In the ever-evolving domain of sports science, the study led by Bas Van Hooren and colleagues explores the correlation properties of heart rate variability (HRV) in the context of the first ventilatory threshold (VT1) and fatigue among runners. Central to this investigation is the Omnical indirect calorimeter, a sophisticated tool that elevates the study’s precision and reliability. This research not only offers new insights into athlete performance but also underscores the burgeoning role of advanced technology in exercise physiology. 

Goals of the Study 

The primary objectives of this study were two-fold: 

  1. To validate the concept of heart rate variability threshold (HRVT) by juxtaposing DFA-a1 values obtained from a consumer-grade chest belt against VT1 measurements derived from the Omnical. This comparison aimed to ascertain the accuracy and utility of HRV in non-fatigued states. 
  1. To examine the influence of acute fatigue on the DFA-a1 and VT1 relationship. This aspect of the study sought to understand the viability of DFA-a1 as an indicator for fatigue-based training prescription, a relatively unexplored area in exercise science. 


The study’s methodological rigor was evident in its comprehensive approach. It involved 14 participants undergoing two distinct treadmill test sessions, designed to simulate both non-fatigued and fatigued physical states. The Omnical indirect calorimeter played a pivotal role, offering precise gas exchange measurements that served as a gold standard for comparing HRV data. The analysis centered on assessing the agreement between oxygen uptake (V̇O2) and heart rate (HR) at VT1, determined through gas exchange, with V̇O2 and HR at a DFA-a1 value of 0.75. Bland-Altman analysis and linear regression were employed for this comparative analysis. 


The study yielded enlightening results. In non-fatigued conditions, there was a close agreement between the DFA-a1 values and VT1 as measured by the Omnical, suggesting HRV’s potential as a reliable marker for exercise intensity demarcation. However, this agreement was notably altered under conditions of fatigue. The results highlighted DFA-a1’s sensitivity to physical stress and its prospective application in devising fatigue-based training regimes. These findings are crucial as they suggest that while DFA-a1 is a valid marker in non-fatigued states, its efficacy is modulated by the athlete’s fatigue levels. 

This graphical representation captures the changes in oxygen uptake (VO2) and heart rate (HR) at two crucial ventilatory thresholds across dual ramp tests. Panels a and c focus on the gas exchange first ventilatory threshold (VT1), while panels b and d concentrate on the heart rate variability threshold (HRVT). The figure is detailed with dots, each signifying individual participant measurements, offering a granular view of the data. Box and whisker elements within the graph highlight the median values and the interquartile ranges, providing insight into the central tendency and spread of the data. Additionally, the distribution plots are included to visually convey the overall spread and arrangement of the data points, giving a comprehensive picture of the variations observed in VO2 and HR across the thresholds. 


This study, leveraging the capabilities of the Omnical indirect calorimeter, makes a substantial contribution to the field of exercise physiology and sports performance. It validates the HRVT concept in non-fatigued conditions and elucidates the dynamic nature of HRV in response to physical stress. The findings emphasize the potential of HRV data, especially DFA-a1, in refining training protocols based on fatigue levels, offering a more personalized and effective approach to athlete training. Furthermore, the study accentuates the need for ongoing advancements in wearable technology to ensure robust, field-applicable solutions in athletic training and performance monitoring. 

Related products 


The Omnical is the most versatile and accurate indirect calorimeter for research purposes on the market. Comprised of state-of-the-art technology using the highest-class precision measurement instruments, it enables customers to perform studies in various research fields. The system is designed to measure energy metabolism ranging from resting metabolism rate (RMR) to sports performance testing (e.g. VO2max tests) with high accuracy. 

How can we help you with your research? 

Maastricht Instruments creates equipment in the field for indirect calorimetry measurements. We provide support for studies, research and measurements alongside our indirect calorimetry products. Consult us about our indirect calorimetry metabolic  cart,  whole room calorimeter  systems or  accelerometry  add-ons. Please  contact us or find more information on our information pages. 


Bas Van Hooren, Bram Mennen, Thomas Gronwald, Bart C. Bongers & Bruce Rogers (2023) Correlation properties of heart rate variability to assess the first ventilatory threshold and fatigue in runners, Journal of Sports Sciences, DOI: 10.1080/02640414.2023.2277034