Improving the Agreement Between the First Heart-Rate-Variability Threshold and the Gas-Exchange Threshold

Area of Science:

• Exercise Physiology
• Cardiovascular Physiology
• Biomedical Engineering

Background:

• The first heart-rate variability (HRV) derived threshold, specifically using detrended fluctuation analysis alpha 1 (DFA a1), has shown inconsistent agreement with the established gas-exchange threshold (GET).
• Existing methods for calculating the first HRV threshold (HRVT1) may not adequately capture individual physiological responses during incremental exercise.

Purpose of the Study:

• To investigate whether a custom method for computing the first HRV threshold (HRVT1c), based on individual HRV characteristics, improves agreement with the gas-exchange threshold (GET).
• To compare the agreement between GET and two methods of determining the first HRV threshold: a standard DFA a1 = 0.75 (HRVT1s) and a custom value (HRVT1c).

Main Methods:

• Fourteen participants completed ramp incremental exercise tests, with simultaneous measurement of gas-exchange variables and RR intervals for HRV analysis.
• The custom HRVT1c was determined using a DFA a1 value midway between the maximum observed during the early ramp phase and 0.5.
• Oxygen consumption (V˙O2) and heart rate (HR) at the GET were compared to those at the HRVT1s and HRVT1c.

Main Results:

• Statistically significant differences were found between GET and HRVT1s for both V˙O2 (25.4 vs 29.8 mL·kg-1·min-1) and HR (131 vs 146 beats·min-1).
• No statistical differences were observed between GET and HRVT1c for V˙O2 (25.4 vs 25.1 mL·kg-1·min-1) or HR (131 vs 132 beats·min-1), with equivalence verified.
• Pearson correlation coefficients between GET and HRVT1 methods ranged from 0.67 to 0.70.

Conclusions:

• The custom-derived first heart-rate variability threshold (HRVT1c) demonstrates significantly stronger agreement with gas-exchange threshold (GET) parameters compared to the standard method (HRVT1s).
• This individualized approach to calculating HRVT1 is recommended for more accurate determination of exercise intensity thresholds based on HRV.