Part 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 (1 – 5), such as young netballers. 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. A review to expand your understanding of how these factors impact your young female netballers in being prone to injury is as follows.
Knee Valgus Motion
Knee valgus motion is commonly referred to as knocked knees (the movement of the knees towards each other). The measurement of knee valgus angles during landing shows females land with a significantly higher knocked knee motion at ground contact (6). Compared to males, females tend to land with more knee valgus motion. (4, 6-8). In regards to movements related to netball, when jumping and landing, side stepping and completing shuttle runs females land with greater knee valgus across all movements compared to males. Similarly, when landing from forwards, back wards and vertical jumps, which are also involved in the sport of netball knee valgus motion is increased.
Knee valgus is a primary predictor of ACL injury risk, specifically for female athletes. During landing on one or both legs, females show knee valgus movement. Females who sustain an ACL injury will most likely have landed with knee valgus motion, which puts increased strain on the ACL, predisposing the knee to injury.
It is evident that female netballers who land with increased knee valgus motion across all movements predisposes themselves to injury, particularly ACL rupture.
Knee Flexion Angle
The angle of knee flexion (knee bending) in female athletes differs to male athletes, as females tend to land with less knee bend (9). 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 (4).
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 (11). Majority of athletes who sustain an ACL injury are reported having close to completely straightened knees at the point of injury (10).
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 (2).
Young female netballers who land with their legs straight rather than bending at the knee and absorbing forces as the land, increase their risk of injury.
Co-activation of the hamstring and quadriceps muscle groups
The muscles around the knee joint – quadriceps and hamstring – help to stabilise the ligaments by decreasing large external loads applied to the joint that can increase injury potential (11). The co-activation of these two muscles protects the knee against adduction (movement towards the midline) and valgus motion. (11, 1) As you land your hamstring muscles should activate beforehand to balance the forward motion of the shinbone (tibia) relative to the thighbone (femur), in order to protect the ACL (11). 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 (11, 4).
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, as prior to this there is no difference between males and females. During maturation knee straightening strength increases yet knee-bending strength is maintained or weakens. This change is what makes female netball athletes more prone to injury, such as ACL rupture.
Hip Kinematics and Muscle Strength
Hip kinematics refers to hip movement biomechanics and has been shown to cause increased knee valgus motion upon landing in female netball athletes, increasing the forces placed on the ACL and the possibility of sustaining an injury (13-15).
Excessive hip adduction (moving the thigh towards the body) and the internal rotation of the upper leg at the hip contribute to the increased knee valgus. Whilst weight bearing your hip abductors (muscles that move the thigh away from the body) and external rotators activate to prevent hip adduction and internal rotation. From occurring and again reducing knee valgus movement (16).
Female athletes land with decreased gluteus maximus (GM) activation and increased quadriceps activation in single and double leg landing movements, common in netball activity (17). GM is a hip muscle and its activation and strength is connected to knee valgus motion as it works to externally rotate the hip to aid hip abduction and stabilize the knee joint (14).
Hip muscle weakness contributes to poor motion of the lower body. If female netball athletes have weakened hip strength and decreased muscle activation during loading such as when landing, this causes the hip muscles to adduct and rotate inwards resulting in knee valgus motion.
Females are more prone to injury compared to their male counterparts due to anatomical, hormonal and neuromuscular factors that differ between the sexes throughout maturation. Although some factors are un-modifiable it is best to focus on those we can, to ensure our young female netball athletes reduce their risk of injury and allow them to keep playing effectively and efficiently into the future. Encourage hamstring and gluteus maximus strengthening as well as proper landing techniques during training and game play to reduce neuromuscular deficits that contribute to injury risk.
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