Breathing in is a an active action requiring muscle. Expiration is passive, so occurs more slowly.
Breathing in - inhalation - takes less time than exhalation.
Normal I:E [Inspiration:Experation] ratio at rest and while asleep is 1:2 or less. On exertion the I:E ratio is 1:1. Inspiration is normally an active process (requiring work). Expiration is passive, and usually longer than the time required for exhalation, resulting an a no-flow period. When breathing spontaneously, the work of breathing is minimised by keeping inspiratory times short and tidal volumes low - just enough to get rid of the produced CO2. To minimise collapse, sighs are taken from time to time.
Inhalation involves (unconscious) respiratory muscle use, most commonly the diaphragm, but also the chest wall muscles and even neck muscles. As I said, it's all done unconsciously, and it's done about 28,000 times a day. these muscles are doing this constantly and are well toned to do it.
The work of breathing is done by the diaphragm, the muscles between the ribs (intercostal muscles), the muscles in the neck, and the abdominal muscles. ... The process of breathing out (called exhalation or expiration) is usually passive when a person is not exercising.
Exhalation under normal conditions is passive. It requires no effort from muscles; in fact, it's the opposite: the muscles relax, and you exhale as they do.
The process of breathing out (called exhalation or expiration) is usually passive when a person is not exercising. The elasticity of the lungs and chest wall, which are actively stretched during inhalation, causes them to return to their resting shape and to expel air out of the lungs when inspiratory muscles are relaxed. Therefore, when a person is at rest, no effort is needed to breathe out.
When exercising, in order to speed O2 delivery to muscles that need it, you must actively assist exhalation. When you need to decrease the expiratory phase duration, you need to actively use muscles not normally used to exhale.
During vigorous exercise, however, a number of muscles participate in exhalation. The abdominal muscles are the most important of these. Abdominal muscles contract, raise abdominal pressure, and push a relaxed diaphragm against the lungs, causing air to be pushed out.
That's not "normal" in relaxed exhalation, therefore the use of these muscles to exhale more actively is noticable.
VENTILATION, VENTILATORS and HUMIDFICATION
Control of Breathing