Verification tests to confirm graded exercise test (GXT) VO2max are growing in popularity, but the validity and reliability of such testing in the heat remains unknown. Purpose This study aimed to evaluate the validity and reliability of a verification test to confirm GXT VO2max in a hot environment. Methods Twelve recreationally trained cyclists completed a two-test protocol that included a GXT progressing 20 W·min-1 followed by a biphasic supramaximal-load verification test (1 min at 60% increasing to 110% maximal GXT wattage until failure) in a hot environment (39°C, 32% relative humidity). Rest between tests occurred in a thermoneutral room and was anchored to the duration required for gastrointestinal temperature to return to baseline. Results Mean verification test VO2max (51.3 ± 8.8 mL·kg-1·min-1) was lower than GXT (55.9 ± 7.6 mL·kg-1·min-1, P = 0.02). Verification tests confirmed GXT VO2max in 92% of participants using individual analysis thresholds. Bland-Altman analysis revealed a sizable mean bias (-4.6 ± 4.9 mL·kg-1·min-1) with wide 95% limits of agreement (-14.0 to 5.0 mL·kg-1·min-1) across a range of VO2max values. The high coefficient of variation (9.6%) and typical error (±3.48 mL·kg-1·min-1) indicate potential issues of test-retest reliability in the heat. Conclusions Verification testing in a hot condition confirmed GXT VO2max in virtually all participants, indicating robust utility. To enhance test-retest reliability in this environment, protocol recommendations for work rate and recovery between tests are provided.
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