Physical therapists coninionly treat lmtients who have sustained complete o r partial tears of the anterior cruciate ligament (A( ;La). O n e goal of rehabilitation is t o cnliance the dvnamic stabilitv of the knee joint without imposing excessive stress on an ACL surgical reconstruction, ;I partially torn ACL, o r secondary restraints that resist anterior tibial tri~nslation (ATT). I'reatrnent programs usuallv emphasire the strengthening of hamstring ~iiuscles to promote dvnaniic support tliat resists anterior tibial shear forces (.5. 7, 14). Clinicians also are concerned with strengthening quadriceps muscles to enhance overall function and knee joint stabilitv.Investigators have examined possible anterior shear forces imposed on the ACI. that result from performing isotonic knee extension exercise ( 1 , 8). Anterior shear forces are defined as the forces that attempt t o affect anterior translation of the tibia relative t o the femur ( 1 1). T h e results of these studies suggest that maximal stress is imposed on the ACL at the end range of knee extension exercise (1, 8). Communications with clinicians and published reports suggest that clinicians have Additional information is needed regarding the effects of exercise protocols on the injured or reconstructed anterior cruciate ligament (ACL). The purpose of this investigation was to assess the effects of knee flexion angle and ACL insufficiency on anterior tibial translation ( A T ) and patellar ligament insertion angle as subjects performed maximal isometric quadriceps muscle contractions. The subjects were two females and two males between the ages of 18 and

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