Beyond the Sets and Reps: An Introduction.

Therein lies a correlation between the brain and body that is a direct result of an interdisciplinary approach to understanding sports science. Beyond the programming is an interaction of disciplines closely examining the chaotic nature of our being. With The Rebel Movement blog, our mission is to investigate and further the science and philosophy of motor performance. Through our collaborative approach of skill acquisition and movement analysis, we will provide thought-provoking content applicable to athletes, coaches, researchers, and practitioners.  Your feedback is vital to the blog’s mission, so please feel free to provide your thoughts, comments, and considerations. We look forward to building a stronger foundation for the sports science community.

– Harjiv and Jason

Strategies to Reduce ACL Injury Risk in Youth Athletes – Part 2 (Strength Training)

In part 1 of our series on reducing ACL injuries in adolescent athletes, I discussed the mechanisms leading to the injury itself and warm-up strategies to reduce injury risk (https://rebelmovement.org/2019/04/25/strategies-to-reduce-injury-risk-in-youth-athletes-part-1/).

Part 2 will discuss strength training, including:

– what does the research state on strength training and injury?

– what are some fundamental resistance exercises that an adolescent athlete should be introduced to and perform?

– what is a proper way to regress / progress a strength exercise?

Let’s dive in…

Strength Training

 In my opinion, the introduction of sports into a youth’s life should coincide with an introduction to strength training. You may be thinking, “my (insert age) child should be lifting weights? Isn’t that dangerous?” It’s actually quite the opposite. Under proper supervision, a strength training program may offer an adolescent athlete a multitude of physical, emotional, and psychological benefits (Faigenbaum, 2009). Overall, it appears that 8-12 weeks of resistance training can improve overall strength by 30-50% in youth athletes (Dehab & McCambridge, 2009).

(Faigenbaum, 2009)

For the sake of scope, let’s focus our attention on the effects of strength training for reducing injury risk in this population. So what does the research tell us? One of the earliest studies completed on strength training and injury rate was by Hejna (1982). High school athletes were divided into three groups: weight training during the pre-season and in-season, weight training year-round, and a control, non-strength training group. The researchers found that athletes who participated in weight training had an injury rate of 26.2%, while the control group’s injury rate was 72.4%. If an injury were to occur, the control group took approximately 2.4 times longer to rehabilitate from injury compared to their strength training counterparts.

After 8 weeks of resistance and plyometric training, 27 female high school athletes demonstrated improvements in neuromuscular and biomechanical movement qualities that suggest these athletes were at less risk for ACL injury (Lephart, 2005). Specifically, the athletes demonstrated increases in quadriceps strength during dynamometer testing and greater muscular activity in the gluteus medius bilateral vertical jump (Lephart, 2005). Additionally, athletes displayed increased hip and knee flexion during the jump-landing maneuver (Lephart, 2005). In a meta-analysis by Sugimoto (2015), across 14 reviewed studies, strength interventions reduced the risk of ACL injury by 68% in youth female athletes. A larger meta-analysis by Lauersen, Bertelsen, & Andersen (2014) provide additional evidence for strength training to reduce injury risk, as “strength training reduced sports injuries to less than 1/3 and overuse injuries could be almost halved”. So the question becomes, what specific strength exercises should youth athletes complete? From multiple investigations, it appears that even the addition of bodyweight exercises can have a significant impact on injury risk. Keep in mind that bodyweight exercises are a form of resistance training! Walden (2012) incorporated unilateral/bilateral squats, glute bridges, lunges, planks, and jump-landings, resulting in a 64% reduction in ACL injury. Similar exercises were incorporated into a warm-up for female youth soccer athletes, resulting in a 77% reduction in knee injury rate (Kiani, 2010).

(Walden, 2012)

The basis of strength training for adolescent athletes is mastering basic movement patterns that are transferable to a multitude of more complex resistance exercises. We want to ensure that our athletes are not adding strength to dysfunction, which can lead to many future issues. A requisite for every adolescent (and any athlete for that matter) is demonstrating proper form in the following “fundamental” exercises: hip-hinge / Romanian deadlift, body-weight squat, forward/backward lunge, push-up, pull-up/inverted row, and over-head press.

