Reduction of isometric muscle endurance after wearing impermeable gas protective clothing.

The isometric endurance of forearm muscles at 40% maximum voluntary contraction was measured in six healthy male subjects, after they had walked for 25-30 min on a treadmill while wearing an impermeable gas protective suit and a self-contained breathing apparatus at a light (21% VO2 max), and a moderate 41% VO2 max) work level. The mean endurance times were 12% (NS) and 24% (P less than 0.01) shorter than the average control value after exercise for the light and moderate work levels, respectively. These changes were accompanied by an increased heart rate, and rectal and skin temperatures. Ventilating the suit with an air flow of 181 . min-1 at the moderate work level did not significantly affect isometric endurance (decreased 27%), heart rate or body temperatures. It was concluded, that muscular performance capacity is reduced after wearing gas-protective clothing in a temperate environment, presumably due to the increased muscle temperature, and this should be considered in scheduling work times and rest periods.