8 limbs of the astanga constitute more of a circle

Traditionally the astanga as derived from Patanjali's Yoga Sutras have been described as a ladder.  But different schools of yoga put different emphasis on this map.

Iyengar primarily focus's on asana.  His teaching method says a good foundation in asana practice needs to be mastered before moving into meditation and pranayama.

Maharishi Mahesh Yogi claims that meditation will allow the beginner to experience samadhi.  From that experience of samadhi the other rungs of the astanga will express themselves.

Upon reflection the 8 limbs of the astanga constitute more of a circle than a ladder.

It is possible to mix and match them.  Thus when one practices asana, one still keeps awareness of pranayama(energy,breath); an attitude of pratyahar (detachment); and of course dharana (concentration) on the asana itself.  Underlying everything is the practice of the yamas & niyamas.  A focused approach to asana will unveil samadhi.

The same is true for a pranayama practice.  Requiring pratyahar as an attitude, dharana on the breath, asana to support the practice etc.

Or in (dhyana) meditation, where all 8 limbs come into play in the form of "non-action".  As per MMY.

The artful balance of yoga is in exploring the 8 limbs and how they interact with each other.  Not so much a program of 8 levels, but more a system of 8 actions in which we direct our awareness.

This view of the astanga reconciles the seemingly opposite yogic systems of Iyengar's and Maharishi Mahesh Yogi.