Resting metabolic rate (RMR) should be measured in the thermoneutral zone (TNZ). Forearm to fingertip skin temperature gradients (FFG) could serve as an objective measure of this pre-condition.SUBJECTS/METHODS:
Eighty-six adult Australians were studied at 25 °C in a temperature-controlled chamber. Measurements of overnight fasted RMR, respiratory quotient (RQ) and FFG were complemented by clinical biochemistry. McAuley's Index of insulin sensitivity (McA_ISI) and presence of metabolic syndrome was determined. Physical activity was estimated from the short version of the International Physical Activity Questionnaire. Fat mass (FM) and fat-free mass (FFM) were obtained from dual-energy x-ray absorptiometry. Twenty-nine participants were assessed for changes in RMR (ΔRMR), RQ (ΔRQ) and FFG (ΔFFG) following a 6-month free-living period. Multiple linear regression analyses of RMR and RQ on FFG, and of ΔRMR and ΔRQ on ΔFFG were conducted after controlling for 12 known determinants of energy metabolism.RESULTS:
There were wide between-subject variations in unadjusted FFG ranging from - 4.25 to +7.8 °C. The final parsimonious model for cross-sectional observations of RMR included age, FM, FFM, McA_ISI and FFG (β = 63 kJ/d (95% confidence interval (CI): 14.2, 112.1, P = 0.012)). However, FFG was unrelated to RQ. In the longitudinal cohort, adjusted ΔRMR significantly associated only with ΔFFG (β = 100 kJ/d (95% CI: 10.3, 189.1; P = 0.030)), and adjusted ΔRQ associated with ΔFFG (-0.003 (95% CI: - 0.005, 0.0002, P = 0.038)), age and McA_ISI.CONCLUSIONS:
Sizeable between-subject variations in FFG at 25 °C were associated with RMR and RQ. Monitoring FFG may serve as an objective assessment of the TNZ during RMR measurements.