Assessment of the Heart Rate Deflection Point in Athletes for a Non-Invasive Determination of the Anaerobic Threshold: A Systematic Review

Objectives
This study analyzed the systematic bias, limits of agreement (LoA), and association between the anaerobic threshold (AT) and the heart rate deflection point (HRDP) in athletes.

Methods
A systematic search in EBSCOhost, PubMed, and Scopus was performed to identify studies analyzing AT (via blood lactate or gas exchange) and HRDP in athletes. Specific participant characteristics, exercise protocols, and analytical procedures were recorded. A random-effects meta-analysis evaluated agreement and bias between HRDP and AT. Systematic bias between AT and HRDP was assessed for heart rate (beats/min), running speed (km/h), and power output (W). Furthermore, meta-regression analysis was computed by considering the design of exercise protocols as well as methods applied to examine the AT (i.e., second lactate or ventilatory threshold), and the HRDP (i.e., mathematical detection or. visual analysis) as potential moderators.

Results
Twenty-five studies were selected, covering athletes such as runners, cyclists, mountain runners, and rowers. Significant systematic bias was found in heart rate (2.9 beats/min) and running speed (0.7 km/h), but not in power output (4.2 W). Wide limits of agreement were noted across all metrics, and the exercise protocol significantly influenced bias in speed. Methods applied to examine the AT and the HRDP did not influence the systematic bias between exercise thresholds.

Conclusion
Significant bias, wide LoA, and large estimation errors suggest HRDP is not reliable for non-invasive AT estimation in athletes. Standardized protocols and further exploration of population-specific moderators are necessary to enhance its utility as a practical tool for monitoring training adaptations.