Simultaneously with the practice of asanas, there should be effort towards the regulation of the prana. So, asana and pranayama go together. There is an intimate relation between the activity of the physical body and that of the prana. The prana is the total energy which pervades the entire physical system and acts as a medium between the body and mind. The prana is subtler than the body but grosser than the mind. The prana can act but cannot think. The prana is not merely the breath. The breathing process - inhalation, exhalation and retention-does not constitute the prana by itself, but is an indication that the prana is working. We cannot see the prana; it is not any physical object. But we can infer its existence by the processes of respiration. Air is taken in and thrown out by a particular action of the prana. Some hold that there are many pranas and others think it is one. The prana is really a single energy, but appears to be diverse when viewed from the standpoints of its different functions. When we breathe out, the prana operates in one of its functional forms. When we breathe in, the apana functions. The ingoing breath is the effect of the activity of the apana. The centre of the prana is in the heart, that of the apana in the anus. 

There is a third kind of function called samana, the equalising force. Its centre is the navel. It digests food by creating fire in the body and it also equalises the remaining functions in the system. The fourth function of the prana is called udana. Its seat is in the throat. It prompts speech and, on death, separates the system of the prana from the body. The fifth function is called vyana, a force which pervades the whole body and maintains the continuity of the circulation of blood throughout the system. 

This fivefold function of the prana is its principal form. It has also many other functions such as belching, opening and closing of the eyelids, causing hunger, yawning and nourishing the body. When it does these five secondary functions, it goes by the names of naga, kurma, krikara, devadatta and dhananjaya, respectively. The essence of the prana is activity. It is the prana that makes the heart beat, the lungs function and the stomach secrete juices. Hence, neither breathing nor lung-function ceases till death. The prana never goes to sleep, just as the heart never stops beating. The prana is regarded as the watchman of the body. 

The prana is characterized by the property of rajas or restlessness. One cannot make it keep quiet even with effort. The body which is of the nature of tamas is made to move by the rajas of the prana. The prana incites the senses to activity. Because of its rajasic nature, it does not allow either the body or the mind to remain in peace. Such a distractedness is definitely not desirable, and yoga requires stability and fixity in sattva. So, something has to be done with the prana; else, it would become a hindrance to internal tranquillity. The yoga system has evolved a technique by which the prana is made to assist in the practice of yoga, and this is called pranayama. As is the case with asanas, the methods of pranayama in Hatha Yoga are manifold. 

But the yoga of meditation does not require one to practice many forms of pranayama. Just as there is one dhyana-asana, there is one method of pranayama, by which to purify the nadis or nerve-channels and to regulate the prana in yoga. The prana has to be purged of all dross in the form of rajas as well as tamas. 

The prana runs in various channels of the bodily system. It is intensely busy. Its agitated functions disturb the mind and do not allow it to get concentrated on anything. The rajas of the prana also stimulates the senses, and indirectly desire. Any attempt to stop its activity would be tantamount to killing the body. One has to employ a careful means of lessening its activity, of making it move slowly rather than with heaves and jerks. When we run a long distance, climb steps, or get angry, the prana loses its harmony and remains in a stimulated condition. It gets into a state of tension and makes the person restless. So the student of yoga should not engage himself in excessive physical activity causing fatigue. Steady should be the posture of sitting, free from emotions of mind, and slow should be the practice of pranayama. The breathing should be mild, so that it does not produce any sound. One should not sit for pranayama in an unhappy condition of mind, because a grieved mind creates unrhythmic breathing. No pranayama should be practiced when one is hungry or tired or is in a state of emotional disturbance. When everything is calm, then one may start the pranayama. Be seated in the pose of dhyanasana. 

In the beginning stages of pranayama, there should be no retention of the breath, but only deep inhalation and exhalation. The prana has first to be brought to accept the conditions that are going to be imposed on it, and hence any attempt to practice retention should be avoided. In place of the quick breathing that we do daily, a slow breathing should be substituted, and instead of the usually shallow breathing, deep breathing should be practiced, gradually. Vexed minds breathe with an unsymmetrical flow. Submerged worries are likely to disturb pranayama. One may be doing one's functions like office-going, daily, and yet be calm in mind. But another may do nothing and be highly nervous, worried and sunk in sorrow. One should be careful to see that the mind is amenable to the practice. 

In breathing for health, the chest should be forward during inhalation. We feel a joy when we take a long breath with the chest expanded to the full. Deep intakes of fresh air daily are essential for the maintenance of sound health. An open air life for not less than two hours a day should be compulsory. Pranayama is a method not only of harmonizing the breath but also the senses and the mind. Be seated in a well-ventilated room and take in a deep breath. Then, exhale slowly. This practice should continue for sometime, say, a month. Afterwards, the regular pranayama with proportion in respiration may be commenced. The technical kind of breathing which, in yoga, generally goes by the name of pranayama is done in two stages: 

Exhale with a slow and deep breath. Close the right nostril with the right thumb. Inhale slowly through the left nostril. Close the left nostril with the right ring finger and removing the right thumb from the right nostril, exhale very slowly through the right nostril. Then, reverse the process commencing with inhalation through the right nostril. This is the intermediary stage of pranayama without retention of breath and with only alternate inhalation and exhalation. This practice may be continued for another one month. In the third month, the perfected pranayama may be started: Inhale, as before, through the left nostril; retain the breath until you repeat your Ishta Mantra once; and then exhale slowly. The proportion of inhalation, retention and exhalation is supposed to be 1:4:2. If you take one second to inhale, you take 4 seconds to retain, and two seconds to exhale. Generally, the counting of this proportion is done by what is called a matra, which is, roughly, about 3 seconds, or the time taken to chant OM thrice, neither very quickly nor very slowly. You inhale for one matra, retain for four matras, and exhale for two matras. There should be no haste in increasing the time of retention. Whether you are comfortable during retention or not is the test for the duration of retention. There should be no feeling of suffocation in retention. The rule applicable to asana is valid to pranayama, also. Sthira and sukha, easy and comfortable, without strain or pain of any kind, are both asana and pranayama to be in a practice which is a slow and gradual progression of the process. 

