Cold and Heat Strain during Cold-Weather Field Training with Nuclear, Biological, and Chemical Protective Clothing

Military Medicine, Feb 2007 by Rissanen, Sirkka, Rintam�ki, Hannu

Results

The VO^sub 2peak^ and peak heart rate (mean � SE) of the subjects were 52.5 � 1.2 mL/kg per minute and 196.6 � 2.5 beats per minute, respectively. During marching, the metabolic rates (mean � SE) on the snowy road and snowy forest were 452 � 7 W (31 � 1% of VO^sub 2peak^) and 576 � 6 W (40 � 1% of VO^sub 2peak^), respectively, estimated from the measured heart rate and the regression analysis of VO^sub 2^ and heart rate on a treadmill. These metabolic rates, based on the energy expenditure, correspond to moderate and heavy activity levels, respectively.22

In Figure 1 is presented an example of Tn, local skin temperatures and T^sub sk^ during marching (including rest at -15�C and transportation by car) at T^sub a^ of -20�C. T^sub re ^was affected by the changes in metabolic rate, rather than in T^sub a^ (Fig. 2), whereas T^sub sk^ was dependent on the T^sub a^. T^sub re^ exceeded 38�C at the heavy activity level.

T^sub a^ values at which thermal and physiological responses met heat or cold strain criteria (discomfort, performance degradation, and tolerance) at different activity levels are summarized in Table I. Finger temperature decreased from a thermoneutral level (28-30�C) to below 15�C (performance) at a T^sub a^ range of -15 to -20�C. Storage of body heat decreased by 6 kJ/kg at T^sub a^ below -15�C during heavy activity and at T^sub a^ below -16�C during moderate activity. PSI values were 2 to 3 and 4 to 6 for moderate and heavy exercises, respectively. CSI values were

Discussion

To maintain physical performance and to prevent possible health disorders, it is important to know the risk limits Involved in the use of NBC protective clothing in cold and warm environmente. Soldiers of the Finnish Defence Forces wear NBC protective clothing against chemical and biological warfare agents and radiation exposures in all weather conditions and in winter. During their training period, the soldiers practice the detection of NBC contaminants in the field and clean chemical spills from used vehicles, for example. The total duration of this field training can be several hours. The activity is mainly light work. Moderate or heavy exercise boute occur when, for example, the soldiers are building roadblocks in snowy terrain or marching.23

Results of the present field study are in accordance with the findings previously made in the laboratory. The increase in T^sub re^ was mainly dependent on the level of physical activity,22 rather than the T^sub a^ during the marches. During heavy work, T^sub re^ could exceed 38�C even at T^sub a^ of -33�C. Wearing a mask may also significantly elevate heart rate and metabolism and concomitantly increase T^sub re^.24 It has been shown that a protective clothing ensemble increases the metabolic cost of walking and stepping tasks, by increasing weight and restricting movements.25 Also, hobbling effects of the clothing7 and increased stiffness of the overall garment attributable to cold11 may increase the metabolic cost and thus heat production.