Following on from our previous blog, we now look to what else can happen when a female athlete lands awkwardly during sports – Quadriceps dominance, leading to locking and hyperextension of the knee!
Part 2. Quadriceps Dominance
Maybe that knee injury you recall wasn’t one where the knee fell inwards and across the body… maybe it locked back into extension as soon as the player’s foot hit the ground? The straight or locked knee version of an ACL injury relates to a neuromuscular imbalance where the knee is primarily stabilised by the quadriceps muscles. Females appear to prefer to use the quadriceps more than males in order to stiffen and stabilise the knee joint. When a female athlete contracts her quadriceps in order to stabilise the knee however, it may excessively straighten (or hyper-extend) her knee, potentially placing it in the vulnerable positions observed during an ACL injury.
When the quadriceps muscles contract, they pull the tibia (lower leg bone) forward relative to the femur (thigh bone). This results in a biomechanical problem, as the ACL serves to hold the tibia from sliding forward, and when a female athlete uses her quadriceps to stabilise the joint, she induces an anterior shear stress to the tibia and therefore also to the ACL. Quadriceps dominance is a result of poor posterior chain activation and strength (is anyone seeing a common theme here…?). If an athlete uses the quadriceps instead of the posterior chain muscles to control the knee, they are using a single muscle for stability and control rather than multiple muscles capable of a lot more strength and support.
One important muscle group of the posterior chain is the hamstrings. The hamstrings are able to increase flexion (bending) at the knee, which provides a better position and mechanical advantage for using the muscles to absorb force. The hamstrings are considered a synergist with the ACL and are able to pull the tibia posteriorly, counter-acting the quadriceps, and thereby decreasing the stress on the ACL.
When looking at your jumping and landing, try to ensure you absorb the force of your landing by bending at the hip, knee and ankle - think squatting. If you need, exaggerate this movement in practice so that you feel comfortable to support yourself without locking at the knees when you are out training and playing– they’ll thank you for it!