Evidence of a double anaerobic threshold in healthy subjects

Abstract

Aims The anaerobic threshold (AT) is an important cardiopulmonary exercise test (CPET) parameter both in healthy and in patients. It is normally determined with three approaches: V-slope method, ventilatory equivalent method, and end-tidal method. The finding of different AT values with these methods is only anecdotic. We defined the presence of a double threshold (DT) when a ΔVO2 > 15 mL/min was observed between the V-slope method (met AT) and the other two methods (vent AT). The aim was to identify whether there is a DT in healthy subjects. Methods and results We retrospectively analysed 476 healthy subjects who performed CPET in our laboratory between 2009 and 2018. We identified 51 subjects with a DT (11% of cases). Cardiopulmonary exercise test data at rest and during the exercise were not different in subjects with DT compared to those without. Met AT always preceded vent AT. Compared to subjects without DT, those with DT showed at met AT lower carbon dioxide output (VCO2), end-tidal carbon dioxide tension (PetCO2) and respiratory exchange ratio (RER), and higher ventilatory equivalent for carbon dioxide (VE/VCO2). Compared to met AT, vent AT showed a higher oxygen uptake (VO2), VCO2, ventilation, respiratory rate, RER, work rate, and PetCO2 but a lower VE/VCO2 and end-tidal oxygen tension. Finally, subjects with DT showed a higher VO2 increase during the isocapnic buffering period. Conclusion Double threshold was present in healthy subjects. The presence of DT does not influence peak exercise performance, but it is associated with a delayed before acidosis-induced hyperventilation.

The double anaerobic threshold in heart failure: MECKI score database overview

“…This is different from that observed in healthy subjects, where DT was present in a similar percentage in both sexes, respectively, 10% of women and 11% of men. 11 As in normal subjects, vent AT always followed met AT. The gap between met AT and vent AT is significant both considering VO 2 and Watts, respectively, 221 (129; 319) mL/min and 20 (14; 29) W. Of note, due to the intrinsic variability of VO 2 changes during exercise in HF patients, to define DT, we utilized a minimum ΔVO 2 100 mL/min between met AT and vent AT.…”

“…The analysed population that belongs to the MECKI score data set consists of HF patients with reduced LVEF in stable medical condition. In this setting, DT was unrelated to exercise performance limitation but it was more frequent than in healthy subjects, which was identified in 11% of cases 11 . Additionally, there was a gender difference: specifically, in HF patients, DT is more frequent in women than in men, being 51% and 42%, respectively.…”

“…We defined the presence of a divergence between the V‐slope and ventilation‐derived methods (>100 mL/min) with the term of DT. We formerly named the AT detected by V‐slope method as metabolic AT (met AT) and the AT identified by ventilation‐derived methods as ventilation AT (vent AT) 11 …”

“…We formerly named the AT detected by V-slope method as metabolic AT (met AT) and the AT identified by ventilation-derived methods as ventilation AT (vent AT). 11 All other CPET parameters were calculated and reported as standard. 8 Specifically, peak VO 2 was reported as the highest recorded VO 2 values (average of 20 s), the oxygen pulse (O 2 -pulse) as VO 2 over heart rate, and the VE/VCO 2 was determined as the slope of the linear relationship between VE and VCO 2 between the second minute of loaded exercise and the respiratory compensation point.…”

“…The first approach is independent from ventilation, while the other two are affected by the ventilatory response to the extra production of carbon dioxide (VCO 2 ) that occurs during exercise above AT. The possibility of a divergence between the V‐slope method, and the other two methods, defined as double threshold (DT), has been reported initially by an anecdotal case report and recently in ≈10% of cases in healthy individuals 11,12 . A delay in the chemoreceptor response has been suggested as DT leading causes 11 .…”