The Effect of Inspiratory Resistance on Exercise Performance in Moderate Normobaric hypoxia

Abstract

Various respirators are used to protect workers against toxic airborne substances and pathogens. However, the use of respirators increases inspiratory resistance known to adversely affect physiological and psychological performance in some workers. PURPOSE: To evaluate the effect of inspiratory resistances on physical performance and subjective comfort during exercise in normobaric hypoxia. METHODS: Nine healthy men (Age: 25±2 years, Height: 181.4±6.1, Weight: 92.5±2.6 kg) participated in this study. Subjects breathed through a respiratory mask outfitted with one of four different inspiratory resistors (R) (0, 1.5, 4.5, 7.5 cm H2O·L-1·sec-1) while exercising in normobaric hypoxia (17% O2) for 10 minutes each at 50, 100, and 150 Watts followed by incremental exercise to maximal exertion (VO2max). RESULTS: At exhaustion, added inspiratory resistance in hypoxia significantly decreased the maximal power output (0R=272.2±44.1, 1.5R=263.9±41.7, 4.5R=255.6±34.9, and 7.5R=241.7±50.0 W, respectively, p=0.009), respiration rate (0R=41.9±6.5, 1.5R=39.6±7.6, 4.5R=37.2±6.2, and 7.5R=35.8±6.7 bpm, respectively, p≤0.009), and minute ventilation (0R=106.7±18.5, 1.5R=98.4±13.2, 4.5R=93.2±13.2, and 7.5R=86.7±12.2 L/min, respectively, p=0.002) while oxygen consumption (0R=31.8±4.1, 1.5R=31.7±3.4, 4.5R=30.4±3.4, and 7.5R=31.4±6.4 ml/kg/min, respectively, p=0.750) and heart rate (0R=174.3±10.9, 1.5R=173.9±11.9, 4.5R=177.4±10.1, and 7.5R=171.9±14.3 bpm, respectively, p=0.265) were not significantly changed. Breathing comfort (0R=3.0±1.8, 1.5R=2.7±1.3, 4.5R=4.2±1.9, and 7.5R=4.1±2.0, respectively, p=0.014) and breathing effort (0R=3.7±1.6, 1.5R=3.9±1.5, 4.5R=5.4±1.2, and 7.5R=5.1±1.4, respectively, p=0.001) were significantly increased with additional inspiratory resistance, but rating of perceived exertion (RPE) was not significantly increased (0R=17.8±1.7, 1.5R=18.1±1.6, 4.5R=18.2±0.8, and 7.5R=18.1±1.6, respectively, p=0.664). CONCLUSIONS: Low-to-moderate inspiratory resistance in normobaric hypoxia did not have a detrimental effect on oxygen consumption and RPE at maximal work rates. However, added inspiratory resistance significantly decreased maximal power output and increased perception of breathing discomfort and breathing effort.