Physiological responses to resistance breathing during short and prolonged exercise

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Abstract
Respirators which impose a resistance to breathing may cause a limitation im maximum exercise intensity. This limitation is of particular concern when respirators are used in emergency situations requiring high levels of exercise intensity. Many studies have defined the limitations of exercise intensity imposed by breathing resistance as the point where the subject fells “uncomfortable.” Perhaps of greater importance is the true physiological limit. Using motivated subjects, the physiological limits of exercise intensity and related respiratory responses were measured for short and prolonged exercise using five breathing resistances. For symmetrical breathing resistances of 11, 16, 25, 40, and 57 cm H2O pressure at a flow rate of 120 L·min−1 exercise limits were 72, 72, 79, 60, and 54 percent of maximum aerobic capacity (% [Vdot]o2 max) for the short term and 58, 60, 49, 43, and 35% [Vdot]o2 max for the prolonged exercise (1 hour). The presence of significant external resistance to breathing was found to influence the traditional relationship between exercise intensity and duration.

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