Biomechanical faults are necessary, but not sufficient to cause ACL injury in isolation. Zoom out and these injuries are products of complex non-linear systems failure. 

Sport is a complex system. The final score is determined by the relative skill and performance of individual players, how each player and coach interact with teammates, the ever-evolving dynamics of the game (e.g., substitutions, crowd noise, refereeing, etc.) and the elimination of time on the game clock. The two interacting teams are rarely “perfect”, but each adapts to faults in order to score points, maximize possessions, and win. This feature of adaptation is true of all complex systems: despite obvious flaws, the complexity allows for variability in the way the systems run. 

In this regard, biomechanical faults are a “minor flaw” of human movement and do not always result in injury. Could natural biomechanical variability be the scapegoat of wider systems failure?

Biomechanics is a key part, but oftentimes isn’t the most meaningful part. The harder-to-measure contextual stuff is driving the system. Stop and consider all the factors influencing how an athlete moves on-field. How might we prepare athletes for these under-appreciated factors?

Clinical tip: Cognitive or motor dual-tasks can be used early in rehabilitation to increase complexity. Titer the difficulty to just disrupt perfect performance, train, then repeat.