In addition to form, proper exercise progression is a must for younger athletes, as these motor patterns are very much malleable and quickly receptive to adaptation, for better or worse. Here’s an example of a squat exercise progression that I have found quite successful with youth athletes:

1) hip-hinge

2) body-weight squat (may add box behind athlete)

3) squat with a PVC pipe

4) goblet and/or resistance band squat

5) unloaded barbell back/front squat

6) loaded barbell back/front squat

Again, I cannot stress the following enough: do not add strength to dysfunction. If your athlete cannot adequately perform a barbell squat, there is no benefit to adding further load to this movement. Similar progressions can be made for any upper or lower body compound exercise. Sometimes that will include the use of resistance bands or partners (e.g. assisted pull-ups), TRX equipment (single-leg squats, inverted rows), or the training center itself (wall assisted push-ups). To reap the most benefits of strength training program, youth athletes should be participating in a strength program at twice per week at a minimum (Behm, 2008). It is beyond the scope of this post to discuss the physiological adaptations to resistance training, but athletes need to be consistent in their training to obtain build resiliency within the musculoskeletal system. Loading the system in a sensible and progressive manner throughout our young athletes’ sporting careers will provide the opportunity for maximal performance, but more importantly, will keep them on the field.

If you’re looking to dive deeper into the literature regarding strength training for adolescent athletes, I highly recommend these position papers:

National Strength and Conditioning Association – https://www.ncbi.nlm.nih.gov/pubmed/19620931

Canadian Society for Exercise Physiology – https://www.ncbi.nlm.nih.gov/pubmed/18461111

UK Strength and Conditioning Association – https://www.ncbi.nlm.nih.gov/pubmed/24055781

References

Behm, D. G., Faigenbaum, A. D., Falk, B., & Klentrou, P. (2008). Canadian Society for Exercise Physiology position paper: resistance training in children and adolescents. Applied Physiology, Nutrition, and Metabolism33(3), 547-561.

Dahab, K. S., & McCambridge, T. M. (2009). Strength training in children and adolescents: raising the bar for young athletes?. Sports Health1(3), 223-226.

Faigenbaum, A. D., Kraemer, W. J., Blimkie, C. J., Jeffreys, I., Micheli, L. J., Nitka, M., & Rowland, T. W. (2009). Youth Resistance Training: Updated Position Statement Paper From the National Strength and Conditioning Association. Journal of Strength and Conditioning Research,23(Supplement 5), S60-S79. doi:10.1519/jsc.0b013e31819df407

Hejna, W. F., Rosenberg, A., Buturusis, D. J., & Krieger, A. (1982). The Prevention of Sports Injuries in High School Students Through Strength Training. National Strength Coaches Association Journal,4(1), 28-31. doi:10.1519/0199-610x(1982)0042.3.co;2

Kiani, A. (2010). Prevention of Soccer-Related Knee Injuries in Teenaged Girls. Archives of Internal Medicine,170(1), 43-49. doi:10.1001/archinternmed.2009.289

Lauersen, J. B., Bertelsen, D. M., & Andersen, L. B. (2014). The effectiveness of exercise interventions to prevent sports injuries: a systematic review and meta-analysis of randomised controlled trials. British Journal of Sports Medicine48(11), 871-877.

Lephart, S. M., Abt, J. P., Ferris, C. M., Sell, T. C., Nagai, T., Myers, J. B., & Irrgang, J. J. (2005). Neuromuscular and biomechanical characteristic changes in high school athletes: a plyometric versus basic resistance program. British Journal of Sports Medicine39(12), 932-938.

Sugimoto, D., Myer, G. D., Foss, K. D., & Hewett, T. E. (2015). Specific exercise effects of preventive neuromuscular training intervention on anterior cruciate ligament injury risk reduction in young females: Meta-analysis and subgroup analysis. British Journal of Sports Medicine,49(5), 282-289. doi:10.1136/bjsports-2014-093461

Walden, M., Atroshi, I., Magnusson, H., Wagner, P., & Hagglund, M. (2012). Prevention of acute knee injuries in adolescent female football players: Cluster randomised controlled trial. BMJ,May 3(344). doi:10.1136/bmj.e3042

 

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The Rebel Movement Podcast (Episode 2) – ACL and the Brain: From Research to Application

We had a great time chatting away last night on ACL injury, prevention, rehabilitation and more! We had a privilege to talk through the lens of our own disciplines (biomechanics and motor learning). Let us know what you like, dislike, and how we can improve. As always, if you’d like to write for our blog, please reach out to either one of us!

