Surya namaskar: Hasta Padasana

The tenth pose in Surya Namaskar is the forward bending pose or the hasta padasana (as in the 3rd pose).
• Posture: From the ninth pose or the ashwa sanchalanasana, bring the right foot forward and next to the left foot, simultaneously as you extend or straighten the left knee, to come into standing position. The hands stay on the floor as they are, on either side, with the feet in between. When the flexibility in the posterior chain of soft tissue (the calf, the hamstrings, gluteii, latissimus dorsii, quadratus lumborum, spinal extensors and thoraco-lumbar fascia) is good, the palms of hands may rest on the floor, with the elbows in extension or even some amount of flexion. When the flexibility in the afore-mentioned soft tissue is not so good, one may need to stretch out fingers to reach the floor or perhaps is unable to reach floor. In this case, it is alright to slide hands along the front of legs as far down as possible. With increased hamstrings flexibility, the pelvis rotates forward as the hip flexes, and with sacral nutation( forward tilting of sacrum) , most flexion should occur at hip joint with the abdomen as close to the thighs as possible. The spine should be elongated. When excessive flexion occurs in the lumbar and upper thoracic spine, with a “kyphotic” T-spine, or overall curved spine(C-shaped), the hip joint is/are(one joint /both joints) not flexing much and abdomen is further from the thighs. This calls for stretching of the posterior chain of soft tissue or increasing hip flexion mobility (close-chain movement with acetabulum rotating over a stable head of femur). In case of less flexibility, one may begin with the knees in some flexion in order for hands to reach the floor, and then reverse the movement by extending the knees to stretch the posterior chain. In the final posture, the knees are straightened. 
• Muscles: As the right foot comes forward, the dorsiflexors initiate this movement with the hamstrings and hip flexors contracting to lift and bend the leg and clear the ground in order to bring the right foot next to the left in one smooth, sweeping motion. Then, the quadriceps takes over to extend the knees bilaterally, to enable standing on both feet. The trunk stabilizers keep the spine stable and erector spinae elongates the spine in synchrony with the trunk stabilizers. The posterior chain as mentioned above stretches to allow uninhibited mobility into forward flexion. Hip flexors including iliopsoas, pectineus, sartorius, and rectus femoris contract to flex hip and rotate pelvis forward. 
• Breathing: In the final position of the ninth or ashwa sanchalanasana, you breathe in and hold. You may begin transitioning into the 10th pose or the hasta padasana or forward bend by breathing out. In the final phase of this pose, complete exhalation is performed which allows deepening of the pose. You may stay in this pose with 2-3 breath (in and out) cycles, deepening the pose and approximating the trunk to thighs each time you exhale.
“Om Savitre namah” 
“I bow to Him who produces everything”