Ardha Matsyendrasana is a yoga pose that is mainly done to increase the capacity for the lungs. This helps you to take in air and store more oxygen in the body. This is a sitting spinal half twist kind of yoga pose and aids in toning the muscles in the abdomen and the thigh region.

Meaning :

Matsya means fish and Ardha means half in Sanskrit. So Ardha Matsyendrasana means the half twist fish pose.
This yoga pose is best done in early mornings as it relaxes the muscles and nerves for the entire day. It is done on an empty stomach and provides you the right atmosphere for burning calories.

Technique :

First sit with your legs stretched in front of you.
Then bring the feet together and keep your spine straight.
Now take your left leg and bend it and keep the heel of the left foot next to your right hip.
Take the right leg over the left knee and then keep your hand on the right knee and take the right hand behind you.
Now turn at the waist and at the neck and the shoulders and look over the right shoulder.
Now slowly come back to starting position.
Breathe out and release the right hand.
Now release the waist and then ease the chest.
The neck comes last and then you can sit up straight.
Relax.
Now you have to repeat the entire process on the other side.
Care and Caution :

Performing an asana involves a lot of caution. This asana rules the back so if you have a back problem do not do this asana.
Since the Ardh Matsyendrasana aids in relaxing the thigh muscles, it is a good preamble for sex. Thus, it is categorized well under the exercise for sex yoga poses.