Article Links:

It’s Not the Drills

Random IMPACT

By BJ LeRoy

  • At coaching clinics, the pens whip out when the speaker demonstrates a new drill. Everyone is anxious to write down that drill that will make the big difference. 
  • Countless times, high level coaches are asked, “What drill can we do to fix our …” 
  • Doug Beal and Russ Rose have been asked about what drills they use. In similar answers, both profess to use only a few drills with many variations. 

What are the magic drills that make those teams so good? 

Big secret; it’s not the drills. There is no magic.

If simply running the drills made you great, everyone could buy Al Scates drill book (like I did once upon a time) and we’d all be awesome, because his teams were awesome. Blindly running Coach Scates’ drills didn’t make a difference for my team. If his drills didn’t work, whose would? 

Looking at it another way; two great teams run different drills, and they end up playing each other in the championship. How can different drills work in attaining the same goal? 

Certainly athletes make a difference. Some years you have superior athletes and you win. Some years you have great players yet you lose to superior talent. Let’s set talent aside for a bit, despite that having superior players is likely the most important ingredient to winning matches. 

If it’s not the drills, what is it? 

Probably a mix of a few common principles, applied to everything in the program. A few to start with; 

  • Understanding. The players learn to understand why they are using a skill, running a drill, doing things in a specific way. I hear and I forget. I see and I remember. I do and I understand.
  • Specificity. Hundreds of top coaches say this repeatedly; you need to practice what you want to do. EXACTLY what you want to do. Coaches don’t toss in games; players don’t hit under the net; there are very few perfect passes. When game-time comes, you will have to pass, set, hit, dig and block every odd thing that comes your way. So it must be practiced that way; randomly.
  • Flexibility. Sometimes, you might win with serving. Sometimes with defense. Maybe with outside hitting. Playing to your strengths (whether your favorite skill or not) is your best strategy. Also flexibility within a drill; one drill with many options is better than 20 drills with no options. They already know the drill, you’ve just tweaked it to work on the thing you need most. Finally, flexibility with a system. You may not have the players to run the system you like; you need to run the system that suits the players. 
  • Continuous learning. Mick Haley chose to speed up USC’s offense. Russ Rose chose to swing block (and then didn’t, and then did again.) He is reportedly an avid reader. John Dunning shuffled his lineup and changed systems after losing a key player. If those guys are still learning, can’t we all?

Most importantly, we need our teammates on the same page. Good teams have a system for siding out, playing in transition, serving, defense, and for being out-of-system. They work together. And they understand what their teammates are going to do in each of those playing systems. When you have common ground and understanding of everyone else’s role, your role makes sense, and you can perform it, or change it to fit what the opponent is throwing at you. Drills might guide teams toward working on a specific skill; the team’s common ground lends to success in any drill. 

There are certainly drills that are better than others. Specific and game-like and random are a good start. Great teams can get better in any drill with those ingredients, because they have taken the time to learn the “whys”, and to understand.

  • Why does this work
  • How can I know something sooner
  • Why does this happen after that happened
  • Why do I need to be here, not there

Carl McGown liked to say, teach them where to look, and teach them how to move. Shortly after, if not woven into those tasks, you have to learn why. If you know why it works, you likely already have the drills you need to succeed.  

Random IMPACT is a bi-monthly education column in the Badger Beacon, an award-winning newsletter published by the Badger Region. 

BJ LeRoy is a CAP Cadre member, board member and coach from the Badger Region. He also helps administer the Facebook group Volleyball Coaches and Trainers. You can reach BJ at 4bjleroy@gmail.com. 

The Rebel Movement Podcast (Episode 1) – Knowledge Translation; sesquipedalian

It’s official! we’ve started our podcast!

In our first podcast episode, Harjiv and I discuss knowledge translation from the perspective of 2 PhD students.

Here are a few useful links discussing knowledge translation in the health care system.

