T underestimated and U consistently perceived their physiological strain, as defined by PhSI, in accordance with the measured increases in core temperature and heart rate throughout an exposure to uncompensable exercise-heat stress.

The development of three dimensional laser scanning technology and sophisticated graphics editing software have allowed an alternative and potentially more accurate determination of body surface area (BSA). Raw whole-body scans of 641 adults (395 men and 246 women) were obtained from the anthropometric data base of the Civilian American and European Surface Anthropometry Resource project. Following surface restoration of the scans (i.e. patching and smoothing), BSA was calculated. A representative subset of the entire sample population involving 12 men and 12 women (G24) was selected for detailed measurements of hand surface area (SAhand) and ratios of surface area to volume (SA/VOL) of various body segments. Regression equations involving wrist circumference and arm length were used to predict SAhand of the remaining population. The overall [mean (SD)] of BSA were 2.03 (0.19) and 1.73 (0.19) m2 for men and women, respectively. Various prediction equations were tested and although most predicted the measured BSA reasonably closely, residual analysis revealed an overprediction with increasing body size in most cases. Separate non-linear regressions for each sex yielded the following best-fit equations (with root mean square errors of about 1.3%): BSA (cm2) = 128.1 x m0.44 x h0.60 for men and BSA = 147.4 x m0.47 x h0.55 for women, where m, body mass, is in kilograms and h, height, is in centimetres. The SA/VOL ratios of the various body segments were higher for the women compared to the men of G24, significantly for the head plus neck (by 7%), torso (19%), upper arms (15%), forearms (20%), hands (18%), and feet (11%). The SA/VOL for both sexes ranged from approximately 12.m-1 for the pelvic region to 104-123.m-1 for the hands, and shape differences were a factor for the torso and lower leg.

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 (Shivpeak) 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 (VO2max) 53.2 (SD 9) ml O2.kg-1.min-1] participated in the present study to measure and predict Shivpeak. The subjects were initially immersed in water at 8 degrees C for up to 70 min. Water temperature was then gradually increased at 0.8 degree C.min-1 to a value of 20 degrees 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 Shivpeak. Prior to warming the water from 8 to 20 degrees C, the oxygen consumption was 15.1 (SD 5.5) ml.kg-1.min-1 at core temperatures of approximately 35 degrees C. After the water temperature had risen to 20 degrees C, the observed Shivpeak 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) degrees C, respectively. The Shivpeak corresponded to 4.9 (SD 0.8) times the resting metabolism and 41.7 (SD 5.1)% of VO2max. The best fit equation predicting Shivpeak was Shivpeak (ml O2.kg-1.min-1) = 30.5 + 0.348 x VO2max (ml O2.kg-1.min-1) - 0.909 x body mass index (kg.m-2) - 0.233 x age (years); (P = 0.0001; r2 = 0.872).

The purpose of this study was to determine how chronic exertional fatigue and sleep deprivation coupled with negative energy balance affect thermoregulation during cold exposure. Eight men wearing only shorts and socks sat quietly during 4-h cold air exposure (10 degreesC) immediately after (<2 h, A) they completed 61 days of strenuous military training (energy expenditure approximately 4,150 kcal/day, energy intake approximately 3,300 kcal/day, sleep approximately 4 h/day) and again after short (48 h, SR) and long (109 days, LR) recovery. Body weight decreased 7.4 kg from before training to A, then increased 6.4 kg by SR, with an additional 6.4 kg increase by LR. Body fat averaged 12% during A and SR and increased to 21% during LR. Rectal temperature (Tre) was lower before and during cold air exposure for A than for SR and LR. Tre declined during cold exposure in A and SR but not LR. Mean weighted skin temperature (Tsk) during cold exposure was higher in A and SR than in LR. Metabolic rate increased during all cold exposures, but it was lower during A and LR than SR. The mean body temperature (0.67 Tre + 0.33 Tsk) threshold for increasing metabolism was lower during A than SR and LR. Thus chronic exertional fatigue and sleep loss, combined with underfeeding, reduced tissue insulation and blunted metabolic heat production, which compromised maintenance of body temperature. A short period of rest, sleep, and refeeding restored the thermogenic response to cold, but thermal balance in the cold remained compromised until after several weeks of recovery when tissue insulation had been restored.