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Agreement between muscle oxygen saturation from two commercially available systems in endurance running: Moxy Monitor versus Humon Hex

Analysis of changes in muscle oxygen saturation (SmO2) in sport settings has become common due to its precise, continuous and non-invasive ability to provide measurements of a particular muscle using near-infrared spectroscopy (NIRS). Therefore, this study aims to determine level of agreement between two affordable NIRS-based oximeter wearable systems for measuring SmO2 level in the vastus lateralis in endurance runners. Seventeen trained endurance male runners (age: 34.2 ± 8.1 years; body mass: 70.5 ± 6.1 kg; height: 1.75 ± 0.04 m; BMI: 23 ± 1.7) completed a submaximal 60-min run-to-exhaustion treadmill running protocol trying to cover the longest possible distance. The SmO2 rates of the vastus lateralis were co-registered and continually obtained from two separate NIRS-based oximeter wearable systems over the running trial. The between-system means comparison reveals no significant differences in SmO2 at any point of the running protocol (p > 0.217) with trivial-to-small ES (ES < 0.27). Significant relationships (p < 0.05) were identified between systems with large and very large Pearson coefficients (r > 0.624). Additionally, substantial and almost perfect ICCs were obtained (ICC > 0.729). Bland-Altman plots exposed homoscedasticity (r2 < 0.1) for all the periods analysed during the running protocol, with mean differences lower than 3.2% over the time trial. The results found here show the level of agreement between two economical NIRS-based oximeter wearable systems. Notwithstanding their level of agreement, their interchangeable use is not recommended due to the variation shown for SmO2 levels.