Defining knowledge translation: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2717660/

Getting the word out: New approaches for disseminating public health science: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794246/

The acceptability among health researchers and clinicians of social media to translate research evidence to clinical practice: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4468567/

The answer is 17 years, what is the question: Understanding time lags in translational research: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3241518/

How long does biomedical research take? Studying the time taken between biomedical and health research and its translation into products, policy, practice: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3241518/

Knowledge translation in health care: A concept analysis: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4301207/

Hope you all enjoy this one. We’ve got plenty more lined up, stay tuned. Once again, if you’d like to write for our blog, feel free to email either one of us. If you have any comments, suggestions, or concerns, please feel free to contact us. Thanks!

 

 

 

Must Reads…and Some Classics

Here’s a list of five accessible articles we thought are a good start, must read, and of course are classics within the Biomechanics and Motor Learning literature. Throughout the year, we’ll continue to share articles grouped within themes that are applicable to all.

 

Motor Learning

  1. A Schema Theory of Discrete Motor Skill Learning
  2. Motor Skill Acquisition – K.M. Newell
  3. The Theory of Affordances
  4. A REVIEW OF THE CONTEXTUAL INTERFERENCE EFFECT IN MOTOR SKILL ACQUISITION
  5. Optimizing performance through intrinsic motivation and attention for learning: The OPTIMAL theory of motor learning

Biomechanics

  1. Kinematics vs. Kinetics 
  2. Inverse Dynamics
  3. THE PITFALLS OF 2D “BIOMECHANICAL” ANALYSIS
  4. A Guide for Coaches Looking to Invest in Force Plates
  5. Blog » Building Lateral Strength to Correct Crossover Gait Building Lateral Strength to Correct Crossover Gait

 

If you’d like to write for our blog, please feel free to reach out to either Jason or Harjiv.

 

The pen is the most powerful weapon in the world.

When we started the Rebel Movement, we wanted to use it as an avenue to write, share, dialogue, and most importantly, engage the world around us through a different form of media. In fact, we also saw it as a way to make mistakes. The fact is that we all have opinions, ideas, and thoughts, but struggle to find the medium to share such expressions within a post that is barred by character limitations.

This is an open call to anyone interested in writing. Please get in touch! Let’s truly harness the interdisciplinary nature of this art.

Here are some blog posts we have written for other great platforms.

Jason Avedesian 

Perform-X Training Systems – The Jump X

Harjiv Singh

Just Fly Sports- “Reorganizing the Athlete’s Brain”

Science for Sport – “Skill Acquisition”

 

 

Strategies to Reduce ACL Injury Risk in Youth Athletes – Part 1 (The Warm-Up)

While there are numerous benefits to youth sport participation, it is imperative that clinicians and practitioners address the risk of injury that may occur. I want to make it clear that my intention for this post is not to deter individuals from participation in the well-documented positive outcomes of youth sport, but to make those involved aware of a few mechanisms surrounding potential injury. Mechanisms that when addressed early and in the correct fashion, can lead to a lifetime of many positive health outcomes.

My goal is to create an interactive database applicable to practitioners, coaches, and parents. Ultimately, they are the ones with the opportunity to implement these strategies with their athletes. Through a variety of media modalities, I plan to release a new angle on strategies for anterior cruciate ligament (ACL) injury risk reduction each month or so. I have an outline of how I would like to release this information, but would love to continue to build on these posts based on feedback. As always, please reach out if there is something you would like to discuss or you think would be pertinent information for this project. Input and collaboration, big or small, will ultimately allow us to solve some of the issues surrounding ACL injury in youth sports.

Across multiple posts throughout the summer, I am going to discuss and explore a variety of strategies that may be useful in keeping your youth athletes on the field. My past and present research focuses on ACL injury mechanisms in various sporting populations, so I’ll focus the majority of my attention on strategies to reduce this risk. ACL injury has become a major concern within youth athletics that may significantly alter ones sporting career and overall well-being. In my experience, many coaches and parents are initially unaware of strategies to mitigate ACL injury risk in their children. There tends to be a reliance on ‘over-competing’ and ‘under-training’, with little thought given to feasible warm-up, strength training, nutritional, psychological, and sleep strategies to reduce ACL injury risk. What is particularly troubling is that the rate of ACL injury in adolescent athletes (ages 6-18) has risen by 2.3% over a 20 year period (Beck, 2016). This may be attributed to a combination of many factors including (but not limited to): early sport specialization (Bell, 2018), insufficient recovery from sport/life stressors, and inadequate/non-compliant fitness preparation and training (Soligard, 2010).

