Great article from Dr. Brian Butler in the U.K.:
A landmark study, titled "On the Reliability and Validity of Manual Muscle Testing: A Literature Review," which presents basic science and clinical research evidence for the reliability and validity of the manual muscle test (MMT) has been published in the Journal of Chiropractic and Osteopathy.
The study, conducted by Drs. George J. Goodheart and Scott C. Cuthbert, included results from more than 100 peer-reviewed studies related to MMT and the applied kinesiology chiropractic technique (AK). It states that good reliability and validity exist for the use of MMT for patients with neuromusculoskeletal dysfunction.
Muscle testing, which is the backbone of applied kinesiology, has been shown to be a reliable and valid method of testing NMS conditions. It now has support for its use in the field of chiropractic to diagnose and treat neuromusculoskeletal dysfunction. Source: Journal of Chiropractic and Osteopathy, chiroandosteo.com