Assessing the feasibility of near-infrared spectroscopy for evaluating physiological exercise thresholds

To examine the feasibility of using near-infrared spectroscopy (NIRS) for physiological threshold detection and whether NIRS-derived parameters differ between highly-trained and less-trained cyclists. Twenty-seven male cyclists were divided into: highly trained endurance cyclists (EA) and recreational cyclists (RA). Participants performed a step-incremental cycling test to exhaustion. Ventilatory thresholds (VT₁ and VT₂) were determined using gas-exchange variables. NIRS sensor was placed on the vastus lateralis muscle to identify breakpoints corresponding to ventilatory thresholds. No significant differences were observed between NIRS-derived thresholds, compared to VT₁ and VT₂ (F = 1.04-1.33, p = 0.26-0.36). Moderate to strong correlations were found between NIRS-derived thresholds and ventilatory thresholds (r = 0.65-0.9, p < 0.01). A moderate correlation was found between maximal oxygen uptake and minimal tissue saturation index (TSI) value during the test (r = - 0.411, p = 0.037). EA group showed tendency towards lower minimal TSI values compared to RA group (MD = 5.46% TSI, p = 0.081). NIRS is a feasible tool for non-invasive assessment of ventilatory thresholds during incremental exercise. TSI, in particular, showed lower variability compared to other NIRS-derived parameters, and may therefore be more suitable for practical applications in sport science. Highly trained athletes demonstrated distinct physiological responses compared to recreational athletes, suggesting enhanced peripheral oxygen extraction.