——————————————————————————————————

Before diving into ways to reduce injury risk, let’s start with the ACL itself. A major structure of the knee joint, the ACL plays a crucial role in stabilizing the knee during motion and allowing the lower leg to move through its normal range-of-motion. With one of the largest mechanoreceptor concentrations in the lower extremity, the ACL provides vital proprioceptive information to the central nervous system when the knee is in motion (Decker, 2011). An ACL injury can be classified as a contact or non-contact injury, and an estimated 70% of sport-related injuries take place in non-contact situations (Griffin, 2000). A non-contact ACL injury often occurs when an athlete performs a sudden landing, deceleration, or cutting maneuver (Griffin, 2000). During these maneuvers, athletes may injure the ACL when the knee is near full extension, ranging from 10-30 degrees of knee flexion (Boden, 2000). Further observation of knee motion during sporting movements has led researchers to believe excessive frontal plane motion may also contribute to ACL injury (Grandstrand, 2006), however, it is likely that an injury to the ACL is multiplanar in nature (Shimokochi, 2008). This includes excessive anterior tibia motion (Shimokochi, 2008), high knee rotational torque (Quatman, 2009), and valgus collapse (Quatman, 2009) that potentially lead to an ACL sprain or tear. Along with biomechanical factors, neuromuscular movement patterns such as increased activation of the quadriceps musculature places significant strain on the ACL at low knee flexion angles (Markolf, 2004). The ACL is at an increased risk of injury when excessive quadriceps forces are combined with excessive multiplanar knee motions (Shimokochi, 2008).

——————————————————————————————————

In Part 1 of this series, I figure we begin with the most intuitive prevention strategy, one that I spent two years studying during my master’s degree, and one that often gets inadequate focus: the warm-up.

Warm-Ups

During competition, an athlete may be subjected to repetitive high force patterns and unpredictable movements, potentially leading to increased ACL injury risk, and evidence indicates the majority of ACL injuries take place in game situations (Bradley, 2002) under noncontact conditions. The timing of ACL injuries has not been extensively examined, but some researchers propose that an athlete may be at an increased risk of injury under a fatigued state (Borotikar, 2008). However, a review of fatiguing protocols on lower limb biomechanics revealed varying effects of fatigue on knee mechanics during athletic tasks (Barber-Westin, 2017), suggesting fatigue may not heighten ACL injury risk. While the effects of fatigue on ACL injury is inconsistent, more recent evidence indicates that athletes are injuring the ACL earlier in competition. A study from the NBA reported that the first quarter accounted for the second highest ACL injury incidence (24%), compared to 13%, 22%, and 40% in the second, third, and fourth quarter, respectively (Harris, 2013). A video-based analysis of male soccer ACL injury mechanisms and situations revealed that 26% of injuries occurred within the first nine minutes of match play, leading investigators to speculate the effects of insufficient physical preparation prior to the match (Grassi, 2017). In a three-cohort study of professional soccer players, 57% of ACL injuries occurred in the first half of matches and approximately 22% in the first 15 minutes of match time (Waldén, 2011).  Furthermore, the majority of ACL injuries in female soccer athletes were sustained within the first 15 minutes of each half, leading the authors to speculate the effects of warm-up on ACL injury between sexes (Waldén, 2011).

In order to adequately prepare their bodies for activity, youth athletes should participate in warm ups prior to any training or competitive event. While there are many warm-up modalities, you may find yourself asking, what are best warm-up practices to reduce ACL injury risk? Research indicates that an adequate warm-up consists of the following: 1) whole-body and multidirectional dynamic movements, 2) movement progression from general to sport-specific and 3) completed within 15-20 minutes (Barengo, 2014). A study from Olsen (2005) determined that a warm-up consisting of the above-mentioned modalities reduced the risk of acute ankle and knee injuries by approximately 50% in adolescent athletes. Similarly, Mandelbaum (2005) revealed that ACL injury decreased by 74-88% in adolescent female soccer players following a warm-up of general exercise, plyometric activity, soccer-specific drills, and light stretching. A more recently developed and popular warm-up among soccer athletes is the FIFA 11+ program. The FIFA 11+ takes approximately 20 minutes to complete and requires minimal equipment, with the warm-up itself consisting of partner running, jump-landings, and core stabilization drills. A recent review concluded that the FIFA 11+ demonstrates a 30% reduction in the risk of injury in adolescent soccer athletes (Sadigursky, 2017).

