EFFECTS OF RESPIRATORY MUSCLE LOADING AND UNLOADING ON TIME TO EXHAUSTION DURING CYCLE ERGOMETRY

Abstract

1077 During maximal exercise with respiratory muscle unloading (RMU), leg blood flow and leg VO2 are increased (Harms et al. JAP 82(5), 1997), while pulmonary VO2 and cardiac output are reduced. In addition, although respiratory muscle loading (RML) had no effect on pulmonary VO2 or cardiac output, leg vascular resistance increased while leg blood flow and leg VO2 decreased. We sought to determine if these cardiovascular and blood flow distribution changes seen at max exercise were associated with performance. Six competitive male cyclists (VO2 max: 65±4 ml/kg/min) each completed 11 randomized trials on a cycle ergometer at 90% of their VO2 max workload. In each trial, respiratory muscle work was either decreased using a proportional assist ventilator (RMU), increased by adding an inspiratory load (RML), or unchanged (control). Time to exhaustion increased significantly (P<0.05) with RMU and decreased significantly with RML compared to control trials (mean time to exhaustion was-10% longer and -20% shorter with RMU and RML, respectively). Perceived exertion and dyspnea ratings were taken throughout each trial. Ratings during the first half of all trials were negatively correlated with time to exhaustion. We conclude that reducing the work of the respiratory muscles improves performance, possibly as a result of blood redistribution from respiratory to working leg muscles.