Something many people seem to not know about hatha yoga is that many (if not most) asanas aid and improve digestion and circulation as a way to improve the flow of prana (life force energy) in the body.
Navasana can be modified in a number of ways but the purpose of it is always to engage the upper abdominal muscles.
As we breathe deeply in this asana, pressure is put on the lower digestive organs (intestines and colon) to stimulate peristalsis. This can be a wonderful asana for those experiencing constipation due to stress, including when we haven’t been eating well because we are stressed out and our digestion has slowed as a result.
It is best to avoid this asana directly after eating – it is best practiced first thing in the morning before you have taken in food for the day, in order to fire up the digestive system. Practicing after meals may result in heartburn, stomach upset, or nausea.
Some possible contraindications / cautions:
Back/neck injury
Pregnancy
Menstruation
Low blood pressure
Headaches
Nausea
Heart problems
Asthma