by Elise Elsworth
Soccer is the most popular sport in the world (1), yet it carries one of the highest anterior cruciate ligament (ACL) injury rates (2).
The ACL is a ligament in the knee that contributes to knee stability by passively restraining the forward movement of the tibia on the femur. Passive restraints (ligaments, e.g. ACL, and bony morphology) alongside active restraints (muscle contraction and neuromuscular timing) give the knee its stability whilst completing activities such as running, cutting and pivoting – all of which are essential elements of gameplay in soccer.
There are approximately 350,000 ACL reconstructions each year in the US alone (3). One Australian study has reported a 74% increase between 2000 and 2015 in ACL reconstructions for those less than 25 years of age (4).
ACL injuries take significant time to rehabilitate and are immediately disabling to the athlete. They carry large financial and time burdens and affect quality of life both physically and psychologically. ACL injuries result in atypical strength, balance, proprioceptionA and neuromuscular control, in addition to increasing the risk of knee osteoarthritis; 78% develop osteoarthritis (5) and 13-15% require a total knee replacement in the future (2). Closely associated with complete ACL ruptures is damage to the menisci and bony surfaces in the knee (6), and 20% suffer re-injury within 2 years (7).
ACL injury risk is influenced by poor landing biomechanics and muscular activation, fatigue, high BMIB, and various anatomical morphology and alignment variations (6,8,9). Most at risk of ACL injury are those between the ages of 15 to 25 (7).
Female athletes are 2-8 times more likely than their male counterparts to sustain non-contact ACL injuries (6) due to factors that are:
Increased pelvic width and greater Q angleC;
Fluctuations in oestrogen, progesterone and relaxin during the menstrual cycle altering ligamentous laxity (6); and
Increased knee valgusD motion and hip internal rotation during landing, reduced knee flexion during landing, increased quadriceps muscle activation (6,8,9).
80% of ACL injuries are sustained in a non-contact manner (7), which highlights the preventable nature of most ACL injury mechanisms. As such, there has been great interest in injury prevention programs (IPPs) for the reduction of ACL injuries.
IPPs typically include three main elements (6,7,10,11,):
1. Plyometric exercises:
The focus is on correct technique and body mechanics;
2. Neuromuscular training:
Aims to improve and create optimal patterns of muscle firing, increase joint stability dynamically, and to perform sport- and daily activity- specific skills and patterns of movement; and
3. Strength training:
Shown to be effective when completed in conjunction with neuromuscular and plyometric training (7).
Nessler, Denney and Sampley (2017) report that there are 6 critical principles of ACL IPPs; these are:
Prevention programs should be implemented at an early age;
Addressing poor biomechanics is essential in reducing ACL injury risk – increased knee valgus is one of the most potent indicators of injury risk;
Compliance is typically poor. >66% compliance is related to an injury reduction rate of 82%, whereas <66% to 44%;
Studies generally state that sessions should be performed several times each week for between 20-30 minutes and commenced during preseason;
Feedback in the form of an external focus is superior to that of an internal focus. E.g. “point your knees towards the cones,” rather than “keep your knees over your toes.” This helps to create more enhanced and automatic motor control processes (reducing the reliance on conscious control) and creating superior results (10);
6. Exercise variety:
Programs that have plyometric, neuromuscular and strength training components are superior to single interventions.
Poor compliance with ACL IPPs, however, impedes the success of these programs (2). Barriers that contribute to clinical ineffectiveness include lengthy program duration (2), not altering the program to give variability (10), giving participating athletes a passive rather than active role (10), and negative feedback rather than positive feedback (10). Programs should also be sport-specific.
Implemented ACL IPPs have been shown in one study to decrease ACL injury rates by 51% (12), whilst another study reports up to 52% in females and 85% in males (7), and 70% for females when an IPP is carried out for more than 30 minutes each week, as reported by Gokeler et al. (2018). A recent study of the FIFA 11+ IPP (a 15-20 minute on-field dynamic warm-up aimed at general injury prevention) found a 77% decrease in ACL injury in collegiate male soccer players (13).
Whilst ACL injury is a daunting and time-consuming injury, there is increasing evidence in support of IPPs to decrease ACL injury risk. Your soccer club and/or physiotherapist should be integral in creating and implementing an effective IPP, focussing on plyometric, neuromuscular and strength training in order to reduce the risk of ACL injury.
A: Proprioception = the relative position of one’s body part
B: BMI = Body Mass Index
C: Q angle = the line of force of the quadriceps, measured from anterior superior iliac spine of the pelvis to the midpoint of the patella
D: Knee valgus = the knee angles in towards the midline of the body
1. FIFA Communications Division. FIFA big count 2006: 270 million people active in football. Zurich; 2007. Retrieved from:
2. Dai, B., Mao, D., Garrett, W.E., & Yu, B. (2014). Anterior cruciate ligament injuries in soccer: Loading mechanisms, risk factors and prevention programs. Journal of Sport and Health Science, 3, 299-306.
3. Davies, G.J., McCarty, E., Provencher, M., & Manske, R.C. (2017). ACL return to sport guidelines and criteria. Current Reviews in Musculoskeletal Medicine, 10(3), 307-314.
4. Zbrojkiewicz, D., Vertullo, C., Grayson, J.E. (2018). Increasing rates of anterior cruciate ligament reconstruction in young Australians, 2000-2015 (2018). Medical Journal of Australia, 208(8), 354-358.
5. Myklebust, G., Bahr, R (2005). Return to play guidelines after anterior cruciate ligament surgery. British Journal of Sports Medicine, 39, 127-131.
6. Mandelbaum, B.R., Silvers, H.J., Watanabe, D.S., Knarr, J.F., Thomas, S.D., Griffin, L.Y., … Garrett, W. (2005). Effectiveness of neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes. 2-year follow-up. The American Journal of Sports Medicine, 33(7), 1003-1010.
7. Nessler, T., Denney, L., & Sampley, J. (2017). ACL injury prevention: What does research tell us? Current Reviews in Musculoskeletal Medicine, 10, 281-288.
8. Smith, H. C., Vacek, P., Johnson, R.J., Slauterbeck, J.R., Hashemi, J., Shultz, S., & Beynnon, B.D. (2012). Risk factors for anterior cruciate ligament injury: A review of the literature – Part 1: Neuromuscular and anatomic risk (2012). Orthopaedic Surgery, 4(1), 69-78.
9. Hewett, T.E., Myer, G.D., & Ford, K.R. (2005). Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: A prospective study. The American Journal of Sports Medicine, 33(4), 492-501.
10. Gokeler, A., Benjaminse, A., Kerkhoffs, G., & Verhagen, E. (2018). Using principles of motor learning to enhance ACL injury prevention programs. Sports Orthopaedics and Traumatology, 34, 23-30.
11. Donnell-Fink, L.A., Klara, K., Collins, J.E., Yang, H.Y., Goczalk, M.G., Katz, J.N., & Losina, E. (2016). Effectiveness of knee injury and anterior cruciate ligament tear prevention programs: a meta-analysis (2016). Public Library of Science, 10(12), doi: 10.1371/journal.pone.0144063.
12. Meyer, S.E., Yamato, S.E., & Saragiotto, B.T. (2017). Knee injury and ACL tear prevention programmes (PEDro synthesis). British Journal of Sports Medicine, 51, 1161-1162.
13. Silvers-Granelli, H.J., Bizzini, M., Arundale, A., Mandelbaum, B.R., & Snyder-Mackler, L. (2017). Does the FIFA 11+ injury prevention program reduce the incidence of ACL injury in male soccer players? Clinical Orthopaedics and Related Research, 475, 2447-2455.