hand, a fixed H prod in W should be used to compare absolute whole-body sweat rates (e.g. in L/h) between groups with different body sizes provided sweating efficiency (i.e. the amount of secreted sweat that evaporates from the skin) is not different. In light of this, we offer an alternative interpretation of the data presented by Adams et al. (2014).The obese group in the study by Adams et al. (2014) was more than 23 kg heavier than the non-obese group. Therefore, their trials eliciting fixed rates of H prod of 300 W (FHP trial) and 175 W/m 2 (BSA trial) would have both yielded a H prod relative to total body mass that was lower by 1.8 W/ kg (FHP trial; obese 3.9 W/kg, non-obese 5.7 W/kg) and 1.2 W/kg (BSA trial; obese 4.1 W/kg, non-obese 5.3 W/kg) in the obese group. Indeed, it has been previously demonstrated that a difference in H prod of this magnitude is sufficient to lead to significantly different changes in rectal temperature (Cramer and Jay 2014). Nonetheless, Adams et al. (2014) reported similar changes in core temperature between groups in both trials, potentially indicating that either, (1) heat dissipation may have actually have been inhibited in the obese group; or (2) a lower heat storage was required for a given change in their core temperature secondary to a lower specific heat capacity in the obese group.Exercise performed at a fixed H prod relative to BSA (i.e. in W/m 2 ) is best prescribed to compare local sweat rate responses (Cramer and Jay 2014), which were not measured in the present study (Adams et al. 2014). However, the FHP trial does potentially permit a comparison of wholebody sweat rates, and therefore the potential for heat dissipation, between obese and non-obese groups. The absolute evaporative heat balance requirement (E req , in W) would have been similar, despite a slightly greater absolute dry heat gain from the 40 °C environment in the obese group by virtue of their greater BSA; and under the conditions To the Editor A recent publication by Adams et al. (2014) reported similar core and skin temperature responses between two groups of obese (77.5 kg, 43.5 % body fat) and non-obese (53.7 kg, 26.3 % body fat) females cycling at fixed absolute (in W) and relative (to body surface area; in W/m 2 ) rates of metabolic heat production. The authors concluded that more body fat in young females does not contribute to a greater heat strain. However, recent evidence demonstrates that the change in core temperature during exercise is determined by the rate of metabolic heat production (H prod ) per unit body mass (in W/kg) (Cramer and Jay 2014); and under conditions that permit the complete evaporation of sweat from the skin surface, whole-body sweat losses are determined by the absolute evaporative requirement for heat balance (E req , in W) (Gagnon et al. 2013), which is primarily driven by absolute H prod . It follows that when comparing changes in core temperature between two groups of dissimilar mass, such as in the present study, a fixed H prod in W/kg should be used to avoid expe...