I took the warm-up research a step further during my Master’s degree at Ball State University. My thesis examined the acute effects of two different warm-up strategies on single-leg landing mechanics in female volleyball athletes. The athletes came to the laboratory for two testing sessions, performing a 1) dynamic stretching warm-up and 2) dynamic + static stretching warm-up. Landing biomechanics were examined across three time points (pre warm-up, 1 minute post warm-up and 15 minutes post warm-up). I found that athletes demonstrated greater torque (abduction moment) on the non-dominant knee following a warm-up that included dynamic + static stretching. I postulated that increased muscular compliance and decreased force generating capabilities of the hamstrings and glutes after static stretching were potential mechanisms leading to higher risk landing patterns (Avedesian, 2019). In summary, athletes were better off performing a dynamic warm-up without static stretching when assessing landing biomechanics associated with ACL injury risk.

To give another example, let’s run through an example of what a strong, foundational warm-up would look like for an adolescent jump-landing athletes (i.e., basketball, volleyball, soccer).

  1. 50-yard jog around court
  2. Walking quadriceps stretch
  3. Frankensteins (right/left foot reaching up towards left/right hand)
  4. Single-leg hip hinge
  5. Shuffles with alternating groin stretch
  6. High-knee pull to lung with trunk rotation
  7. Ten yard sideways run
  8. Ten yard backwards run
  9. Butt kicks to high knee runs
  10. Skip-hops
  11. Partner bumps with single-leg landings
  12. Partner zig-zag runs
  13. Double/single-leg triple jumps (repeat 3X)
  14. Five yard shuffle to 10-yard sprint (repeat 2X each side)
  15. Two countermovement jumps to 10-yard sprint with active deceleration (repeat 3X)

(Note: instruct the athletes to jog back to the starting position upon completion of each exercise, all exercises can be completed within 10-15 yards).

The provided warm-up examples can be easily implemented into any practice regimen and can even create a teambuilding experience if run by the athletes themselves once proficiency is demonstrated. The coaches should be watching and providing feedback and instruction as necessary. But the sense of ownership and autonomy from athlete-led warm-ups may increase compliance in the long-term (Gillet, 2010). This is important because adherence to these protocols must be high in order to see the benefits in injury risk reduction. In examining compliance to an injury-specific warm-up, Soligard (2010) found that high compliance teams (competing warm-up in 70% of training/competition) demonstrated a 35% reduction in injury risk compared to teams with intermediate compliance (warm-up completion in 42% of training/competition).

So, to wrap everything up from this post.

1) ACL injury risk is high in adolescent athletes

2) The majority of ACL injuries occur under non-contact situations and often early in competition

3) Warm-ups with high adherence that include dynamic activity and sport-specific exercise may reduce the risk of ACL injury

Now that we have discussed warm-up implementation, let’s shift to considerations for strength training. Part 2 coming soon.

– Jason

Twitter: @JasonAvedesian

Email: jason.avedesian@unlv.edu

References

Avedesian, J. M., Judge, L. W., Wang, H., & Dickin, D. C. (2018). Kinetic Analysis of Unilateral Landings in Female Volleyball Players After a Dynamic and Combined Dynamic-Static Warm-up. Journal of Strength and Conditioning Research. doi:10.1519/jsc.0000000000002736

Barber-Westin, S. D. & Noyes, F. R. (2017). Effect of Fatigue Protocols on Lower Limb Neuromuscular Function and Implications for Anterior Cruciate Ligament Injury Prevention Training. Am. J. Sports Med. 363546517693846. doi:10.1177/0363546517693846

Bell, D. R., Post, E. G., Biese, K., Bay, C., & Mcleod, T. V. (2018). Sport Specialization and Risk of Overuse Injuries: A Systematic Review With Meta-analysis. Pediatrics,142(3). doi:10.1542/peds.2018-0657

Beck, N. A., Lawrence, J. T., Nordin, J. D., Defor, T. A., & Tompkins, M. (2016). ACL Tears in School-Aged Children and Adolescents: Has There Been an Increased Incidence over the Last 20 Years? Pediatrics,137(Supplement 3). doi:10.1542/peds.137.supplement_3.554a

Boden, B. P., Griffin, L. Y. & Garrett, W. E. (2000). Etiology and Prevention of Noncontact ACL Injury. Phys. Sportsmed. 28, 53–60.

