Verification Testing to Confirm V˙O2max in a Hot Environment

Abstract

Verification tests to confirm graded exercise test (GXT) V˙O2max 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 V˙O2max 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 V˙O2max (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 V˙O2max 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 V˙O2max 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 V˙O2max 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.

Verification Phase Confirms V̇O2max in a Hot Environment in Sedentary Untrained Males

“…Rest between the GXT and the verification phase test was anchored to the time required for T gi restoration to baseline to minimize exercise-heat stress carryover effects on subsequent high intensity aerobic performance (35). T gi recovery after heavy exercise in the heat may require four to five times longer than the duration of exercise (36), an estimation in line with previous data (17) and within rest period ranges used in previous verification phase studies (37). Our verification phase protocol occurred in the heat, was similar to previous studies (17,19) and in line with recommended practices (3,17,21).…”

“…In the only study to evaluate verification phase testing in the heat, just 25% of trained cyclists demonstrated a VO 2 plateau (e.g., VO 2max ) during a GXT. The verification phase confirmed VO 2max in 92% of the cases (17). However, it is unknown whether sedentary individuals can reproduce similar VO 2max confirmation rates as trained cyclists in the heat.…”

“…Exclusionary criteria were presence of metabolic, cardiovascular, or pulmonary disease; lower extremity orthopedic injury; or exertional heat illness within the past year. This sample size is sufficient to detect a 5% difference in V̇O 2max using a two-tailed dependent t -test (α = 0.05; statistical power = 0.80) assuming a mean V̇O 2max of 45 ± 7 mL·kg −1 ·min −1 and strong correlation (0.93) (17). The university institutional review board approved study procedures (no.…”

“…We used equivalence hypothesis testing to assess whether preexercise T gi and BLa as well as V̇O 2max values from the GXT and verification phase were statistically equivalent (39). It was essential to determine if T gi and BLa were statistically equivalent before testing to assess whether thermal strain and acidosis carryover from the GXT were present, which may influence verification phase responses (17,26). For V̇O 2max , we defined our upper and lower equivalence boundaries from historical thresholds for V̇O 2 plateau (±2.1 mL·kg −1 ·min −1 ) (40) consistent with others (41), clinically meaningful changes in T gi (±0.55°C) (42), and steady-state metabolic measurements (BLa ±10% of pre-GXT) (43).…”

“…Substantial evidence indicates that graded exercise tests (GXT) underestimate VO 2max in sedentary individuals and infrequently exhibit a VO 2 plateau (6)(7)(8)(9)(10)(11)(12)(13)(14) necessitating alternative strategies to confirm VO 2max . Traditional secondary criteria (heart rate [HR], blood lactate [BLa], RER, and RPE) (15) and even the new age-dependent secondary criteria (16) fail to consistently identify VO 2max in the absence of a VO 2 plateau (5,7,14,17). Alternatively, given sufficient exercise duration, a supramaximal verification phase after GXT enables observation of a VO 2 plateau, the primary criterion for VO 2max (i.e., a leveling or decrease in VO 2 with increased work rate [18]), even in sedentary populations (6)(7)(8)(10)(11)(12)(13)19,20).…”