NONIMPROVER showed a higher asynchronism θ at isotime during PLB than under CB. It is likely that the increased asynchronism between abdomen and rib cage may have jeopardised the possible improvement in exercise tolerance resulting from PLB. There was no significant difference in the degree of asynchronism between PLB and CB in the IMPROVER patients.In COPD patients, the increase in Te promoted by PLB allowed a larger amount of the pulmonary volume to be exhaled, slowing the process of DH that contributes to ventilatory limitation and exercise intolerance. Several strategies that reduce ventilatory demand (physical conditioning and oxygen therapy) and airflow resistance (bronchodilator and heliox therapy) have demonstrated the benefits of reducing DH and increasing exercise tolerance.