Amongst the many team ball sports accessible to the youth of Australia, netball is one of the most popular sports for young Australian females. The nature of the game involves high intensity and high impact movements, which can impact the growing body of youth female athletes thus rendering them susceptible to injury. These movements often include rapid acceleration, deceleration, and changes in direction, whilst at times performing jumping and/or landing movements. As a result, young female netball athletes are more susceptible to injuries in the knee, particularly concerning their Anterior Cruciate Ligament. This important ligament is more commonly known as the ACL.
Female athletes are 4-6 times more likely to sustain an ACL injury than males. Young netball athletes can be predisposed to increased risk of ACL injury, due to a combination of structural, muscular, biomechanical and hormonal factors.
A common factor preventing ACL injury is in-effective co-activation of the hamstring and quadriceps muscle. Co-activation refers to two muscles activating in synchronization. These muscles support ligaments around the knee, assisting in reducing large external loads applied to the joint. Efficient quadriceps and hamstring co-activation protects the knee joint from risk factors such as knee abduction and valgus knee motion. This is commonly referred to as ‘knocked knees’ – a term you may have heard before, which is used to describe the act of the knees coming together and knocking in an unnatural manner.
Your quadriceps play an important role in straightening your knee, whilst your hamstrings bend your knee. Quadriceps to hamstring ratio measures the strength of the hamstrings compared to the quadriceps. A high ratio means the hamstrings are weaker than the quadriceps. During landing the hamstrings should activate beforehand to protect the ACL. Decreased hamstring strength limits the hamstrings ability to activate prior to landing, increasing valgus movement. While decelerating, the strength of the hamstring to quadriceps ratio is important for preventing valgus knee motion, or knocking of the knees, thus reducing the overall potential for ACL injury.
During and following puberty the hamstring to quadriceps strength ratio deficit starts to emerge in female athletes. Knee straightening strength increases but knee bending remains the same. Females generally have increased quadriceps activation and decreased hamstring activation when landing, running, side cutting and crosscutting. This means females usually land with reduced knee bend, remaining more straight legged due to pronounced quadriceps activation. This becomes a problem as majority of ACL injuries that occur are reported with knees close to full straightening. This increases load on the ACL, increasing risk of injury. If hamstrings cannot activate effectively, increased load is placed on the ACL thus increasing potential for knee valgus motion, putting the ACL at risk of injury.
High incidences of ACL injuries sustained by young female athletes demonstrate the need to implement effective injury prevention programs such as strength training to improve muscular strength, neuromuscular efficiency (the ability of the nervous system to recruit the correct muscles and produce force) and movement competency.
If you want to prepare your young female netball athletes for game intensity, athletic development, improve performance and prevent injuries it is important to implement an integrative and appropriately designed strength training program.
Programs involving resistance and plyometric training for young female netball athletes increase co-activation of the hamstring and quadriceps muscle group. Increased quadriceps and hamstring co-activation improves joint stability, movement efficiency and muscular control to prevent lower body injuries. This is important in supporting the ACL during movement and effective in reducing risk factors associated with ACL injury in female netball athletes. Such as improving knee bending and straightening range of movement (ROM) during landing as well as decreasing the ‘knocking knee’ movement.
It is optimal to introduce NMT to female netball athletes pre-adolescence as after age 14, female athletes may have developed altered joint mechanics due to the changes that occur during maturation. A combination of plyometric and resistance training is most effective for decreased ACL injury risk with more prominent results in female netball athletes under 18 years of age (1).
For the greatest preventative effects, under guidance of a qualified and experienced strength and conditioning coach, a strength training program inclusive of 2 or more sessions per week, for 30 minutes or more should be implemented. It is important to involve hamstring-strengthening exercises to counterbalance the anterior shear force (angled force on front of the knee) produced by quadriceps to protect the ACL.
Plyometric exercises that demonstrate improved hamstring strength that should be included involve exercises such a depth jumps, single leg hurdle hops, single leg push off, broad jumps and split squat jumps (2). Resistance exercises should also be included for the lower body such as back squat, lunges, barbell split squats and of particular importance to the hamstring muscles the Romanian deadlift, Nordic lowerings, glute bridges and hip thrusts.
Technique focus during NMT programs is crucial and load should only be increased if movement in each exercise is performed correctly. Incorporating and emphasizing deep knee flexion during plyometric and strength exercises significantly improves knee bending during landing as they involve greater recruitment of the hamstrings (3).
If you want to see results in the reduction of ACL injuries in your young female netball athletes, compliance and applying progressive overload (incremental loading of exercises over a period of time) are essential to facilitate long-term physical adaptation.
In summary, the occurrence of ACL injuries can be reduced drastically in young female netball athletes by increasing hamstring strength.
- Myer GD, Sugimoto D, Thomas S, and Hewett TE. The Influence of Age on the Effectiveness of Neuromuscular Training to Reduce Anterior Cruciate Ligament Injury in Female Athletes: A Meta-Analysis. The American Journal of Sports Medicine 41: 203-215, 2013.
- Struminger, A. H., Lewek, M. D., Goto, S., Hibberd, E., & Blackburn, J. T. (2013). Comparison of gluteal and hamstring activation during five commonly used plyometric exercises. Clinical biomechanics, 28(7), 783-789.
- Myer GD, Ford KR, Palumbo J, and Hewett TE. Neuromuscular Training Improves Performance and Lower Extremity Biomechanics in Female Athletes. Journal of Strength & Conditioning Research 19: 51-60, 2005.