Many people have a tendency to shrug their shoulders, hang their heads slightly (smart phone-itis), and/or hunch their backs. That’s one of the reasons why I encourage people to reach up and back as they practice their sun salutations.
In the Sivananda tradition, urdhva hastasana with an arched back, is the second and eleventh of the 12 steps in the sun salutation. In this manner, one is getting the benefits of opening the solar plexus, heart and throat chakras, while applying a bit of pressure to the kidneys and adrenal glands. Plus, the backbend counteracts our daily routines that may lead to poor posture, respiratory and digestive issues.
In the Sivananda tradition, the sun salutations are of primary importance. Same with Ashtanga. My first Sivananda mentor said if I had time for nothing else, do six sun salutations, daily. More recently, my Ayurvedic doctor prescribed 12 sets of sun salutations for me, daily.
Swami Vishnudevananda is credited with bringing Sivananda Yoga to the West. He was a direct disciple of Swami Sivananda, who was a trained medical doctor. “Health is wealth. Peace of mind is happiness. Yoga shows the way,” Vishnudevananda said. And, “Yoga aims to remove the root cause of all diseases, not to treat its symptoms as medical science generally attempts to do.”
As always, when arms are lifted, try to keep the shoulders down to relax the trapezius. Those suffering from shoulder issues should be sure to ask their physical therapist, osteopath or yoga therapist about any movements/postures to avoid.