Neuromuscular factors that impact female athletes’ risk of injury.
Parts 1 and 2 have expanded on the impact anatomical and hormonal factors have on the young female netball athlete. Part 3 focuses on the neuromuscular factors pertaining to female athletes and their risk of injury.
Neuromuscular factors refer to the functioning of the nerves and muscles within the human body, and how they work together to control movement. Poor neuromuscular control and lower limb biomechanics is the main reason for ACL injury in female athletes.
There are four important areas of interest related to neuromuscular factors predisposing young female netball players to injury. These areas of interest include knee valgus motion, knee flexion angle, co-activation of the hamstring and quadriceps muscle, hip kinematics and muscle strength.
Knee Valgus Motion
Knee valgus motion is commonly referred to as knocked knees (the movement of the knees towards each other). Female athletes show higher valgus knee angles compared to males in jumping, landing, side-stepping, hopping, and running tasks.
This poses a serious implication for a knee injury. Valgus knee motion is the primary predictor of ACL injury risk. Almost all ACL injuries occur landing with valgus knee motion which places a large strain on the ACL, predisposing it to injury.
Not only that, but due to the large forces valgus motion places on the knee, we also see a higher rate of patellofemoral pain and patellofemoral pain syndrome in female athletes who show high valgus torques.
Knee Flexion Angle
The angle of knee flexion (knee bending) in female athletes differs from male athletes, as females tend to land with less knee bend.
Having decreased knee bend on landing can increase anterior shear forces (force on the kneecap) and thus a greater load on the ACL, increasing injury risk.
Young female athletes place a higher reliance on their ankle musculature apposed to hip musculature to absorb forces upon landing, requiring them to have their knees in a more straightened position during landing. Majority of athletes who sustain an ACL injury are reported having close to completely straightened knees at the point of injury.
Landing with a straightened knee results in higher forces applied to the knee joint due to the muscles being in an unfavorable position to safely absorb landing forces. These increased forces are transferred directly to the joints and ligaments of the lower limb, in particular, the ACL, heightening the risk of injury.
Furthermore, landing with an extended knee also influences valgus knee motion.
Co-activation of the Hamstring and Quadriceps Muscle Groups
The muscles around the knee joint – quadriceps and hamstring – help to stabilize movements by decreasing large external loads applied to the joint that can increase injury potential.
The co-activation of these two muscles protects the knee against valgus knee motion.
As you land your hamstring muscles should activate before your quadriceps to balance the forward motion of the shinbone (tibia) relative to the thighbone (femur), in order to protect the ACL. If the hamstrings are weak, their co-contraction with the quadriceps will be reduced and cause knee valgus motion and thus loading on the ACL.
Females generally land with greater quadriceps activation and reduced hamstring activation compared to males. During movements involved in netball such as running, side cutting, and crosscutting this is particularly evident.
The imbalance in the activation of the quadriceps and hamstring muscles develops following puberty, prior to this there is no difference between males and females in muscle activation patterns during landing.
During maturation knee straightening strength increases yet knee-bending strength is maintained or weakens. This change creates imbalances between the hamstrings and quadriceps creating an ideal environment for injury.
Hip Kinematics and Muscle Strength
Hip kinematics refers to hip movement biomechanics. Poor hip mechanics have been shown in the research to influence valgus knee motion in landing.
Excessive hip adduction (moving the thigh towards the body) and internal rotation of the upper leg at the hip contribute to valgus knee. Whilst the hip abductors (muscles that move the thigh away from the body) and external rotators work to prevent hip adduction and internal rotation from occurring and protecting against valgus knee.
Studies have shown that female athletes land with decreased hip muscle activity and increased quadriceps activity in single and double leg landing movements, both common in netball. Meaning, the hip is likely to roll into adduction and internal rotation and subsequently, valgus knee motion.
This three-part series as discussed the factors influencing the 10 times higher injury risk female athletes experience compared to males. The Anatomical and hormonal factors we cannot modify (although it is important to be aware of them). However, through proper strength training, we can modify these neuromuscular factors and significantly decrease ACL injury risk in female athletes!
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