Biomechanical consequences of unbalanced jump landings

This study examined the relationship between unbalanced jump landings and knee biomechanics associated with anterior cruciate ligament (ACL) injury risk under varying levels of cognitive challenge. We hypothesised that unbalanced landing trials would demonstrate riskier early-stance knee biomechanics, particularly under greater cognitive demand. Forty-one physically active adults (17 females, 24 males; 23.7 ± 3.7 years) performed single- and double-leg jump landings from a 30-cm box under three conditions: Baseline (anticipated), Simple (three-choice directional cue), and Complex (five-choice directional cue). Unbalanced trials were defined as those in which participants selected the correct direction but failed to maintain stable balance after landing. Motion capture and force plate data quantified peak knee flexion angle (pKFA), peak knee abduction angle (pKAbA), and peak knee abduction moment (pKAbM) within 100 ms of landing. Mixed-effects models evaluated the effects of Condition, Success, and their interaction. Unbalanced trials demonstrated greater pKAbA than successful trials (p = 0.030), indicating riskier frontal-plane knee mechanics. Simple and Complex conditions produced greater pKFA and pKAbA than Baseline (p < 0.05). No significant Condition × Success interactions were observed. These findings suggest unbalanced landings reveal high-risk knee biomechanics that may be overlooked when only successful trials are analysed and support incorporating cognitive-motor challenges into ACL injury-risk screening and prevention programs.