Further- in the realm of Asanas of Hatha Yoga, many modern yogis especially use yoga in a secular style as a form of physical exercise, and it is very useful as such. Taken out of the context of Yoking to a Universal Deity or Foundational Source, it becomes simple a way to maintain vigorous health. The problem is that it tends away from the touchpoints of meditation, Prana, and internal pathways, and becomes stretching. Stretching is good, healthy activity, but it often stops at the muscle , perhaps opening some of the muscle and tendon connection. It can become somewhat shallow in it's effect. I am not knocking it, and I think it is absolutely necessary, but to gain high levels of energy flow requires spending time in the ligaments, fascia and bone. The methods of Internal stretching, Daoyin and Martial QiGong contextualize the energy in a manner not unlike the spiritual path that originated Hatha Yoga- finding a way deeper into the body using the mind, the intention, and ultimately the Spirit to open Chakras, or Dantien, centers of energy which are Important to both Indian and Chinese mystery schools.