<middle dot>h(-1) (-22.5% [4.1%]) irrespective of hypoxia severity (pooled values for all conditions: P < .048). Conclusions: Running at slower velocities in conjunction with high and severe hypoxia reduces vastus lateralis muscle oxygenation levels. Muscle Delta TSI% proves to be a sensitive indicator, underscoring the potential use of near-infrared spectroscopy as a reference index of internal load during treadmill runs.