The Ashtanga Yoga Primary Series is about moving forward. Moving forward into your best possible self; healthy, flexible in mind and body, and strong.
The muscle groups that primary series targets are the hamstrings, abs, chest & shoulders. The muscle group that most people use as an excuse and hold themselves back from trying a yoga class, tight hamstrings.
The standing sequence and standing asana’s of primary series lengthen the hamstrings, among other things.