Weakness in muscles of breathing is a contributing factor to exercise intolerance and shortness of breath. Thus training these muscles increases respiratory muscle strength and endurance. Breathing exercises like Diaphragmatic breathing, Pursed lip breathing, Buteyko technique, help with controlling episodes of breathlessness & and ultimately improves exercise tolerance.
Source: www.dnaindia.com/lifestyle/report-can-you-manage-your-asthma-with-rehab-know-here-2892362
