Verification Bout Criteria In The Heat: A Training Status Comparison

Abstract

The use of verification bouts (VRF) to confirm maximal oxygen consumption (V̇O2max) in thermoneutral conditions is well established. Less is known about the utility of VRF in the heat. The impact of a hot environment may affect trained and untrained subjects differently. Data demonstrating the impact of heat on repeat bouts of high-intensity exercise may be useful for individuals performing an unaccustomed activity in the heat. PURPOSE: To compare V̇O2, heart rate (HR), and rating of perceived exertion (RPE) from a graded exercise test (GXT) vs. VRF in trained vs. untrained subjects. METHODS: Aerobically trained (T) (n=10) and untrained (UT) (n=11) college-aged males volunteered. Baseline gastrointestinal temperature (Tgi) and resting V̇O2, RPE, and HR values were collected then subjects rested in a heated chamber (39°C, 31% relative humidity) for 20 min before completing the GXT. Post-GXT, subjects exited the chamber and rested in a thermoneutral room (22°C, 40%RH) until Tgi returned to baseline. Subjects re-entered chamber and repeated pre-GXT procedures prior to VRF. For VRF, subjects warmed-up cycled at 60% maximal wattage (Wmax) from GXT and then cycled at 110% Wmax until exhaustion. V̇O2, HR, and RPE values from the last complete min were used for comparison. A 2 × 2 [(T vs. UT)×(GXT vs. VRF)] mixed-factor ANOVA with Bonferroni post hoc tests and an alpha of 0.05 was used for analysis. RESULTS: V̇O2: trained cyclists V̇O2max was greater than untrained (56.4±8.6 vs. 40.1±5.9 mL·kg-1·min-1, p<0.001); V̇O2 during GXT was greater than VRF for both groups (p=0.013, ηp2=0.29). HR: subjects had significantly higher HR during GXT vs. VRF (T:188vs.178bpm; UT:189vs.181bpm; p<0.001, ηp2=0.74) and HR was not significantly different between groups (p=0.77). RPE: There was a significant trial×training interaction (p=0.04, ηp2=0.21), and a significant main effect for training status with trained cyclists expressing higher RPE than untrained in GXT & VRF(19vs.18; 19vs.17;p=0.002). CONCLUSION: The results indicated that RPE may be tied to V̇O2 more than HR in the heat in trained subjects. V̇O2 during VRF in the heat was less than V̇O2max in all subjects during GXT which may confirm V̇O2max or indicate premature fatigue due to heat. Thus, a VRF may not be necessary for the determination of V̇O2max in the heat for untrained subjects.