In Kundalini Yoga a kriya is a series of postures, breath, and sound that work toward a specific outcome. Practising a kriya initiates a sequence of physical and mental changes that affect the body, mind and spirit simultaneously. There are kriyas that support the liver, balance the glandular system, make you radiant, stimulate the pituitary, increase the flexibility of the spine, and many more. Each kriya has a different effect, but all work on all levels of your being.
Using the angles and triangles of the asanas, fueled by the prana of the breath, re-tuned by the repetition of mantra, and concentrated by eye-focus and body locks, you are physically different by the end of kriya. These changes assist the physical and mental preparation of a meditative internal space. This framework for meditation occurs in numerous ways; opening the joints to facilitate sitting, altering the chemical constituents of the blood via glandular stimulation, and redirecting the mind through concentration and focus.
An important aspect of the power of Kundalini Yoga is that each kriya is whole unto itself, a perfect jewel that acts to create a flow. They are perfectly designed sets of exercices meant to produce predictable and subtle impacts on the total Self.