The Reliability Of Using NIRS To Determine The Power Associated With Maximal Metabolic Steady State

PURPOSE: Investigate the reliability of using muscle oxygen saturation (%SmO2) measured with near-infrared spectroscopy to determine the power associated with the maximal metabolic steady state. METHODS: Twenty-five endurance-trained participants (12 women, Age: 29 ± 7 years, V̇O2MAX: 53.2 ± 6.9 ml·kg-1·min-1, Peak Power: 342 ± 64 W) completed six visits. Maximal oxygen uptake and gas exchange parameters were determined via a graded exercise test on a cycle ergometer. Participants then completed four weekly cycling protocols consisting of four, 4-minute stages spanning from moderate to severe exercise intensity domains. Menstrual cycle phase did not dictate visit order for women participants. During each stage, %SmO2 was measured using near-infrared spectroscopy on the rectus femoris. The %SmO2 zero-slope, which corresponds to a balanced oxygen supply with utilization, determined the power associated with the maximal metabolic steady state (MMSS) for each visit. Specifically, a linear regression between stage power (x-axis) and the slope of the %SmO2 response during each stage (y-axis) was used to calculate the power at a slope of zero. Differences in power at MMSS across visits were examined via one-way ANOVA, and reliability was assessed using the intraclass correlation coefficient (ICC 2,1 - two-way random effects, single rater, absolute agreement) as well as the standard error of measurement (SEM) and coefficient of variation (CV). RESULTS: The main effect of visit was not significant for power at MMSS (p = 0.111). The ICC across visits was 0.953 (95%CI: 0.917-0.978) indicating excellent reliability with a SEM of 9.2 W and CV of 4.2%. CONCLUSIONS: These results demonstrate the %SmO2 zero-slope method can reliability estimate the power at MMSS using NIRS Supported by: Wu Tsai Human Performance Alliance at the University of Oregon