The relative influences of anthropometric measures, aerobic fitness, pedometer readings and microclimate temperatures in daily life on heat and cold responses of older men

Abstract

The present study was designed to examine the relative influence of calendar age, anthropometric measures, such as percentage body fatness (%fat) and surface area-to-weight ratio (Ad/Wt), maximal oxygen uptake (VO_2max), pedometer readings (PR) and microclimate temperatures in daily life on thermoregulatory responses of older men to heat and cold stress. During 60-min heat exposures [by placing the lower legs and feet in a 42°C water bath under a warm condition (35°C, 45% rh) ] in summer, final rectal temperature (T_re), whole body sweating rate (M_sw), M_sw/ΔT_re, and final mean bloodpressure (MBP) were closely related to PR. Final skin blood flow and cutaneous vascular conductance on the thigh were mainly affected by VO_2mx. Final mean skin temperature (T_sk) and the thigh sweating rate (T_msw) were mainly influenced by age and Ad/Wt, respectively. PR had a secondary influence on T_Sk and T_msw, age a secondary influence on M_sw, M_sw/ΔT_re and MBP, and thirdly %fat had an influence on M_sw/ΔT_re. A similar tendency was observed in summer, although the parameters of heat responses related to PR were decreased. During 60-min cold exposures (12°C, 45% rh) in winter, VO_2max had significant influence on final T_sk, metabolic heat production (M), dry heat loss (DHL), respiratory heat loss (RHL), and skin thermal conductance, and PR affected on heart rate. The %fat was a secondary factor for T_sk and DHL, Ad/Wt a secondary factor for M and RHL, and also VO_2max a secondary factor for final heart rate, respectively. Similar relations were also found for the summer responses to cold stress (17°C, 45% rh) . The PR had significant negative correlations with microclimate temperatures on the chest (spring), upper arm (spring and summer) and back (winter) in daily life. It was concluded that thermoregulatory responses of older men to heat and cold were mainly influenced by pedometer readings reflecting exercise habits and aerobic fitness, together with secondary effects of calendar age and anthropometric factors.