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

Abstract

We investigated the effects of manipulating running velocity and hypoxic exposure on vastus lateralis muscle oxygenation levels during treadmill running. Eleven trained male distance runners performed 7 randomized runs at different velocities (8, 10, 12, 14, 16, 18, and 20km·h-1), each lasting 45seconds on an instrumented treadmill in normoxia (fraction ofinspired oxygen[FiO2] = 20.9%), moderate hypoxia (FiO2 = 16.1%), high hypoxia (FiO2 = 14.1%), and severe hypoxia (FiO2 = 13.0%). Continuous assessment of Tissue Saturation Index (TSI) in the vastus lateralis muscle was conducted using near-infrared spectroscopy. Subsequently, changes in TSI (ΔTSI) data over the final 20seconds of each run were compared between velocities and conditions. There was a significant velocity × condition interaction for ΔTSI% (P < .001, ηp2=.19), with a smaller ΔTSI% decline in normoxia compared with high hypoxia and severe hypoxia at 8km·h-1 (g = 1.30 and 1.91, respectively), 10km·h-1 (g = 0.75 and 1.43, respectively), and 12km·h-1 (g = 1.47 and 1.95, respectively) (pooled values for all conditions: P < .037). The ΔTSI% decline increased with each subsequent velocity increment from 8km·h-1 (-9.2% [3.7%]) to 20km·h-1 (-22.5% [4.1%]) irrespective of hypoxia severity (pooled values for all conditions: P < .048). Running at slower velocities in conjunction with high and severe hypoxia reduces vastus lateralis muscle oxygenation levels. Muscle ΔTSI% proves to be a sensitive indicator, underscoring the potential use of near-infrared spectroscopy as a reference index of internal load during treadmill runs.