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Circadian Rhythm Does Not Alter the Sweating Response to Exercise in Thermoneutral and Warm Ambient Temperatures
Author(s) -
Ravanelli Nicholas,
Imbeault Pascal,
Jay Ollie
Publication year - 2018
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2018.32.1_supplement.590.1
Subject(s) - thermoregulation , chemistry , circadian rhythm , sweat , relative humidity , medicine , zoology , core temperature , heart rate , cycle ergometer , endocrinology , blood pressure , biology , meteorology , physics
The present study sought to determine whether the diurnal fluctuation in core temperature alters the sweating response to exercise in thermoneutral (23°C) and warm (33°C) environments. Six healthy males exercised on a semi‐recumbent ergometer at a fixed evaporative requirement for heat balance (200W/m 2 ) for 60 min at two different times of day and two ambient temperatures matched for absolute humidity (1.3 kPa); i) 0800h/23°C, ii) 0800h/33°C, iii) 1600h/23°C, and iv) 1600h/33°C. Esophageal temperature (T es ), mean body temperature (T b ), local sweat rate (LSR) measured at the arm and upper back, and whole body sweat loss (WBSL) were measured. Resting absolute T es was higher at 1600h compared to 0800h at 23°C (0800h: 36.7±0.2°C, 1600h: 36.9±0.2°C; P=0.04) and 33°C (0800h: 36.6±0.2°C, 1600h 36.9±0.2°C; P=0.005). Similarly, end‐exercise (steady‐state) absolute T es was higher at 1600h relative to 0800h at 23°C (0800h: 37.4±0.2°C, 1600h: 37.6±0.2°C; P=0.04) and 33°C (0800h: 37.0±0.2°C, 1600h 37.2±0.2°C; P=0.01). However the change in T es was similar irrespective of the time of day at both 23°C (0800h: 0.7±0.1°C, 1600h: 0.7±0.2°C; P=0.37) and 33°C (0800h: 0.4±0.1°C, 1600h: 0.3±0.1°C; P=0.35). Further, mean steady‐state LSR of arm and back after 60 min of exercise was similar irrespective of time at both 23°C (0800h: 0.66±0.06 mg/cm 2 /min, 1600h: 0.65±0.13 mg/cm 2 /min; P=0.74) and 33°C (0800h: 0.62±0.11 mg/cm 2 /min, 1600 h: 0.58±0.11 mg/cm 2 /min, P=0.50). Likewise, WBSL at steady‐state (46 to 60 min) was similar between morning and afternoon trials at 23°C (0800h: 156±28 g, 1600h: 162±36 g; P=0.38) and 33°C (0800h: 147±29 g, 1600h: 158±34 g, P=0.55). While sweating commenced prior to exercise in 33°C, the onset threshold for sweating occurred at a higher T b at 1600h compared to 800h at 23°C (0800h: 35.6±0.1°C, 1600h 35.9±0.2°C; P=0.03), however the change in T b was similar at 23°C regardless of time of day (0800h: 0.14±0.07°C, 1600h 0.17±0.12°C; P=0.47). Lastly, sudomotor thermosensitivity (LSR‐T b ) was similar at both 23°C (0800h: 0.80±0.26 mg/cm 2 /min/°C, 1600h: 0.82±0.30 mg/cm 2 /min/°C; P=0.80) and 33°C (0800h: 0.81±0.18 mg/cm 2 /min, 1600h: 0.90±0.40 mg/cm 2 /min, P=0.87). Taken together, preliminary data suggests the difference in absolute core temperature (~0.3°C) associated with diurnal fluctuation does not alter the sweating response at a fixed evaporative requirement for heat balance in both thermoneutral and warm conditions. Support or Funding Information N.R. was supported by an NSERC Postgraduate Scholarship‐Doctoral and a University of Ottawa Excellence Scholarship. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .