Divergence analysis of failed and successful unanticipated single-leg landings reveals the importance of the flight phase and upper body biomechanics

Functional knee brace use for 21 h leads to a longer duration to achieve peak vertical ground reaction forces and the removal of the brace after 17.5 h results in faster loading of the knee joint

“…However, it is well-established that the neuromuscular response time required for muscles to actively protect knee joint ligaments from loading and possibly prevent an ACL injury episode ranges between 60 and 150 msec [47]. Some have suggested that preactivation of knee joint agonist and antagonist muscles (before IGC) may protect against a noncontact ACL injury [22,40]. However, other researchers have shown that preactivation increased knee joint stiffness reduced GRF absorption [34], and led to a higher Q: H ratio, specifically due to decreased hamstring activation, which is negatively correlated with the knee flexion angle at IGC [46], and quadricepdominant activation could affect axial compression forces immediately after IGC, resulting in a reduction in the force required to rupture the ACL [10,22,34].…”

“…To reduce the risk of noncontact ACL injury by up to 40%, researchers have suggested that an increase in trunk/hip and knee flexion with concurrent activation of the hamstring and deactivation of the quadricep muscle groups could lead to the desired result of increased absorption of GRF/decreased ACL loading [30,35]. Furthermore, it has been suggested that before IGC, preactivation of the knee joint agonist and antagonist muscles leads to increased joint stiffness, which can provide greater knee joint stability and protection against a noncontact ACL episode [22,40]. On the contrary, during jump landing, researchers have suggested that increased joint stiffness may reduce GRF absorption [34]; preactivation of the knee joint agonist and antagonist muscles led to a high quadricep: hamstring (Q: H) ratio (mainly due to decreased activation of the hamstrings), which was negatively correlated with the knee flexion angle at IGC [46], which reduces the force threshold required to rupture the ACL [34,41].…”