EXERCISE PERFORMANCE DURING INSPIRATORY RESISTANCE BREATHING UNDER EXHAUSTIVE CONSTANT-LOAD WORK

The purpose of this study was to determine the effects of different in spiratory resistances on exercise performance and to describe physiolo gical and subjective responses during constant load work of an intensi ty that elicits the maximum sensitivity to respiratory factors of resp irator wear. Nine subjects (mean age 25.8 +/- 4.8 years) performed exh austive treadmill exercise during constant load work of 80% of maximal aerobic capacity while inspiring against one of five randomly assigne d inspiratory resistance conditions. For inspiratory resistances of 0. 20 kPa (R1), 0.29 kPa (R2), 0.39 kPa (R3), and 0.49 kPa (R4): measured at a steady air flow rate of 85 L min(-1), average performance times were 84, 75, 54, and 30% of the control condition. Performance time re ductions were significant for R3 and R4 trials. Results also indicated a significantly reduced mean respiration rate, minute ventilation, an d oxygen ventilatory equivalent (V-E/VO2) for the R4 condition at exer cise breakpoint compared to control. For resistances R1 - R4, mean V-E /VO2 were significantly reduced from control by approximately 12, 17, 19, and 31%. At breakpoint, mean ratings of perceived exertion were si milar for control, R1, R2, and R3 conditions but were significantly lo wer for R4 versus control. Breathing comfort did not differ significan tly between resistances below the R3 level, but discomfort was signifi cantly greater for conditions R3 and R4. These findings suggest that t he impact of the respiratory limitations of respirators can be diminis hed by employing respirators with inspiratory resistances below the R3 level.