Measurement and prediction of peak shivering intensity in humans

Abstract

Prediction equations of shivering metabolism are critical to the development of models of thermoregulation during cold exposure. Although the intensity of maximal shivering has not yet been predicted, a peak shivering metabolic rate (Shiv_peak) of five times the resting metabolic rate has been reported. A group of 15 subjects (including 4 women) [mean age 24.7 (SD 6) years, mean body mass 72.1 (SD 12) kg, mean height 1.76 (SD 0.1) m, mean body fat 22.3 (SD 7)% and mean maximal oxygen uptake (V˙O_2max) 53.2 (SD 9) ml O₂ · kg⁻¹ · min⁻¹] participated in the present study to measure and predict Shiv_peak. The subjects were initially immersed in water at 8°C for up to 70 min. Water temperature was then gradually increased at 0.8 °C · min⁻¹ to a value of 20 °C, which it was expected would increase shivering heat production based on the knowledge that peripheral cold receptors fire maximally at approximately this temperature. This, in combination with the relatively low core temperature at the time this water temperature was reached, was hypothesized would stimulate Shiv_peak. Prior to warming the water from 8 to 20 °C, the oxygen consumption was 15.1 (SD 5.5) ml · kg⁻¹ · min⁻¹ at core temperatures of approximately 35 °C. After the water temperature had risen to 20 °C, the observed Shiv_peak was 22.1 (SD 4.2) ml O₂ · kg⁻¹ · min⁻¹ at core and mean skin temperatures of 35.2 (SD 0.9) and 22.1 (SD 2.2) °C, respectively. The Shiv_peak corresponded to 4.9 (SD 0.8) times the resting metabolism and 41.7 (SD 5.1)% of V˙O_2max. The best fit equation predicting Shiv_peak was Shiv_peak (ml O₂ · kg⁻¹ · min⁻¹)=30.5 + 0.348 ×V˙O_2max (ml O₂ · kg⁻¹ · min⁻¹) − 0.909 × body mass index (kg · m⁻²) − 0.233 × age (years); (P=0.0001; r ²=0.872).