Despite the explosion of research on ACL injury during the last 30-years, the exact mechanism of injury is still not fully understood. However, a combination of internal (e.g. anatomic, hormonal, neuromuscular) and external factors (e.g. environment, footwear, ground, opposing players) may adequately explain the mechanism [8, 11].
The greatest strain on the ACL occurs during 3-dimensional knee loading, which includes a knee extension moment, proximal anterior tibial shear force, knee valgus/varus moment, as well as a rotational contribution . After ACL reconstruction, altered movement mechanics in jump-landing tasks are often apparent  and have shown to increase the risk of re-injury by 5-15 fold .
Focussing on particular movements that have been associated to ACL injury during landing tasks , such as valgus rotation at the knee joint, movements screens such as the LESS have been developed to identify athletes who may be at risk of sustaining an ACL injury .