Muscle oxygen saturation rates coincide with lactate-based exercise thresholds

Abstract

Introduction: Monitoring muscle metabolic activity via blood lactate is a useful tool for understanding the physiological response to a given exercise intensity. Recent indications suggest that skeletal muscle oxygen saturation (SmO₂), an index of the balance between local O₂ supply and demand, may describe and predict endurance performance outcomes.

Purpose: We tested the hypothesis that SmO₂ rate is tightly related to blood lactate concentration across exercise intensities, and that deflections in SmO₂ rate would coincide with established blood lactate thresholds (i.e., lactate thresholds 1 and 2).

Methods: Ten elite male soccer players completed an incremental running protocol to exhaustion using 3-min work to 30 s rest intervals. Blood lactate samples were collected during rest and SmO₂ was collected continuously via near-infrared spectroscopy from the right and left vastus lateralis, left biceps femoris and the left gastrocnemius.

Results: Muscle O₂ saturation rate (%/min) was quantified after the initial 60 s of each 3-min segment. The SmO₂ rate was significantly correlated with blood lactate concentrations for all muscle sites; RVL, r = - 0.974; LVL, r = - 0.969; LG, r = - 0.942; LHAM, r = - 0.907. Breakpoints in SmO₂ rate were not significantly different from LT1 or LT2 at any muscle sites (P > 0.05). Bland-Altman analysis showed speed threshold estimates via SmO₂ rate and lactate are similar at LT2, but slightly greater for SmO₂ rate at LT1.

Conclusions: Muscle O₂ saturation rate appears to provide actionable information about maximal metabolic steady state and is consistent with bioenergetic reliance on oxygen and its involvement in the attainment of metabolic steady state.

Keywords: Exercise capacity; Lactate; NIRS; SmO2.