Expand-A-Lung Respiratory Breathing Fitness Exerciser Trainer Resistance Adjustable Air flow Valve for AthletesProduct description The flow of air in and out of the alveoli is called ventilation and has two stages: inspiration (or inhalation) and expiration (or exhalation). To accomplish this, the whole thorax moves and changes size, due to the action of two sets of muscles: the intercostal muscles and the diaphragm. These are the muscles that are strengthened by using the Expand A Lung Breathing Resistance Exerciser. In essence, you inhale more oxygen, and