The purpose of this study was to investigate alterations in lower extremity kinematics during the landing phase of a countermovement jump when performed in different environments and under multiple external loads. Twenty-four NCAA Divison I collegiate female athletes performed 12 countermovement jumps on land and 12 jumps in water, submerged to the xiphoid process, for a total of 24 jumps. Within each environmental condition, four loading conditions of three jumps each were performed using a weighted vest: Unloaded, 10%, 20%, or 30% of body mass. The hip, knee, and ankle angles were measured as the smallest angles between the major body segments (trunk, thigh, shank, and foot) in the sagittal plane using the digital goniometer tool from Kinovea video analysis software at the point of maximum knee flexion. Larger angles indicated decreased joint flexion and smaller angles indicated increased joint flexion. The mean hip, knee, and ankle angles were significantly greater for the jump landings in water compared to on land, regardless of load (133.7° vs. 113.9°, 119.5° vs. 107.5°, and 91.7° vs. 85.6°, p \u3c 0.001). Independent of environment, the loading conditions also affected the joint angles. The unloaded hip angles were significantly greater than the 10%, 20%, and 30% loaded angles (128.0° vs. 123.3°, 122.5°, and 121.6°, p \u3c 0.001) and the unloaded ankle angle was significantly greater than the 10%, 20%, and 30% loaded angles (89.6° vs. 88.5°, 88.4°, and 88.0°, p = 0.015, p = 0.023, and p = 0.007). Increasing lower extremity joint flexion during jump landing may help minimize ACL injury. The decreases in joint flexion during the aquatic jump landings may have occurred due to the off-loading from the buoyancy characteristics of water, which may be less harmful compared to decreased joint flexion on land. The significant increases in joint flexion due to loading condition may provide evidence for use in athlete training programs to help decrease the probability of ACL injury
