Significance: Landing from a drop has been identified as a movement stressful to the anterior cruciate ligament (ACL). The NCAA has reported that female athletes are six times more likely to suffer a “non-contact” ACL injury compared with males. Muscle activation patterns during the performance of various landing activities have been studied, with males demonstrating greater stabilizing co-contraction about the knee during ballistic maneuvers. Few consistent or significant differences supporting a predisposition of women to ACL injury however have been found with regard to muscle activation. The purpose of this study was to determine if females demonstrate ACL-compromising muscle activation patterns during drop landings onto the heels. Design: Vertical ground reaction forces (VGRF) and normalized EMG data of seven lower extremity muscles were measured as four female and four male subjects performed 2-footed heel landings onto a force plate from a 0.20 meter nominal drop height. All comparisons were tested utilizing a repeated measures ANOVA (P<0.05). Results: Males exhibited greater body weight normalized VGRF peaks (6.4+/-1.4 BW) compared with females (5.9+/-1.2 BW), while females demonstrated slightly more rapid rates of loading (P=0.08). Preparatory, descent and recovery phase durations were not statistically different between the genders. Males demonstrated earlier activation onset times of all muscles compared with females. Mean normalized peak EMG amplitudes were similar between males and females, with females demonstrating greater peak amplitude only in the gluteus maximus (P=0.02). Females exhibited a “bottom-up” order of muscle activation with onset coincident with initial contact. This sequence suggests females were stabilizing the ankle first in preparation for landing, potentially leaving the knee unprotected at the instant of impact when peak anterior shear forces at the knee are generally regarded to occur. Males, conversely, tended to stabilize the more proximal joints first, as demonstrated by earlier and greater co-contractions across the hip, knee and ankle prior to impact. This coincident activation stabilizing the knee and trunk suggests males were attempting to maintain an upright torso in an effort to reduce resultant joint moments at the hip. A large resultant joint moment at the hip may increase the risk for knee injury especially if the heel remains firmly planted and a horizontal acceleration occurs, as during an off-balanced landing. The more proximal muscle activation pattern observed in males has strong training implications for the prevention of ACL injury, as these muscle activation strategies may be minimizing anterior shear at the knee.Keyword(s): athletics/sports, gender issues, safety/injury prevention