Mid-flight trunk flexion and extension altered segment and lower extremity joint movements and subsequent landing mechanics

To assess the effect of mid-flight trunk flexion and extension on the movements of body segments and lower extremity joints and subsequent landing mechanics during a jump-landing task. Participants performed three jump-landing conditions in a randomized order. Forty-one participants completed jump-landing trials when performing three different mid-flight trunk motion: reaching forward, reaching up, and reaching backward. Whole-body kinematic and ground reaction force data were collected. The reaching backward condition resulted in a more posteriorly positioned upper body center of mass (COM) and more anteriorly positioned pelvis COM, legs COM, hip, and knee joint positions relative to the whole-body COM in flight and at initial contact of landing. The reaching backward condition showed the least hip flexion and ankle plantarflexion angles at initial contact as well as the least hip and knee flexion angles and the greatest ankle dorsiflexion angles at 100ms after landing. The reaching backward condition also demonstrated the greatest peak posterior ground reaction forces, peak and average knee extension moments, peak and average hip flexion moments, and peak knee varus moments within the first 100ms after landing. Opposite changes were observed for the reaching forward condition. Mid-flight trunk extension resulted in body postures that predisposed individuals to land with increased knee extension and varus moments and decreased knee flexion angles, which are indirectly associated with increased ACL loading. These findings may help to understand altered trunk motion during certain ACL injury events and provide information for developing jump-landing training strategies.