The length of time of pranayama depends on individual condition of the body, the type of sadhana one does and the kind of life one leads. All these are important factors which have to be taken into consideration. The normal variety of pranayama in yoga is the one described above, and it is termed 'sukhapuraka' (easy of practice). The other types of pranayama such as the bhastrika, sitali, etc., are only auxiliaries and not essential to the yoga of meditation. There are many details discussed in Hatha Yoga concerning pranayama. One of them, for instance, is that in retention a threefold lock (bandhatraya) consisting of mulabandha, uddiyanabandha and jalandharabandha is preferable. But these are all not directly related to the aim of yoga. Pranayama is not the goal of yoga but only a means to it. Ultimately, it is the mind which has to be subdued and pranayama, etc. are the preparations. When one has to meet a great authority, many hurdles have to be overcome, and many lesser levels have to be satisfied with one's credentials. Likewise, we have these guardians of the bodily system, the pranas, and they cannot be bypassed easily. They have to be given their dues. We have to do something with the body and the pranas, befitting their status and function. We have our social problems and there are also personal problems. Social situations have to be tackled by the practice of the yamas, and the system has to be calmed by the niyamas. The prana is a purely personal affair and its regulation is a precondition to higher discipline. A higher step is not to be attempted unless the lower need is attended to properly. There are no jumps but there is always a gradual progress through every one of the steps, though a step may be comparatively insignificant. By the practice of pranayama, in this manner, is prepared the ground for a rhythm of the body, mind, nerves and senses. The prana actually rings the bell to wake up everything in the system. The powers get roused when the prana is activated. 

The different yoga scriptures detail the methods of pranayama in lesser or greater emphasis. The Hatha-Yoga-Pradipika, the most important text in Hatha Yoga, stresses pranayama more than the practice of asana. What we are physically depends much on how our pranas work. Healthy pranas ensure a healthy body. We are not supposed to take in anything which will irritate the nervous system. The yoga prohibits all extremes in practice. The pranas are to be kept even throughout the year, in all weather conditions and mental states. The texts also enjoin great caution upon the yoga practitioners. 

There was a sannyasin who read books on pranayama, and thought it was all very good. In spite of instructions to the contrary by elders, the Swami went on practicing pranayama, concentrating his mind on the point between the two eye-brows, which should not be resorted to in the beginning stages without an expert guide by one's side. Once, he was at his practice inside his room for three days, and was found missing by others around him. After a search, it was found that his room was bolted from within and he was inside. No shouting by people could wake him and the door had then to be broken open. Even shaking of his body by others could not bring him to consciousness; probably his pranas were locked up in a centre and could not move up or down. His Guru came and keeping his palm on the forehead of the student, he uttered OM, thrice. The practitioner came to his consciousness. People thought he had attained samadhi, but, to everyone's surprise, he was the same old person, with all his negative qualities, and exhibited no signs of one who had tasted samadhi. Later, on his death, his body got so decomposed and melted that it could not be lifted and had to be swept. The student had no spiritual illumination, but only got into a knot through wrong pranayama and spoiled his health in the end. Hence the insistent warning given in all scriptures of yoga. The prana should not be forced to get concentrated in any part of the body. One should not concentrate on any spot of the body above the neck, especially in the initial stages. Concentration on parts in the head directs the prana to that centre, the blood supply gets speeded up to the area and it is then that generally people complain of headache, shooting pains, and the like. No meditative technique should be wholeheartedly resorted to without proper initiation. Also, one should not be under the impression that one can heal others by passing the prana over their bodies. Beginners should not try these methods. One may pray to God for the health or prosperity of any person to whom one wishes good-will, but one should not place one's palm or pass the prana over another in the earlier stages of practice; else one would be a loser. What little one has gained through sadhana might get depleted by such interferences. Out of enthusiasm, one is likely to exhaust one's tapas in these ways. In advanced stages, where one is full with power, there is, of course, no such danger, for one cannot exhaust the ocean by taking any amount of water from it; only if the reservoir is a small well, there is fear of its being emptied. This is the reason why many seekers do not allow people to prostrate themselves before them and touch their feet. This rule does not apply to advanced souls, but Sadhakas should definitely be careful. The gravitational pull of the earth draws the prana down and it tends to pass through the extremities of the body. Brahmacharins and, sometimes, also Sannyasins are often seen putting on wooden sandals, which are non-conductors of electricity, as a protection against this natural occurrence. If someone touches the feet of a student, the prana which he has conserved may pass on to the other, by means of the contact. The prana can be drained off by misdirection and overstrain. Let the pranayama continue slowly, and let no one be quick in the practice. 

The pranayama is not to be done after one's meal. It is better done before food, on empty stomach. No sound should be produced during inhalation and exhalation. In sitting, facing the East or the North is beneficial. There are certain signs which indicate one's success in pranayama. These signs, no doubt, cannot be seen in persons who practice the technique for a short while alone. A lustre in the body, new energy, unusual strength which cannot be easily diminished by fatigue, and absence of heaviness in the body, are some of the indications of progress in pranayama.