Some practitioners contend that muscle-testing can also help diagnose allergies and other adverse reactions to foods. Some have found no difference in muscle response from one substance to another, while others have found no difference between the results with test substances and with placebos. Yet another study showed that suggestion can influence the outcome of muscle-testing. Five out of nine did so. Some people who undergo AK muscle-testing report that although they resisted as hard as they could, the practitioner was still able to pull down their arm.
Distraction can also play a role.
But trickery may also be a factor. I have found that when this is done quickly, the person being tested is unlikely to detect the upward motion. Some practitioners claim that when AK is done properly, muscle-test findings are combined with other information rather than used as a sole basis for diagnosis. But my personal observation of Dr. Goodheart in action, my reading of AK textbooks, and reports I have received from victims suggest otherwise.