Modeling analysis of women litter bearers during heat stress.

BACKGROUND

The majority of military physiological studies have been conducted on men. Consequently most physiological modeling is based on male performance. This study obtained data on women performing military tasks under hot-dry field conditions. Results for rectal temperature (Tre) and heart rate (HR) were compared with values generated by the SCENARIO physiological model.

METHODS

Three skin surface temperatures, Tre, and HR were collected while four female subjects participated in walking or two-person litter carriage (68 kg load) in regular battledress and with full chemical protection at Yuma Proving Ground, AZ. Metabolic rates were measured prior to the test days. Meteorological data were also recorded.

RESULTS

Overall, the potential for thermal stress decreased over the four test days, with air temperature dropping from 39.4 degrees to 35.5 degrees C. Whole body metabolic values were 364 W (walking), 91 W (standing), and 492 W (litter carriage). Endurance times (160 min maximum) for walking were 140 min in Mission Oriented Protective Posture (MOPP)-0 and 29 min in MOPP-4. For litter carriage, the average times were 59 min in MOPP-0 and 43 min in MOPP-4. A comparison of root mean squared deviation (RMSD) to the mean standard deviation for Tre demonstrated a good fit between the model and mean observed values for the MOPP-0 condition. Observed HRs were greater than predicted by the model.

CONCLUSIONS

The modeling results support a conclusion that factors other than heat stress limited litter carriage in MOPP-0. Analysis of calculated values for Tre using RMSD supports an assumption that the male-based SCENARIO may be applicable to females.