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.
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).
- 50-yard jog around court
- Walking quadriceps stretch
- Frankensteins (right/left foot reaching up towards left/right hand)
- Single-leg hip hinge
- Shuffles with alternating groin stretch
- High-knee pull to lung with trunk rotation
- Ten yard sideways run
- Ten yard backwards run
- Butt kicks to high knee runs
- Partner bumps with single-leg landings
- Partner zig-zag runs
- Double/single-leg triple jumps (repeat 3X)
- Five yard shuffle to 10-yard sprint (repeat 2X each side)
- 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.
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
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