Applied kinesiology is alternative therapy/New Age practice which uses muscle testing as a way to evaluate neurological functions. It is said to be useful to correct posture, relax muscles and relieve tension, and improve functioning of weakened systems.

How did applied kinesiology develop?
Applied kinesiology started with a chiropractor named George Goodheart in the 1960's. By combining the concept of "innate intelligence" with the Eastern idea of ch'i and the idea that muscles reflex the condition of each of the various body organs via the ch'i meridians. His theory was that the condition of all of the body's organs and systems could be checked by examining the resistance of a specific muscle in the body. Variations of his theory use the deltoid or finger muscles as the testing muscles. His discoveries were made public in 1964 and since then he has lectured, researched, and written about the effectiveness of applied kinesiology. Several forms of the practice have evolved since the 1960's and include Applied Kinesiology, Behavioral or Bio-Kinesiology, MRT, and Contact Reflex Analysis.

How does applied kinesiology work?
The practice can be divided into two parts: diagnosis and treatment. Diagnosis involves testing the muscles to determine what systems are function abnormally, such as the vascular or nervous system. First, patients are questioned about their health. Then, a general examination is given which includes monitoring blood pressure and then more specific tests on the muscles are performed to uncover the cause of any problems the patient may be having. The treatment phase can involve anything from nutritional changes to acupuncture to chiropractic manipulation. Techniques are borrowed from a number of different disciplines and it is claimed through testing and the knowledge of the practitioner the exact needs of the patient can be determined.

Who practices applied kinesiology?
Applied kinesiology practitioners are heath care professionals ( doctors, nurses, dentists, etc.) who studied the practice in addition to their main field of study. Basic classes include over 100 hours of classroom time and home study and practice. A proficiency exam is required at the end of the basic course and in order to receive a diploma in the field of applied kinesiology over 300 classroom hours are required in addition to multiple papers and practice sessions.

Sources:
http://www.hcrc.org/faqs/appkin.html
http://www.icak.com/FAQ/faqs.html