Purpose: The purpose of this study was to compare cruciate ligament forces between the forward lunge with a short step (forward lunge short) and the forward lunge with a long step (forward lunge long). Methods: Eighteen subjects used their 12-repetition maximum weight while performing the forward lunge short and long with and without a stride. EMG, force, and kinematic variables were input into a biomechanical model using optimization, and cruciate ligament forces were calculated as a function of knee angle. A two-factor repeated-measure ANOVA was used with a Bonferroni adjustment (P<0.0025) to assess differences in cruciate forces between lunging techniques. Results: Mean posterior cruciate ligament (PCL) forces (69-765 N range) were significantly greater (P<0.001) in the forward lunge long compared with the forward lunge short between 0° and 80° knee flexion angles. Mean PCL forces (86-691 N range) were significantly greater (P<0.001) without a stride compared with those with a stride between 0° and 20° knee flexion angles. Mean anterior cruciate ligament (ACL) forces were generated (0-50 N range between 0° and 10° knee flexion angles) only in the forward lunge short with stride. Conclusions: All lunge variations appear appropriate and safe during ACL rehabilitation because of minimal ACL loading. ACL loading occurred only in the forward lunge short with stride. Clinicians should be cautious in prescribing forward lunge exercises during early phases of PCL rehabilitation, especially at higher knee flexion angles and during the forward lunge long, which generated the highest PCL forces. Understanding how varying lunging techniques affect cruciate ligament loading may help clinicians prescribe lunging exercises in a safe manner during ACL and PCL rehabilitation. © 2010 by the American College of Sports Medicine.