Purvottanasana is also known as the Upward Plank. This asana stretches the front of the body and strengthens the back of the body. To get into the pose, sit in Dandasana. Hands are hyper-extended as they are placed 1 foot length behind the hips, fingers pointing forward. The elbows are slightly pronated. There is a slight inward rotation of the hip joints as the big toes are placed inwards and heels outward. The adductor magnus and gracilis are in concentric contraction. The uddiyana bandha is engaged.
The hands and inner feet press down firmly on the mat to push up. In this action, the posterior deltoid muscles are in concentric contraction while the anterior deltoid muscles are in eccentric contraction. In addition, the triceps brachii are in concentric contraction while the biceps brachii are are in eccentric contraction. Also, the erector spinae is in concentric contraction while the abdominal muscles are in eccentric contraction. This gives the spine a slight backbend while lifting the sternum up toward the ceiling. At the same time, the rhomboid muscles are in concentric contraction as they draw the shoulders towards the spine. This causes the shoulders to be retracted to open up the chest. This action results in the eccentric contraction of the pectoral muscles. The head drops back as the cervical spine is hyper-extended. This helps to further open the chest.
The gluteus muscles and the hamstrings (bicep femoris and semitendinosus) are in concentric contraction to extend the hips upwards. A strong engagement in these two muscle groups will provide an extra lift to the abdominal organs towards the ceiling, thus stretching them. On the other hand, the iliopsoas and rectus femoris are in eccentric contraction. At the hip joints, the body hinges upwards. Collectively, these actions give rise to an energy rising from the Mula Bandha. The anterior tibialis and gastrocnemius are in concentric contraction as the toes are in plantar flexion.