The Series: For details on the Pawanmuktasanas either consult a teacher certified by the Bihar School of Yoga or refer to the book titled Asana Pranayama Mudra Bandha by Swami Satyanand Saraswati himself. The detailed instructions and diagrams are sufficient to get you started on these series that have almost no, or negligible, contraindications.
The Benefits: As prescribed by Swami Satyanand the Pawanmuktasana series must precede other asanas. Holding an asana for a long duration (even if it is only for half a minute) can be quite intense on the muscles involved. The repetitive movements of the Pawanmuktasana series prepare the muscles gently to enable the holding of a posture comfortably and joyously, instead of putting a strain on the muscle and making one prone to injury.
But if one was to do the complete series it can even amount to a full body workout. In fact, the complete series provides a very balanced routine because it engages most of your limbs and muscles. Just because it seems very gentle it may look rather ineffective as far as toning up the body is concerned. But actually, if you practice the complete series just for a month you'll notice considerable physical effects, including toning of the abs.
The ‘simple’ hand, foot and neck movements are anti rheumatic, the ‘simple’ leg movements are great for digestion and strengthening the abdominal muscles and ‘simple’ exercises like chakkichalan and rowing are great for shakti bandhas. And beyond the aforementioned benefits these seemingly simple exercises work at various levels like loosening and stretching of muscles, nerves and joints at the physical level and even at the deeper levels of the energy and the mind.
The Modern Application: Although it can work up to be an effective cardio activity, the simplicity of movements ensures that it works gently even on stiff muscles, hence greatly reducing the chance of injury. I also feel that the Pawanmuktasana series may have been the base for vinyasa yoga, and hence most of the trendy and new age flow yoga styles. In this series the emphasis is on movement and repetition.
My Experience: Even though I have been practicing yoga consistently, whenever I let go of the pawanmuktasanas for a long gap I start seeing the stiffness coming back into the body, especially in my shoulder joints or wrists. I have thus decided to incorporate the Pawanmuktasana series regularly in my practice.