In the mammalian respiratory system, eupnea is normal, good, unlabored breathing, sometimes known as quiet breathing or resting respiratory rate. In eupnea, expiration employs only the elastic recoil of the lungs. Eupnea is an efficient and effective form of breathing, which maximizes air intake, and minimizes muscular effort. During eupnea, neural output to respiratory muscles is highly regular, with rhythmic bursts of activity during inspiration only to the diaphragm and external intercostal muscles.