EXHALATION, INHALATION AND RETENTION OF BREATH
Each of us naturally actually performs breath retention (stambha) not even noticing it.
Breathing practices in a yogic way cultivate the natural processes of inhalation, exhalation and breath retention fixing them in the chosen parts of the body and for the chosen period of time. It also transforms our mechanical mind making us conscious beings.
Based on my rich experience with pranayama and its techniques and quite big experience in teaching some of those techniques too I would say that the duration of inhalation, the exhalation and the retention of breath should be chosen personally. This will be especially smart for those who find themselves right at the beginning of this multileveled practice because the quantity and nature of the waves of mind and their expressions differ in every and each person, each and every hour, each and every day.
To those who are right at the beginning of the pranayama techniques it may be a bit difficult to keep the mind concentrated on breathing but as this is just a passing phase one should not give up. The most important for the pranayama techniques is to practice them with complete awareness, big patience and with absolute ahimsa (in this case not injuring own self).
Just in that way one can get his own inner life to know and to transcend it, what ever that in each and everyone’s life may mean.