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Cold stress severity is routinely described in terms of core temperature (Tc) and heat loss, both of which are dependent upon vascular response, subcutaneous fat, body surface area, muscular composition, and metabolic rate. When exposed to cold stress, variations in each of these can contribute to large differences in heat loss among individuals, wherein some are able to preserve Tc while others are not. The impact of such Tc variations on psychomotor performance is poorly understood. Identifying underlying mechanisms that contribute to impaired performance is important so that strategies can be developed to counteract psychomotor impairments caused by cold stress. PURPOSE: Determine the influence of Tc on psychomotor performance during cold water immersion. METHODS: Thirty-six military personnel (mean ± SD; age: 26 ± 4 yr, ht: 175 ± 8 cm, wt: 79.1 ± 11.1 kg) completed a 10-min whole-body cold water immersion (1°C). Participants' simple reaction time (SRT) was evaluated using a psychomotor vigilance task administered prior to, during, and immediately after immersion, and at three time points (0, 15, 60 min) during a 60-min rewarming activity (entering sleeping bags with dry clothing). For analysis, participants were divided into groups based on their lowest recorded Tc (which occurred immediately after immersion or early in rewarming). Groups were classified as < 35°C (n = 7), between 35-36°C (n = 12), and > 36°C (n = 17). SRT, as well as mean skin temperature (Tsk), hand temperature (Thand), thermal sensation (TS), and shivering sensation (SS), were then compared between groups. Significance was set at p < 0.05. RESULTS: Cold water immersion increased response times for SRT (mean ± SE; pre: 235 ± 12, immersion: 315 ± 14, post: 366 ± 30 ms; p < 0.001). However, no differences were observed between Tc groups for SRT (mean ± SE; < 35°C: 298 ± 31, 35-36°C: 313 ± 18, > 36°C: 326 ± 15 ms; p = 0.677). Additionally, no differences were observed between groups for Tsk (p = 0.409), Thand (p = 0.843), or SS (p = 0.663). CONCLUSIONS: Current findings suggest that psychomotor performance is not greatly influenced by Tc, even in the presence of mild hypothermia. Future work should evaluate other possible contributing physiological factors that impact performance, which will improve understanding of psychomotor performance during cold stress. [ABSTRACT FROM AUTHOR]

The introduction of the Physical Fitness Assessment (PFA) in 1981 provided the U.S. Navy with a tool to evaluate a sailor's overall health and fitness. The PFA is composed of a body composition assessment (BCA) and a Physical Readiness Test. A circumference measurement (CIRC) technique was selected for the BCA to ensure minimal logistics, cost, equipment, and training for fleetwide implementation. In 1984, the Naval Heath Research Center developed gender-specific CIRC equations based on male and female sailor anthropometry and cross-validated them using percent body fat (%BF) from hydrostatic weighing as the gold standard. Accuracy of these equations was supported by a correlation coefficient r = 0.90 and standard error of measurement (SEM) of 2.7 %BF units for men, and r = 0.85 correlation and SEM of 3.7% BF for women. Currently, dual-energy X-ray absorptiometry (DXA) is more commonly used as a criterion for BCA. PURPOSE: To determine the accuracy of the Navy's BCA using circumference measurements to estimate %BF by comparing it with the current criterion using DXA. METHODS: One hundred two (n = 102) active duty sailors (51 male, 51 female) had CIRC %BF measured and then completed a DXA %BF scan. CIRC was measured at the neck and abdomen II (level of the umbilicus) for men, and the neck, abdomen I (minimal waist indentation), and hip sites for women. Height, weight, and age were also obtained from all participants. Pearson product-moment correlation was used to determine the strength of association between CIRC and DXA. RESULTS: Mean ± SD %BF for CIRC versus DXA was 21.9 ± 0.6 and 21.6 ± 0.7%, respectively, for men, and 36.1 ± 1.1 and 32.6 ± 1.0%, respectively, for women. A strong association was found between CIRC and DXA, r = 0.80 (SEM = 2.1 %BF) for men and r = 0.91 (SEM = 2.3 %BF) for women. These values are within the range established when the Navy equation was developed comparing circumferences and hydrostatic weighing. CONCLUSIONS: Correlation and SEM values obtained between CIRC and DXA for both male and female sailors were comparable to similar analyses with hydrostatic weighing. These results indicate that when DXA is used as the criterion, the current Navy circumference equations used to estimate body fat percentage are still accurate. [ABSTRACT FROM AUTHOR]