Figure 2.

Infrared thermography of supraclavicular BAT heat production at cooling and a thermal comfort (TC) state

Subjects (WS, n = 7; C, n = 8) were cooled using a Blanketrol III system by controlling the temperature of circulating water in the blanket. n represents the number of human individuals in each group and is consistent throughout this figure unless otherwise specifically stated.

(A) Water temperature in the blanket during cooling.

(B) Estimate of the subjects’ temperature perception using a VAS score.

(C) Core temperature as estimated by rectal thermometers. On a separate day, subjects were observed during the thermal comfort state protocol.

(D) Water temperature during a thermal comfort state.

(E) Estimate of the subjects’ temperature perception using a VAS score.

(F) Core temperature as estimated by rectal thermometers.

(G) Supraclavicular BAT skin temperature during cooling measured by IRT. The effect of the group and cooling were assessed during time points of 45–105 min. Sidak’s post-test was used to assess differences between the time point of 45 min (thermal comfort state) and the time points during cooling.

(H) Sternum skin temperature during cooling as measured by IRT and analyzed as described in (G).

(I) Supraclavicular BAT skin temperature in relation to the temperature at the sternum in response to cooling. Area under the curve (AUC) between groups is displayed to the right.

(J) Supraclavicular BAT skin temperature as measured by IRT during a thermal comfort state and analyzed as described in (G).

(K) Sternum skin temperature during a thermal comfort state as measured by IRT and analyzed as described in (G).

(L) IRT recording of the temperature changes in response to a thermal comfort state in supraclavicular BAT in relation to the temperature at the sternum. Because of experimental error, measurements were not available for all subjects at every time point. The time points at which data from fewer than three subjects were recorded were excluded.

(M) Representative IRT images of a control subject (upper panel) and a winter swimmer (lower panel). The scale bar represents temperature in °C.

(N) MRI assessing the distance between the activated BAT and the surface of the skin in the area where IRT images were obtained.

Relative IRT values in (I) and (L) were calculated as described in the STAR Methods section. Data are presented as mean ± SD. ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001. See also Figure S1.