So you use the intercostal muscles, the muscles between your ribs, to bring air in and out of your lungs just by expanding and contracting your ribcage, and if I was to put a strap  around the outside of your chest called a breath belt, and just look  at that movement, you see a rather gentle sinusoidal movement, so that's breathing.
para meter ar dentro dos pulmões  e fazê-lo sair, expandindo e contraindo a caixa torácica. Se colocarmos um cinto em volta do tórax, e observarmos esse movimento, veremos um suave movimento sinusoidal conforme respiramos. Estamos sempre a respirar.