Papandreou, M. G. ; Papaioannou, N. ; Antonogiannakis S, E. and Zeeris, H. The effect of cross exercise on quadriceps strength in different knee angles after the anterior cruciate ligament reconstruction. Brazilian Journal of Biomotricity. v. 1, n. 4, p. 123-137, 2007. The patients following ACL reconstruction (ACL-R) demonstrate a substantial quadriceps strength weakness which is more pronounced in the early postoperative period. According with the consensus of cross exercise an eccentric training program applied toward resistance exercise on the uninjured knee may be ideally suited to enhance the quadriceps strength on the ACL reconstructed knee. So, the main purpose of this study was to investigate the effect of cross eccentric exercise (CEE) on quadriceps strength at the angles 450 and 900 , in the early rehabilitation phase on the ACL reconstructed knee. Secondary aim was to evaluate the most effective frequency of CCE for enhancement of the quadriceps strength on the ACL-R knee. 42 patients who underwent ACL reconstruction participated in this study. Patients were randomly split into 3 groups, two experimental (E1, E2) and one control. All groups followed the same rehabilitation program. Additionally, the two experimental groups followed 8 weeks of CEE on the uninjured knee; E1-3days/week, and E2-5d/w respectively. The patients were evaluated by isokinetic dynamometer on quadriceps maximal isometric strength at 450 and 900 of the knee flexion, preoperatively and nine weeks post-operatively at both limbs. Two-way ANOVA showed statistical significant differences (p<0.05) on quadriceps strength enhancement at 450 (F=9.11, p<0.01) and 900 (F=46.28, p<0.01) on the ACL reconstructed knee and the above significances observed in the first experimental group compared to the control one. No statistical significant differences were found between the two experimental groups. Adding CEE to ACL traditional rehabilitation program could be beneficial exercise for quadriceps strength enhancement at 450 and 900 of knee motion at a sequence of 3d/w, in the early phase of ACL reconstruction.