Gender and Load Effects on Frontal Plane Kinetics during Single-Leg Drop Landings

Trunk loading during landing alters the lower extremity biomechanical risk factors associated with anterior cruciate ligament (ACL) injury. PURPOSE: To investigate the effects of gender and load on frontal plane kinetics during drop landings. METHODS: Twenty-two (14 F; 8 M) recreational athletes (21±1 yrs) gave voluntary informed consent and performed single-leg drop landings on the dominant leg during unloaded and loaded (5% body mass) conditions. A weight belt distributed the load in three different conditions relative to the dominant leg: ipsilateral (IPSI), contralateral (CON) and symmetrical. A 10 camera Motion Analysis system (500 Hz) and two Kistler force plates (2000 Hz) collected 3D coordinate and ground reaction force (GRF) data. Inverse dynamics methods computed the resultant joint force (RJF) and torque (RJT) at the ankle, knee and hip. Data were normalized using the subject’s weight (GRF and RJF) or the product of their height (ht) and weight (RJT). Mixed design (2x4) ANOVAs determined the effects of gender and load. A Bonferroni adjustment maintained the experiment-wide error rate at p<0.05 for all statistical comparisons. RESULTS: No variable exhibited a gender by load interaction or a main effect for gender. The average normalized mediolateral GRF and the RJFs at the ankle and knee exhibited main effects for load (p<0.05). The CON condition exhibited the largest magnitude forces (GRF = 0.07±0.07 BW; Ankle = -0.49±0.15 BW; Knee = -0.18±0.09 BW) and the IPSI condition the smallest (GRF = 0.04±0.06 BW; Ankle = -0.43±0.16 BW; Knee = -0.15±0.07 BW) (positive forces are medial). The average normalized RJTs at the ankle, knee and hip were in the abduction direction and also exhibited main effects for load (p<0.05). The CON condition had the largest magnitude RJTs (Ankle = 0.05±0.02 BW.ht; Knee = 0.05± 0.03 BW.ht; Hip = 0.11±0.04 BW.ht,) and the IPSI condition the smallest (Ankle = 0.04± 0.02 BW.ht; Knee = 0.04± 0.03 BW.ht; Hip = 0.09±0.03 BW.ht). CONCLUSION: Ipsilateral loading moves the body’s center of mass (CM) toward the landing leg reducing the magnitude of the average medial GRF applied to the foot and resulting in smaller average medial RJFs applied to the distal end of the shank and thigh. In turn, smaller abduction RJTs need to be produced by the muscles of the lower limb to control frontal plane leg motion.