The effects of exercise on bubble formation and bends susceptibility at 9,100 m (30,000 ft; 4.3 psia)

This study assessed the value of controlled exercise in a bends susceptibility test. Healthy male subjects were exposed to a pressure altitude of 9,100 m (30,000 ft; 4.3 psia) for a period not exceeding 8 h on two separate days at least 1 week apart. During one exposure, subjects performed five deep knee bends followed by five upward arm extensions with 5-lb weights every 15 min; during the other exposure, they remained sedentary. Exercise and no-exercise altitude exposures were randomized between subjects. A precordial Doppler monitoring technique was used to record venous bubbling at 15-min intervals. Bends was diagnosed from subjective symptoms. Results have shown that controlled exercise decreases time to maximum venous bubbling and increases the incidence of Grade 2 bends compared to no-exercise conditions. Exercise also appears to increase the validity of precordial Doppler monitoring as a method to predict bends onset.