Some offer incoming breath (prāna) to outgoing breath (apāna), and the outgoing into the incoming. Restraining the incoming and the outgoing breaths alike, they pursue breath regulation, prāṇāyāma.
Respiration, like blood circulation, is an incessant process. Its speed and intensity vary depending upon the bodily activity. Wrong application of body and mind will reduce longevity. With wish and will you can regulate breathing effectively.
To restrain the breath within is internal kumbhaka. To restrain it outside after exhalation, is external kumbhaka. Both have startling healthy effects on body and mind.
The third regulation is to make entry and exit equal, light, thin and smooth. Breathing can be even soundless. It will render the mind-process light, smooth and gentle. Breath can be effectively used to handle the mind. Praṇayama is very effective to make the body healthy, and the mind strong, stable and harmonious. While rendering no harm, it bestows immense benefit.