Response

A comparison of thermoregulatory responses to exercise between mass-matched groups with large differences in body fat

“…However, as we were unable to collect a full set of esophageal temperature data, we are unable to determine whether this arose due to a prolonged onset threshold and/or a blunted thermosensitivity. It has also been recently proposed that due to its low conductivity, fat mass may not contribute fully to an individual's "heat sink" (16). It follows that such a mechanism may also explain the greater rise in core temperature in the HI-BF group in the FHP trial.…”

“…Arguably the most important finding of the present study was that the relatively small influence of %BF on core temperature changes during exercise should clearly not be countered by prescribing a fixed H prod in watts per kilogram LBM. This traditionally held notion (16,28) is based on the rationale that during non-weight-bearing exercise (e.g., cycling), fat tissue functions primarily as surplus mass because it is not actively producing heat, so it is assumed that a rate of heat production based on lean body mass (i.e., metabolically active tissue) would remove any confounding influence of body fat differences. However, the LBM trial shows that large systematic differences in core temperature changes, and sweating responses, are generated by the much greater H prod in watts per kilogram TBM (8) and E req (15,24,38) in the LO-BF group.…”

“…While the lower specific heat of fat (2.97 kJ·kg Ϫ1 ·°C Ϫ1 ) relative to lean mass (3.66 kJ·kg Ϫ1 ·°C Ϫ1 ) should theoretically lead to a greater temperature change for a given amount of heat energy stored inside the body, a 20% difference in fat mass only leads to a minor difference (ϳ3-5%) in mean specific heat of the total body (17). However, it is also possible that due to its low thermal conductivity, fat mass may not fully contribute to the total body mass "heat sink" (16). The insulative properties of subcutaneous fat could also impair skin surface heat loss (3), but probably only in cooler environments (19).…”

“…It has been proposed that the supposed confounding influence of %BF on thermoregulatory responses can be eliminated by selecting an exercise intensity that elicits the same H prod per unit lean body mass (W/kg LBM) (16). However, if %BF does not substantially influence the maintenance of core body temperature during exercise, such an approach would inadvertently lead to systematically greater sweat rates in lean individuals due to a greater E req (8,15,24), and greater changes in core temperature due to a greater H prod per kilogram total body mass (8).…”