Overview

Neuromuscular control is defined as an unconscious trained response of a muscle to stimuli regarding dynamic joint stability. It is a complex system of muscle activities including contraction, coordination, stabilization, postural control, and balance. In sports, neuromuscular control is crucial to perform jumping, landing, and pivoting tasks correctly and without injury. Neuromuscular control has been identified as an important factor when considering the differences in ACL injury risk and knee stability between males and females. Differences in muscle control, muscle activation, and movement patterns in male and female athletes have been implicated in the increased risk for ACL injury in female atheltes. ^, There have been many studies that describe these kinematic and biomechanical variations in sport movement patterns among males and females. For example, Chappell et al. investigated the “stop-jump” maneuver in particular and found that female athletes prepared for landing with decreased hip and knee flexion, increased quadriceps activation, and decreased hamstring activation, leading to increased ACL loading during landing when compared with males. Additionally, Ford et al. found that in middle- and high-school basketball players, females demonstrated greater knee valgus than males during a “jump-stop unanticipated cut” maneuver ( Fig. 5.1 ).

Landings from “Stop-jump” Maneuver.

The load-bearing axis (indicated in white) on the lower limbs in this maneuver can be represented by a line extending from the center of the femoral head to the center of the ankle joint. (A) Landing with knee valgus. Here the load-bearing axis passes laterally to the knee increasing force in the lateral compartment. (B) Neutral landing where patient’s load-bearing axis passes directly through the center of the knee. (C) Landing with knee varus. Here the load-bearing axis passes medially to the knee increasing force in the medial compartment. In varus landing, knees lie outside the hip and ankle line.

It has been shown that neuromuscular risk factors are modifiable through NMT, which can lead to decreased risk for injury and increased sport performance. In a study by Myer et al., NMT protocols that utilized both plyometric and dynamic balance tasks were studied in high-school female athletes. The investigators measured power, balance, strength, and landing force before and after training. The female athletes were all able to decrease their standard deviation of center of pressure during hop landing tests, as well as increased hamstring strength and vertical jump measurements, after a three times per week NMT program for 7 weeks.

The kinematic demands of sports differ and thus may be an important consideration when implementing NMT programs. As the majority of female ACL injuries stem from noncontact movements (i.e., cutting and pivoting maneuvers or jump landings), the frequency of these movements in their respective sports should be taken into account. For example, in a study by Cowley et al. the researchers assessed differences in cutting and landing tasks among high-school female basketball and soccer players and concluded that sport-specific NMT may be warranted with soccer players focusing on training for pivot and cutting movements and basketball players on jumping and landing mechanics. In a 2014 systematic review by Michaelidis et al. ACL injury prevention programs were assessed on their effectiveness in different sports. The authors concluded that training programs for soccer and handball athletes require sport-specific agility training, while jump-focused sports, such as basketball, should involve high-intensity plyometrics.

Historically, NMT programs have included a mix of strength training, plyometrics, balance exercises, and stretching to address muscle imbalances and develop control over muscle activation. Many studies have confirmed that NMT and injury prevention programs are a cost-effective strategy. In a 2018 study by Lewis et al., ACL injury prevention programs prevented 3764 lifetime ACL ruptures per 100,000 individuals (i.e., a 40% reduction in ACL injuries). Subsequent cases of osteoarthritis and total knee replacement procedures are also averted through the utilization of ACL prevention programs. Marshall et al. also investigated the economic impact of NMT programs compared to traditional warm-up strategies in youth soccer. A 38% reduction in injury risk and a 43% reduction in healthcare costs was found in the NMT group compared to the control. The authors projected that in 58,100 youth soccer players, an estimated $2.7 million in healthcare costs could be avoided over the duration of one season of implementation of an NMT program. Although NMT programs have been determined cost-effective, there is still considerable variation among programs, warranting an analysis of the most common and effective components of these prevention strategies. In the following section, common and effective components of ACL injury prevention programs will be reviewed.

Neuromuscular Training Program Characteristics

In 2018, the American Academy of Sports Physical Therapy published clinical practice guidelines for exercise-based knee and ACL injury prevention. They recommend a number of specific programs for reducing ACL injuries in athletes, including but not limited to HarmoKnee, Prevent Injury and Enhance Performance (PEP) program, and Sportsmetrics ( Table 5.1 ). These exercise-based prevention programs employ numerous intervention strategies, including proprioceptive training, NMT, strengthening exercises, stretching, agility, and plyometric exercises. Additionally, many programs employ instructors or coaches to give feedback to athletes on their performance of specific movements and exercises, particularly jump landing movements. ^,

In the 2019 meta-analysis and systematic review on ACL prevention programs for female athletes, the authors utilized robust quantitative and statistical methods to develop best-practice guidelines and elucidate the most effective components of various prevention programs. A total of 18 studies were included in the final analysis. Investigators determined that all NMT programs included some form of implementer training (i.e., brochure or workshop) to ensure proper implementation of the NMT program. Almost every program in the analysis included proper exercise instruction, exercise progression, and trainer or coach feedback. Importantly, programs that taught proper movement technique and knee stability during landing and other dynamic maneuvers during each training session were most effective. Surprisingly, some exercise components were found to be irrelevant (i.e., these programs were no more effective than those that did not include these exercise components), including balance, core strengthening, agility, and stretching. Although these components may be helpful in preventing other types of injuries (i.e., ankle sprains and muscle strains), they may be an ineffective use of time if the primary goal is ACL injury prevention. Some of these findings are consistent with those from other studies in the literature; for example, the prospective randomized intervention study by Söderman et al. which found no reduction in ACL injury in performing balancing exercises alone. However, Sugimoto et al. found a significant association in the reduction of ACL injury in programs that included core-strengthening/proximal control exercises. The authors discovered a recent trend for NMT programs to incorporate proximal control exercises, including plank, side plank, sit-ups/abdominal curl, push-ups, and upper body weight training. ^, There have been many laboratory-controlled studies that investigated the influence of proximal control on lower extremity muscle function and found associations among trunk, hip strength, and dynamic knee stability. ^, This finding is also consistent with the clinical practice guidelines that found level I evidence that female athletes, in particular, benefit from prevention programs that include trunk/core strengthening and stability exercises ( Fig. 5.2 ). Therefore incorporation of core strengthening and trunk stabilization appears to increase the effectiveness of ACL injury prevention programs.

Plank Exercise.

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