Beyond the second ventilatory threshold: The prevalence and reliability of a second respiratory compensation point and third ventilatory threshold.

Respiratory data obtained from cardiopulmonary exercise testing is commonly used to study ventilatory thresholds (VT). Traditionally, these thresholds correspond to two physiological transition points where the cardiorespiratory and metabolic systems shift in response to increasing exercise. However, the terminology and methodology used to describe submaximal thresholds is contradictory. The anaerobic threshold, second ventilatory threshold (VT2), or respiratory compensation point (RCP) are different terms that describe the second threshold. Despite many papers using this terminology interchangeably, different methods exist to identify them. Recent literature suggests that RCP overestimates VT2 in elite athletes, suggesting a third ventilatory threshold (VT3). Study one explored whether RCP overestimates VT2 and if a third threshold, beyond the second transition point, can be identified within cyclists. Overall VT2 and RCP1 reflected the same physiological transition point, both occurring around 70% peak power output (PPO). Furthermore, VT3/RCP2 was identified at ~90% PPO in 72% of participants. Participants presenting VT3/RCP2 were younger (p=0.01) and demonstrated a longer time to exhaustion, power-to-weight ratio and PPO (p=0.01-0.02), and a moderate effect size (ES) for BMI and V̇O2Peak(ES=0.5). Study two reported the interrater and test re-test reliability of all the thresholds during cycling and running. Interrater reliability reported excellent interclass correlation (ICC) (r=0.96-1.00) across all thresholds and sporting modalities. There was moderate-excellent test, re-test reliability between visits across all thresholds and modalities (r=0.71-0.97), and excellent ICC for VT3/RCP2 (r=0.91-0.97). Overall VT3/RCP2 was repeatedly identified within 6 of 7 cyclists and 2 of 13 runners. Overall, this study expands on the traditional understanding of VT, demonstrating that a third threshold can be confidently and repeatedly identified within cycle tests. The prevalence of a third threshold is likely to be associated with athletes of a higher trained status. However, the prevalence of VT3/RCP2 during treadmill tests is not as clear and requires further exploration. Keywords: ventilatory threshold, cycling, running, performance, exercise.