OBJECTIVE The purpose of this study was to evaluate whether knee anterior laxity changes after anterior cruciate ligament injury and surgery are related to aspects of thigh muscle resistance training during rehabilitation. METHODS Forty-nine subjects (13 females) diagnosed with an anterior cruciate ligament-deficient knee or who had undergone anterior cruciate ligament reconstructive surgery participated in this study. The subjects trained their knee extensors in the open kinetic chain during a 6-wk program, and the relationship of aspects of training (for example, absolute resistance load) and other factors to anterior laxity change during this period were analyzed using linear regression analysis. RESULTS The only factor found to be significantly related (r = -0.347) to anterior knee laxity change was average absolute load used in training the knee extensors. CONCLUSIONS These results offer some early clinical support for increasing the strain on the anterior cruciate ligament graft (in patients treated with reconstruction) or other passive restraints to anterior tibial displacement, during rehabilitation after anterior cruciate ligament injury and reconstruction surgery to promote decreased knee anterior laxity.