Which common NIRS variable reflects muscle estimated lactate threshold most closely?

Area of Science:

• Exercise Physiology
• Biomedical Engineering
• Sports Science

Background:

• Near-infrared spectroscopy (NIRS) is utilized to estimate muscle lactate threshold (LT).
• Previous research has not identified the optimal NIRS variable for reflecting muscle LT.
• Understanding muscle oxygenation dynamics is crucial for performance assessment.

Purpose of the Study:

• To determine which common NIRS variable best estimates muscle lactate threshold (LT).
• To investigate the relationships between NIRS-derived variables and physiological markers of exercise intensity.
• To identify the most reliable NIRS parameter for assessing muscle metabolic changes.

Main Methods:

• Utilized NIRS to measure changes in deoxyhemoglobin (DeltaHHb), oxyhemoglobin (DeltaO2Hb), and tissue oxygenation index (TOI) during incremental cycling exercise.
• Established inflection points for NIRS variables and blood lactate concentration using regression analysis.
• Correlated NIRS variables with ventilatory threshold (VT), LT, and maximal tissue hemoglobin index (nTHImax).

Main Results:

• Deoxyhemoglobin (DeltaHHb) and TOI were measurable in all subjects; DeltaO2Hb was measurable in most.
• Workload and VO2 at DeltaO2Hb and nTHImax were higher than at VT, LT, DeltaHHb, and TOI.
• DeltaHHb showed the strongest correlations with VT and LT, indicating its efficacy in reflecting muscle deoxygenation and O2 metabolic dynamics.

Conclusions:

• Deoxyhemoglobin (DeltaHHb) is the most effective NIRS variable for estimating muscle lactate threshold (LT).
• NIRS variables provide insights into local muscle perfusion and oxygenation status during exercise.
• DeltaHHb accurately reflects deoxygenation changes and oxygen metabolic dynamics, making it superior for LT estimation.