Time-based V-slope for determination of anaerobic threshold

Area of Science:

• Exercise Physiology
• Cardiopulmonary Exercise Testing
• Biomedical Engineering

Background:

• The V-slope (VS) method is standard for noninvasive anaerobic threshold (AT) determination, often supplemented by ventilatory equivalent (VEQ) and end-tidal (ET) methods.
• A key limitation is the differing x-axes: VS plots VCO2 vs. VO2, while VEQ and ET use exercise time.
• This discrepancy complicates direct comparison and integrated analysis of these AT detection methods.

Purpose of the Study:

• To develop a time-based V-slope (VS) graph that aligns VS, VEQ, and ET methods on a common time axis.
• To enable a unified graphical representation for AT detection.
• To improve the reliability and comparability of noninvasive AT determination.

Main Methods:

• A novel 'd' method was developed, plotting the difference between measured VCO2 and VCO2 on the R=1 line against time.
• This time-based VS graph aligns the 'd' method with VEQ and ET on the exercise time axis.
• Data from 127 subjects undergoing maximal exercise testing were analyzed, with AT assessed by 'd', VS, VEQ, and ET in a blinded manner.

Main Results:

• The 'd' method identified AT significantly earlier than the conventional VS method (p < 0.001).
• The coefficient of repeatability (CR) for 'd' (117 mL/min) was lower than for VS (115 mL/min), VEQ (152 mL/min), and ET (175 mL/min), indicating improved reliability.
• The mean squared difference for the 'd' method was significantly smaller than other methods, confirming enhanced reliability.

Conclusions:

• The time-based V-slope ('d' method) effectively aligns multiple AT detection methods on a single time axis.
• This alignment facilitates precise comparison and enhances the reliability of AT detection, likely due to a clearer breakpoint identification against a flat baseline.
• The 'd' method offers a more reliable and earlier identification of AT compared to conventional VS, VEQ, and ET methods.