Thresholds Derived From Muscle NIRS Signal, Heart Rate Variability, and Ventilatory Parameters During an Incremental...

Area of Science:

• Exercise Physiology
• Sports Science
• Biomedical Engineering

Background:

• Accurate determination of physiological thresholds is crucial for optimizing athletic performance and training.
• Ventilatory thresholds (VT) are established markers, but alternative non-invasive methods are being explored.
• Muscle near-infrared spectroscopy (NIRS) and heart rate variability (HRV) offer potential for real-time physiological monitoring.

Purpose of the Study:

• To compare thresholds derived from NIRS and HRV with traditional ventilatory thresholds (VT1 and VT2) during maximal incremental cycling.
• To evaluate the agreement and potential application of NIRS- and HRV-derived parameters for exercise intensity prescription.

Main Methods:

• Twenty trained male cyclists underwent a maximal incremental cycling test.
• Continuous monitoring included breath-by-breath gas analysis, muscle NIRS (O2HbT, HHbT, TSIT), HRV (SD1T, SD2T), and heart rate (HR).
• The DMAX method was used for NIRS-derived thresholds; VT1, VT2, and HR deflection point were also identified.

Main Results:

• No significant differences were found between VT1 and NIRS-derived O2HbT, nor between VT1 and HRV-derived SD1T/SD2T when expressed as power output.
• VT2 showed no significant difference compared to NIRS-derived TSIT.
• However, substantial inter-individual variability (limits of agreement up to ±107 W) was observed, indicating limited precision for individual prescription.

Conclusions:

• NIRS and HRV parameters show some correlation with ventilatory thresholds but exhibit significant inter-individual variability.
• These methods may complement, but should not substitute, traditional ventilatory threshold assessments for precise exercise prescription.
• Further research is needed to refine these non-invasive techniques for reliable individual application in sports science and clinical settings.