Borotikar, B. S., Newcomer, R., Koppes, R. & McLean, S. G. (2008). Combined effects of fatigue and decision making on female lower limb landing postures: central and peripheral contributions to ACL injury risk. Clin. Biomech. 23, 81–92.

Bradley, J. P., Klimkiewicz, J. J., Rytel, M. J. & Powell, J. W. (2002). Anterior cruciate ligament injuries in the National Football League: epidemiology and current treatment trends among team physicians. Arthrosc. J. Arthrosc. Relat. Surg. Off. Publ. Arthrosc. Assoc. N. Am. Int. Arthrosc. Assoc. 18, 502–509.

Decker, L. M., Moraiti, C., Stergiou, N. & Georgoulis, A. D. (2011). New insights into anterior cruciate ligament deficiency and reconstruction through the assessment of knee kinematic variability in terms of nonlinear dynamics. Knee Surg. Sports Traumatol. Arthrosc. Off. J. ESSKA 19, 1620–1633.

Gillet, N., Vallerand, R. J., Amoura, S., & Baldes, B. (2010). Influence of coaches autonomy support on athletes motivation and sport performance: A test of the hierarchical model of intrinsic and extrinsic motivation. Psychology of Sport and Exercise,11(2), 155-161. doi:10.1016/j.psychsport.2009.10.004

Grandstrand, S. L., Pfeiffer, R. P., Sabick, M. B., DeBeliso, M. & Shea, K. G. (2006). The effects of a commercially available warm-up program on landing mechanics in female youth soccer players. J. Strength Cond. Res. 20, 331–335.

Grassi, A. et al. (2017). Mechanisms and situations of anterior cruciate ligament injuries in professional male soccer players: a YouTube-based video analysis. Eur. J. Orthop. Surg. Traumatol. Orthop. Traumatol. doi:10.1007/s00590-017-1905-0

Griffin, L. Y. et al. (2000). Noncontact anterior cruciate ligament injuries: risk factors and prevention strategies. J. Am. Acad. Orthop. Surg. 8, 141–150.

Harris, J. D. et al. (2013). Return-to-Sport and Performance After Anterior Cruciate Ligament Reconstruction in National Basketball Association Players. Sports Health 5, 562–568.

Hejna, W. F., Rosenberg, A., Buturusis, D. J., & Krieger, A. (1982). The Prevention of Sports Injuries in High School Students Through Strength Training. National Strength Coaches Association Journal,4(1), 28-31. doi:10.1519/0199-610x(1982)0042.3.co;2

Lauersen, J. B., Bertelsen, D. M., & Andersen, L. B. (2014). The effectiveness of exercise interventions to prevent sports injuries: A systematic review and meta-analysis of randomised controlled trials. British Journal of Sports Medicine,48(11), 871-877. doi:10.1136/bjsports-2013-092538

Mandelbaum, et al. (2005). Effectiveness of a Neuromuscular and Proprioceptive Training Program in Preventing Anterior Cruciate Ligament Injuries in Female Athletes. The American Journal of Sports Medicine,33(7), 1003-1010. doi:10.1177/0363546504272261

Markolf, K. L., O’Neill, G., Jackson, S. R. & McAllister, D. R. (2004). Effects of applied quadriceps and hamstrings muscle loads on forces in the anterior and posterior cruciate ligaments. Am. J. Sports Med. 32, 1144–1149.

Olsen, O., Myklebust, G., Engebretsen, L., Holme, I., & Bahr, R. (2005). Exercises to prevent lower limb injuries in youth sports: Cluster randomised controlled trial. BMJ,330(7489), 449. doi:10.1136/bmj.38330.632801.8f

Sadigursky, D., Braid, J. A., Lira, D. N., Machado, B. A., Carneiro, R. J., & Colavolpe, P. O. (2017). The FIFA 11 injury prevention program for soccer players: A systematic review. BMC Sports Science, Medicine and Rehabilitation,9(1). doi:10.1186/s13102-017-0083-z

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