Anything in life can turn to be either light or darkness.
Many times people with cancer take vitamins and minerals as supplements to strengthen the healthy cells in the body so that they will be powerful, to fight the cancerous cells.
Sometimes the supplements empower the healthy cells and the cancer is defeated, but sometimes the supplements feed the cancer cells and strengthen them.
The same principle works for yoga practice.
Powerful prana (energy) can either decrease ignorance or increase it. It on depends on how we use and direct the energy.
The aim of Hatha yoga (the physical aspect of yoga) is to create a powerful, strong and flexible body which will be capable of containing powerful prana (energy). This powerful energy (also known as Kundalini shakti), pierces the deluded mind and unfolds enlightenment within the practitioner.
However, many times instead of eradicating ignorance, the powerful energy boosts the ego of the practitioner who becomes impressed by the results of their physical practice. The aim of the practice becomes simply manipulating the body into often impossible postures for entertainment purposes. A competitive nature emerges amongst the yogis.
Clinging to the performance of the body will make us attached to our small self, the self that manifests itself through the body and the ego.
Even the most fascinating body will turn back into dust. Clinging to its performance will simply remove us from the path of realization, increasing the attachment to the most temporary part of ourselves, the physical body: the muscles, joints and ligaments.
Prana Yoga College