The pause brought in the movement of inhalation and exhalation is called  Pranayama. There are four types of Pranayama on the basis of the nature of the 'pause' that causes a temporary suspension of breath:

1. Pause after or at the end of a prolonged and very slow exhalation.
2. Pause after or at the end of deep and prolonged inhalation. 
3. Pause is brought any time in between the usual inhalation or    exhalation. This is a prolongation of a break in breathing.
4. Pause is experienced by the practitioner at any time without his voluntary efforts, after a long practice of above three types of pauses.

• When the breath is held after exhalation, it is called Bahya Kumbhaka.

• When the breathing is stopped after inhalation, it is known as Abhyantara Kumbhaka. 

• The fourth type of pause mentioned above is known as Keval Kumbhaka.

The slightest change brought in the normal speed of breathing is Pranayama. So, prolonged inhalations and exhalations done systematically are Pranayama. Obviously, to do this, a voluntary control is necessary. In normal breathing also, there is a pause between inhalation and exhalation which may be for a few mill-seconds only. Therefore, a voluntary control brought on any one of the three i.e. inhalation, exhalation or the pause, or on all the three, will be called Pranayama.
 

• Pranayama essentially consists of a voluntary control on the breathing and probably due to this fact, it is referred to as 'breathing exercise' by many people.
   

• Various breathing exercises have been developed with the purpose of providing more oxygen to the system.
   

• In Pranayama, on the contrary, the emphasis seems to be given on the development of Kumbhaka, i.e. a controlled phase of breath holding.
   

• Pranayama is normally done in a relaxed sitting condition in which the demand for oxygen from the body is minimal.
   

• When the hemoglobin is fully saturated with the oxygen, no further quantities of oxygen can be accepted. Our body cannot and does not store oxygen. 
   

• During Kumbhaka phase, the air gets more time for exchange of gases with the blood. Naturally more carbon-dioxide is accumulated in the lungs than usual.
   

• Calculations clearly show that the amount of oxygen obtained by our body during one minute of Pranayama is lesser than that obtained during one minute of normal breathing. It is, therefore, wrong to say that in Pranayama one gets more oxygen. 
   

• Practice of Pranayama requires a conscious control over the breathing.
   

• One remains fully aware of what he is doing during the different phases of Pranayama. In other words, Pranayama is never done mechanically.
   

• Awareness of breathing is most important while practicing Pranayama.
   

• No other bodily action is associated with Pranayamic phases out side the body. 
    

• Talking and singing are also voluntarily controlled respiratory acts but they cannot be compared with Pranayama. Singing or talking involves some kind of emotions or expressions and moreover, they are the acts of communication. Pranayamic breathing does not produce any emotion, nor does it express any thought or desire. 

Each cycle of Pranayama is a complex voluntary act, consisting of three distinct phases i.e. Puraka, Kumbhaka and Rechaka. Three types of Kumbhakas are possible as follows:

1. Abhyantara or Puma or Antarkumbhaka: This is a controlled suspension of breath after Puraka. Since the inspired air is compressed in the alveoli during this retention, the intra-pulmonic pressure is raised and maintained for some length of time.
 
2. Bahya or Shunya Kumbhaka: This is a controlled retention of breath after Rechaka phase. The intra-pulmonic pressure is lowered
and maintained for some length of time.
 
3. Keval Kumbhaka: The suspension of breath appears automatically somewhere in the mid stage of respiratory acts after considerable practice of Pranayama. This stage is characterised by equal atmospheric and intra-pulmonic pressure.
 

Hatha yoga recommends to apply some bandhas along with each cycle of Pranayama. 

• Moolabandha is practiced during Puraka. 

• Uddiyan bandha is done in Rechaka.

• In Kumbhaka, all the three bandhas; i.e. moola, jalandhara and uddiyan  are advocated.