Verification Phase Confirms VO2maxin a Hot Environment in Sedentary Untrained Males

The verification phase is becoming the norm for confirming VO2max during a graded exercise test (GXT), but the use of such testing in untrained participants in the heat remains unknown. Purpose This study aimed to assess the VO2 uptake obtained during a GXT and subsequent verification phase in untrained participants in a hot environment. Methods Twelve sedentary males completed a GXT followed by a biphasic supramaximal-load verification phase in a hot environment (39°C, 32% relative humidity). Rest between tests occurred in a temperate chamber and lasted until gastrointestinal temperature returned to baseline. Results Mean verification phase VO2max (37.8 ± 4.3 mL·kg-1·min-1) was lower than GXT (39.8 ± 4.1 mL·kg-1·min-1; P = 0.03) and not statistically equivalent. Using an individualized analysis approach, only 17% (2/12) of participants achieved a VO2 plateau during the GXT. Verification phase confirmed GXT VO2max in 100% of participants, whereas the traditional and the new age-dependent secondary VO2max criteria indicated GXT VO2max achievement at much lower rates (8/12 [67%] vs 7/12 [58%], respectively). Correlational indices between GXT and verification phase VO2max were strong (intraclass correlation coefficient = 0.95, r = 0.86), and Bland-Altman analysis revealed a low mean bias of -2.1 ± 1.9 mL·kg-1·min-1 and 95% limits of agreement (-5.8 to 1.7 mL·kg-1·min-1). Conclusions Very few untrained males achieved a VO2 plateau during GXT in the heat. When conducting GXT in a hot condition, the verification phase remains a valuable addition to confirm VO2max in untrained males.