It sounds like the therapist was measuring joint position sense. This is called proprioception. The joint is bent or straightened by the therapist and the patient tells when movement is first felt.
Right now researchers are trying to find out more about proprioception. What's normal? Does it change as we get older? Is it the same for men and women? What happens when the joint becomes arthritic? Scientists hope to find an exercise program to restore
proprioception--maybe even reverse the effects of arthritis.