PREPARATORY KRIYÄS FOR PRÄNÄYÄMA

1. Anunásika Breathing  
(Cleansing by inhalation and exhalation)

Sthiti: Any Meditative Posture
Exhale completely. Inhale through both  nostrils and hold the breath for a few seconds.
Blast  out  the  air  through  both   nostrils  in  short  bursts,  until the lungs are completely empty. Repeat  5 times.
Now close the right nostril using the thumb of the right hand. Inhale,  hold  for  a  few  seconds  and  blast  out through left nostril in short bursts of air. Repeat several times.
Next, close the left nostril using the ring and the little fingers of right hand in násika mudrá. Repeat the above process several times through right nostril.
Repeat  the  complete  process  several  times  using  both nostrils. This type of breathing clears the respiratory passages and purifies  the sinuses in the skull.

2. Mukha Dhouti    
(Cleansing through a single blast breath).

Sthiti: Táãásana
PracticE
Spread the legs apart by about 2  feet. 
Lean forward and place the hands on the knees.
Inhale deeply and expel the air forcibly as in a jet through the mouth, continuously. This is effected by contracting the diaphragm as prolonged exhalation. Repeat several times.
 

3. Mukha Bhastriká                               
(Cleansing through hyperventilation)
Kneel down, with the heels together and sit erect.
Inhale fully.
While exhaling  in a series of expulsions of the  breath through the mouth, (keeping the lips puckered as if you are going to whistle)  bend forward and rest the head on the ground in front of the knees. The expulsions are done with the help of the abdominal muscles.
Inhale, come up slowly.
Repeat several times.
The purpose of Mukha Bhastrika is to reduce the level of carbon di-oxide present in the body. Also a cleansing practice.

4. Viparètakaraïi Kriya (cleansing in inverted posture)

Sthiti: Supine Posture

PRACTICE
Raise the legs to 900, keeping the
knees straight.
Raise the buttocks and the trunk off the ground by supporting the body with the hands at  the waist to transfer the weight to the arms and elbows.  Keep the elbows as close to each other as possible.
Slowly move into the final position of Viparita karani by raising  both legs to vertical position and maintaining the trunk at an angle of 450 to the ground.
In the final position the weight of the body rests on the shoulders, neck and the elbows,  the trunk is at 450 angle to the floor, the legs are straight and perpendicular to the floor.  Note that the chin should not press against the chest.
Close the eyes and feel comfortable.
Focus the awareness on the perineum i.e., the area between the anus and the genitals.
Now slowly in a rolling motion, pull the buttocks inwards. 
Then contract the anal sphincter muscles and pull the anus inwards and upwards.
Hold it as long as possible with normal breathing.
Release the bandha and then retrace the steps to come down to the supine sthiti and rest in Ùavásana for a while.

Note
Apart from Mülabandha the following practices can also be done in the final position of Viparitakaranii such as  Deep abdominal breathing or Kapálabháti or Ashvini Mudra.
Mülabandha can also be performed with antarkumbhaka (holding the breath after inhalation).
Practice a few rounds.
Ashvini Mudrá, in fact, is a good preparatory practice for Mûlabandha and  can be practiced in the following way:
     

“Contract the anal sphincter muscles and pull the anus inward and upward.  Hold for 2 to 3 seconds.  Then relax.  Repeat this as many times as you can with normal breathing. Continue  to briefly contract and relax  as rhythmically and evenly as possible.  Once this is mastered, Mülabandha can be performed quite effectively.”   

Benefits
It stimulates and tones the uro-genital and excretory systems. Intestinal peristalsis is also stimulated, relieving constipation and piles. It is also beneficial for anal fissures, enlarged prostate, urgency and frequency of urination of irritable bladder,  early case of prolapse of uterus, etc.

Limitations
Constipation is a side effect of mulabandha or Ashvini mudra.