The relative influence of body characteristics on humid heat stress response |
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Authors: | G Havenith V G M Luttikholt T G M Vrijkotte |
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Institution: | (1) TNO Human Factors Research Institute, Soesterberg, Kampweg 5, NL-3769 DE, Soesterberg, The Netherlands |
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Abstract: | The present study was designed to determine the relative importance of individual characteristics such as maximal oxygen uptake (
O2max), adiposity, DuBois body surface area (A
D), surface to mass ratio (A
D: mass) and body mass, for the individual's reaction to humid heat stress. For this purpose 27 subjects (19 men, 8 women), with heterogeneous characteristics (
O2max 1.86–5.28 1 · min–1; fat% 8.0%–31.9%; mass 49.8–102.1 kg; A
D 1.52–2.33 m2) first rested (30 min) and then exercised (60 W for 1 h) on a cycle ergometer in a warm humid climate (35°C, 80% relative humidity). Their physiological responses at the end of exercise were analysed to assess their relationship with individual characteristics using a stepwise multiple regression technique. Dependent variables (with ranges) included final values of rectal temperature (T
re 37.5–39.0°C), mean skin temperature (T
sk 35.7–37.5°C), body heat storage (S 3.2–8.1 J · g–1), heart rate (HR 100–172 beat · min–1), sweat loss (397–1403g), mean arterial blood pressure (BPa, 68–96 mmHg), forearm blood flow (FBF, 10.1–33.9 ml · 100ml–1 · min–1) and forearm vascular conductance (FVC = FBF/BPa, 0.11–0.49 ml · 100 ml–1 · min–1 · mmHg–1). The T
re, T
sk and S were (34%–65%) determined in the: main by (
O2max), or by exercise intensity expressed as a percent age of
O2max (%
O2max). For T
re, A
D: mass ratio also contributed to the variance explained, with about half the effect of (
O2max), For T
sk, fat% contributed to the variance explained with about two-third the effect of
O2max. Total body sweat loss was highly dependent (50%) on body size (A
D or mass) with regular activity level having a quarter of the effect of body size on sweat loss. The HR, similar to T
re, was determined by
O2max (48%–51%), with less than half the effect of A
D or A
D :mass (20%). Other circulatory parameters (FBF, BPa, FVC) showed little relationship with individual characteristics ( < 36% of variance explained). In general, the higher the (
O2max), and/or the bigger the subject, the lower the heat strain observed. The widely accepted concept, that body core temperature is determined by exercise intensity expressed as %
O2max and sweat loss by absolute heat load, was only partially supported by the results. For both variables, other individual characteristics were also shown to contribute. |
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Keywords: | Body temperature Sweating Exercise Heat strain Body characteristics |
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