WORK PERFORMANCE AT 40-DEGREES-C WITH CANADIAN FORCES BIOLOGICAL AND CHEMICAL PROTECTIVE CLOTHING

This study examined the effects of a hot environmental tem perature (40 degrees C and 50% relative humidity) and metabolic rate on soldiers' tolerance time (TT) while wearing various levels of the Canadian Forces biological and chemical (BC) defence protective clothing. The subjects, 19 unacclimatized males, were assigned to exercise at either a light intermittent (LI) (N = 4), light continuous (LC) (N = 5), moderate continuous (MC) (N = 5) or heavy continuous (HC) (N = 5) metabolic rate. For groups LI and LC, exercise involved walking on a treadmill at 4.0 km . h(-1) with a 0% grade and lifting 10 kg boxes. LI alternated between 15 min of exercise and 15 min of rest. Group MC walked at 4.8 . km h(-1) with a 3% grade and lifted 15 kg boxes. Group HC walked at 4.8 km . h(-1) with a 7.5% grade and lifted 20 kg. Subjects were tested wearing three levels of clothing protection: combat clothing (L); combat clothing and a semi-permeable BC overgarment (M); combat clothing and BC overgarment, gloves, boots and respirator (H). TT was the time until rectal temperature reached 39.3 degrees C, heart rate reached 95% maximum, dizziness or nausea precluded further exercise, or 5 h held elapsed. For group LI, TT was similar for L (137 +/- 15 min) and M (117 +/- 9 min) clothing. TT was significantly reduced for H (67 +/- 6 min) clothing. For group LC, TT was greater for L (91 +/- 11 min) compared with either M (68 +/- 7 min) or H (55 +/- 2 min) clothing. For group MC, TT was greater for L (51 +/- 5 min) compared with H (35 +/- 2 min) but TT for both of these levels of protective clothing was not different from M (44 +/- 2 min) clothing. Finally for group HC, TT was significantly reduced from L (43 +/- 6 min) to M (32 +/- 6 min) and to H (25 +/- 3 min) clothing. The decreasing curvilinear relationship between TT and the average metabolic rate was described by a hyperbolic function for each level of BC protection. The vertical asymptote of these functions defined the metabolic rates associated with infinite TT. For each level of BC protection, a resting metabolic rate was above the value associated with infinite TT. These findings implied that even under resting conditions body heat storage and the increase in core temperature would continue. Although intermittent rest periods alone may not reduce the risk of heart casualties, tolerance time will be increased.