Fig 1.
Study protocol.
Fig 2.
Mean time of the study periods (A), and room-air and cooling vest temperature (B). Values are mean ± standard deviation. ST: shivering threshold, WP: warm period, 31% and 64%: percentage of the individual’s time exposed to cold until shivering occurred.
Fig 3.
Resting energy expenditure (A), respiratory quotient (B) and substrate metabolism (C) across study periods. Values are mean ± standard deviation (n = 10). Repeated measures analysis of variance was performed, using Bonferroni post-hoc tests for pairwise comparisons. Common letters show significant differences (P≤0.05) between two specific periods. CHO: carbohydrates, REE: resting energy expenditure, RQ: respiratory quotient, ST: shivering threshold, WP: warm period, 31% and 64%: percentage of the individual’s time exposed to cold until shivering occurred.
Fig 4.
Skin temperature and body gradients across study periods.
Panel (A): skin temperature, Panel (B): proxies of peripheral vasoconstriction in both arms, Panel (C): body and supraclavicular skin temperature gradients. Values are mean ± standard deviation. Repeated measures analysis of variance was performed, using Bonferroni post-hoc tests for pairwise comparisons. Common letters show significant differences (P<0.05) between two specific periods. Symbol * shows significant differences among all periods (P<0.05). ST: shivering threshold, WP: warm period, 31% and 64%: percentage of the individual’s time exposed to cold until shivering occurred.
Fig 5.
Thermal comfort perception measured by visual analogue scales across study periods.
Visual analogue scales measured thermal comfort from “no cold at all” (= 0 mm) to “maximum tolerable cold” (= 100 mm). Values are mean ± standard deviation (n = 11). Repeated measures analysis of variance was performed, using Bonferroni post-hoc tests for pairwise comparisons. Common letters show significant differences between two specific periods (P<0.05). Symbol * shows significant differences among all time periods (P<0.05). ST: shivering threshold, WP: warm period, 31% and 64%: percentage of the individual’s time exposed to cold until shivering occurred.
Fig 6.
Electrical muscle activity (mV) and burst shivering rate (min-1) of eight different muscles across study periods.
Panel (A): root mean square, Panel (B): burst shivering rate. Values are mean ± standard deviation (n = 6). Repeated measures analysis of variance (Bonferroni post-hoc tests) and Friedman test (adjusted significance) were respectively performed for EMG RMS and EMG BSR. Common letters show significant differences between periods (P < 0.05). BSR: burst shivering rate, RMS: root mean square, ST: shivering threshold, WP: warm period, 31% and 64%: percentage of the individual’s time exposed to cold until shivering occurred.
Fig 7.
Tissue saturation index (%) and relative changes in the concentration of total haemoglobin (ΔtHb), oxy-haemoglobin (ΔO2Hb), and deoxy-haemoglobin (ΔHHb) in the abdominal and forearm regions across study periods.
Panel (A): abdominal region, Panel (B): forearm region. Values are mean ± standard deviation (n = 9). Repeated measures analysis of variance was performed, using Bonferroni post-hoc tests for pairwise comparisons. Common letters show significant differences between two specific periods (P<0.05). ST: shivering threshold, WP: warm period, 31% and 64%: percentage of the individual’s time exposed to cold until shivering occurred.
Fig 8.
Frequency domain parameters of heart rate variability across study periods.
Panel (A): absolute power, Panel (B): normalized power, Panel (C): low frequency—high frequency ratio. Values are mean ± standard deviation (n = 7). Repeated measures analysis of variance was performed, using Bonferroni post-hoc tests for pairwise comparisons. No significant differences were found across study periods (P>0.05). ST: shivering threshold, WP: warm period, 31% and 64%: percentage of the individual’s time exposed to cold until shivering occurred.