It has long been recognized that limb injury produces relative atrophy and weakness, which can cause an increased susceptibility to reinjury. In 1964, Bender et all concluded from a study of the lower body strength of 806 West Point Cadets that &dquo; ... individuals who have strength differences greater than 10% between the limbs, and also those in the lower quartile strengthwise, are more likely to be injured than are those who possess normal strength levels.&dquo; These studies were limited to isometrics, with the subjects tested according to the multiple angle testing method and then exercised with an isometric program. There are few data concerning which muscles are weakened in response to particular injuries, other than the prime movers of joints, for example, the quadriceps when there is a knee injury.There have been many devices used to measure strength and power -but investigators have for the most part studied isometric and isotonic contractions. Martin2 published as far back as 1921 the ergographic, dynamometric, and resistive strength tests and compared the efficiency of these methods. Despite the invention by Mosso of the ergograph in 1884,~ there is still a great difficulty in obtaining uniform data to test muscular efficiency in the knee. With the advent of an isokinetic apparatus such as the Cybex II, we have attempted to extend 3ender's findings isometrically to isokinetic findings. Whereas Bender studied muscle imbalances in and around the site of injury, and described what occurs in muscles which control the leg injury, our study was aimed at defining the existing relationships between an injured part of the extremity and muscle groups far removed anatomically from the site of injury. This is in accordance with what we feel are valid postulates, described by Schmier in 1945. METHODS Patient groupsPatients who were examined at the Lenox Hill Hospital, Institute of Sports Medicine and Athletic Trauma, were classified into a number of categories according to the nature of their musculoskeletal disease or injury. These were defined by orthopedic surgeons after a comprehensive musculoskeletal examination. Most of the patients in these categories continued to have a disability long after their original acute injury was assumed to have healed, and continued to