Recurrence quantification analysis of heart rate variability to detect both ventilatory thresholds

Area of Science:

• Exercise Physiology
• Cardiovascular Physiology
• Non-invasive Physiological Monitoring

Background:

• Determining ventilatory thresholds is crucial for assessing exercise intensity and fitness levels.
• Traditional gas-exchange (GE) methods require specialized equipment and can be inconvenient.
• Recurrence Quantification Analysis (RQA) offers a potential non-invasive alternative for analyzing Heart Rate Variability (HRV) time series.

Purpose of the Study:

• To evaluate the efficacy of RQA of HRV in identifying both aerobic (AerT) and anaerobic (AnT) thresholds.
• To compare the validity of the RQA method against the established GE method across different fitness levels.
• To assess the reliability and agreement of RQA-derived parameters with GE measurements.

Main Methods:

• Thirty young individuals of varying fitness levels performed incremental cycle-ergometer exercise.
• Heart rate (HR), oxygen consumption (VO2), and workload were measured simultaneously using RQA and GE methods.
• Statistical analyses included Repeated Measures ANOVA, Ordinary Least Products (OLP) regression, Typical Percentage Error (TE), and Intraclass Correlation Coefficients (ICC).

Main Results:

• No significant interaction effects between methods and fitness groups were observed for HR, VO2, and workload at either threshold.
• OLP regression revealed strong correlations (r > 0.8) between RQA and GE for all measured variables at both AerT and AnT.
• Excellent ICC values (≥0.85 for AerT, ≥0.90 for AnT) and acceptable TE values indicated high reliability and agreement between the methods.

Conclusions:

• RQA of HRV time series is a valid and reliable method for determining both aerobic and anaerobic ventilatory thresholds.
• The RQA approach demonstrates strong agreement with the gold-standard gas-exchange method.
• RQA presents a practical, non-invasive alternative for ventilatory threshold assessment, particularly when gas analysis is not feasible.