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Training zones through muscle oxygen saturation during a graded exercise test in cyclists and triathletes

: Use of muscle oxygen saturation (SmO 2 ) has been validated as a performance factor during incremental exercise with portable near-infrared stereoscopy (NIRS) technology. However, there is little knowledge about the use of SmO 2 to identify training zones. The objective of this study was to evaluate the metabolic zones by SmO 2 : maximum lipid oxidation zone (Fatmax), ventilatory thresholds (VT1 and VT2) and maximum aerobic power (MAP) during a graded exercise test (GXT). Forty trained cyclists and triathletes performed a GXT. Output power (W), heart rate (HR), oxygen consumption (VO 2 ), energy expenditure (kcal/min) and SmO 2 were measured. Data were analysed using the ANOVA test, ROC curves and multiple linear regressions. Significance was established at p ≤ 0.05. SmO 2 decreases were observed from baseline (LB) to Fatmax ( Δ = -16% p < 0.05), Fatmax to VT1 ( Δ = -16% p < 0.05) and VT1 to VT2 ( Δ = -45% p < 0.01). Furthermore, SmO 2 together with weight, HR and output power have the ability to predict VO 2 and energy expenditure by 89% and 90%, respectively. We conclude that VO 2 and energy expenditure values can be approximated using SmO 2 together with other physiological parameters and SmO 2 measurements can be a complementary parameter to discriminate aerobic workload and anaerobic workload in athletes.