Relationship Between Muscle Oxygenation and Oxygen Uptake During Exercise in the Heat: 94 May 29 9:30 AM - 9:45 AM

Exercising in the warm environments increases thermoregulatory demand for skin blood flow, influencing oxygen delivery and oxygen consumption (VO2) systemically and to active muscle. Near infrared spectroscopy (NIRS) is a non-invasive technique that indirectly assesses local tissue oxygen delivery and VO2 and accounts for systemic oxygen uptake. Limited evidence exists on the relationship between muscle oxygenation and systemic oxygen uptake during combined heat stress and exercise. PURPOSE: To examine the relationship between muscle oxygenation and VO2 at different exercise intensities in the heat. METHODS: Six participants (4 males, 2 females, age:21±1.0 years, height: 173.41± 15.84 cm, weight: 73.14±17.28 kg, VO2max: 46.41±3.53 ml·kg-1·min-1) performed a treadmill exercise protocol (30°C, 60% relative humidity) with 10 minutes each at 30%, 40%, 60%, 70%, and 80% of velocity at VO2max. NIRS (Moxy, Fortiori Design LLC, Minnesota, USA) was used to assess muscle oxygen saturation (SmO2) of the vastus lateralis muscle and systemic VO2 was measured using expiratory gas analysis. Pearson correlations coefficients were calculated to evaluate the relationship between average SmO2, relative changes from baseline (Δ) in SmO2, mean VO2 at percent of peak velocity, and percent of VO2max. RESULTS: There was a positive correlation between ΔSmO2 and VO2 at 80% of peak velocity (r=0.857, p=0.029). There were no significant correlations between ΔSmO2 and VO2 at 30%, 40%, 60%, or 70% of peak velocity (30%: r=0.483, p=0.332;40%: r=0.554, p=0.254; 60%: r=0.653, p=0.160; 70%: r=0.620, p=0.189). There were no significant correlations between mean SmO2, VO2 at percent of peak velocity, or percent VO2max. CONCLUSION: At 80% of peak velocity, ΔSmO2 and VO2 are positively correlated and may suggest this relationship exists while running at high intensities. Therefore, the relationship between NIRS measured SmO2 and oxygen uptake during exercise in the heat must be further explored in order to use NIRS as an assessment for energy efficiency and substrate utilization.