Intra- and inter-individual variability of strain during uncompensable heat stress determined from a longitudinal study

Abstract

Four mine rescue brigadesmen performed three different standardized trainings in uncompensable heat stress with different equipment, clothing and climatic stress. The strain during these trainings may be considered as typical for training and missions of firemen, mine rescue brigadesmen and subjects working under protective clothing. - During ten years the diverse trainings were repeated. Heart rates and body temperatures were recorded throughout the exposures. A significant linear trend over time only was found for body mass (increase in three of the subjects). Specific physical fitness (fitness per body mass) as well as heart rate or body temperature showed no significant trend over time for initial or final values. The variability of the physiological strain is described in good approximation by normal distributions and shows quite a high magnitude. On base of the whole data set inter-individual components of variance are estimated by a 2-factorial ANOVA (person, time of measurement) with the factor time of measurement nested under the factor person. Confidence intervals for the estimated mean values and respectively, the calculation of the required number of measurements for a given confidence interval are determined by performing a two factorial ANOVA with both factors fully crossed.