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

Use of muscle oxygen saturation (SmO₂) 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 SmO₂ to identify training zones. The objective of this study was to evaluate the metabolic zones by SmO₂: 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 (VO₂), energy expenditure (kcal/min) and SmO₂ were measured. Data were analysed using the ANOVA test, ROC curves and multiple linear regressions. Significance was established at p ≤ 0.05. SmO₂ 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, SmO₂ together with weight, HR and output power have the ability to predict VO₂ and energy expenditure by 89% and 90%, respectively. We conclude that VO₂ and energy expenditure values can be approximated using SmO₂ together with other physiological parameters and SmO₂ measurements can be a complementary parameter to discriminate aerobic workload and anaerobic workload in athletes.