The running heat tolerance test is a suitable protocol for between-group comparisons of heat tolerance in females: 6th International Conference on the Physiology and Pharmacology of Temperature Regulation, Slovenia

Introduction: The running heat tolerance test (RHTT) is a reliable protocol to quantify individual heat tolerance, supporting the use of the RHTT when using a repeated measures design (Mee et al., 2015). However, biophysical factors related to heat production (Hprod) and body mass (BM) predominantly influence change in rectal temperature (∆Tre) (Cramer and Jay, 2014), questioning the use of the RHTT when using a between-subjects design. The present study tested the hypothesis that when Hprod is matched between groups with large differences in BM and V̇O2 peak, individual variation in ∆Tre during the RHTT is eliminated.
Methods: Twenty-eight female participants performed a RHTT (9km.hr-1, 2% gradient, for 30-min, in 40°C and 40% RH). Participants were grouped for analyses according to BM [low (N = 7): 49 ± 4 kg; high (N = 7): 72 ± 2 kg] and V̇O2 peak [low (N = 7): 41 ±2 mL.kg-1.min-1; high (N = 7): 57 ± 5 mL.kg-1.min-1]. Independent sample t-tests were used for analyses.
Results: The RHTT demonstrated similar Hprod in participants of high (10.9 ± 2.6 W.kg-1) and low BM (10.5 ± 1.7 W.kg-1; p = 0.694), resulting in similar ∆Tre (high BM: 2.0 ± 0.4°C; low BM: 1.7 ± 0.2°C; p = 0.100). The RHTT demonstrated similar Hprod in participants of high (10.6 ± 2.2 W.kg-1) and low V̇O2 peak (10.7 ± 2.4 W.kg-1; p = 0.909), resulting in similar ∆Tre (high V̇O2 peak 1.8 ± 0.4°C; low V̇O2 peak: 2.0 ± 0.4°C; p = 0.360).
Conclusions: These findings provide evidence that the exercise intensity administered during the RHTT equates to similar Hprod (W.kg-1), permitting unbiased independent group comparisons and supporting the use of the RHTT when using a between-subjects design. These interpretations are limited to a female population, further consideration should be made when using male participants.

References
Cramer MN and Jay O (2014) Selecting the correct exercise intensity for unbiased comparisons of thermoregulatory responses between groups of different mass and surface area. Journal of Applied Physiology 116(9): 1123–32.
Mee J, Doust J and Maxwell N (2015) Repeatability of a running heat tolerance test. Journal of Thermal Biology 49-50: 91–97.