Anterior cruciate ligament (ACL) injuries are one of the most common and devastating knee injuries sustained while participating in sport. ACL reconstruction (ACLR) remains the standard approach for athletes who aim to return to high-level sporting activities. Less than half of the athletes who undergo ACLR are able to return to sport within the first year after surgery (2); on return, around 25% of these athletes will have a subsequent second ACL injury (11,13), with the outcomes from second surgery being considerably worse (23). Not only do these athletes have a 1 in 4 chance of reinjuring an ACL but they also have a 1 in 2 chance of developing significantly clinical and radiological osteoarthritis of both the tibiofemoral and patellofemoral joints within 10–15 years (21). Female athletes fair far worse with at least a 3 times greater risk than male counterparts with injury rates in full-time athletes at around 5% (22). With all these issues in mind, considerable emphasis has been placed on the prevention of ACL injuries.
A valgus or abducted position of the knee on landing and during cutting has been associated with these ACL injuries (3,10,18), with this movement pattern being particularly common in female athletes (5,6). The poor neuromuscular control associated with the above movement pattern has been regarded as a potentially modifiable risk factor, which could become the target of an injury prevention program. Jump-training programs have been reported within the literature to improve both landing knee valgus (3,8,9) and functional performance (8,12). Jump-training programs have also been shown to reduce ACL injury rates in female athletes (9,15,19). Despite these notable successes, ACL injury rates still seem to be rising (1,2) and compliance and take up of these programs are far from universal. Possible reasons why the occurrence is rising are likely to be multifactorial, but factors, such as adherence to intervention programs (24) and transference of learning to sporting environments, are likely to be significant (16)
The majority of the jump-training programs reported in the literature have been of minimum of 6–8 weeks duration, performed 3 times per week, with sessions often lasting from 30 minutes to 1 hour in duration (24). For most sports coaches, team conditioners, and athletes, these duration and program length are not acceptable. Furthermore, the majority of the jump-training programs reported in the literature incorporate a variety of training elements alongside the jump training (9,12,20), and it remains unclear if it is jump training that makes the difference or a combined strength, flexibility, and jump-training program. Only one study to date has looked at the impact of a single element (jump training) and found positive benefits on neuromuscular control (8). The short duration (15 minutes) of the sessions is likely to have an impact both on adherence and on long-term incorporation of the programs into athletic conditioning.
The transference of the ability to execute an appropriate landing strategy into the sporting context is also likely to be a contributing factor. The majority of neuromuscular training studies have used tests to monitor performance, which are very similar to the exercises in the training program and therefore are essentially training to pass the test. A number of studies have shown providing immediate verbal and visual feedback can significantly improve performance (7,17). This questions the true significance of the changes found, as similar results have been achieved with immediate verbal and visual feedback as jump-training programs. Only a limited number of studies have followed up the training interventions for changes in movement practices in the medium or long term (3,4), and therefore, the level of retention of this improved lower limb control has not yet clearly been demonstrated.
There are no current studies that have assessed the transference of appropriate landing and cutting strategies into sport-specific skills. Current training practices have a reliance on closed skill activities carried out in a block order (16); typically, this involves repeated practices of the closed skill (same movement tasks in stable predictable environments most often carried out at a pace defined by the participant). To more appropriately reflect the motor skill requirements of sports, especially team sports, the programs need to have progressively increasing complexity where more open-skill (nonplanned skills/tasks) elements become incorporated in a more and more random fashion once the closed skill tasks have been mastered (25). This leads to practices that are initially controlled and self-paced, allowing the participant to understand and learn the specifics of the appropriate movement patterns in environments that are predictable and static to allow them to plan their movements in advance (closed skill practice). The practices would then need to progress to incorporate more random elements, where the environment is unpredictable and changing and the performer needs to adapt their movements in response (open-skill practice).
The aim of this article is to introduce a progressive jump-training program that can be incorporated into a warm-up or as a stand-alone session and develops the participants' landing skills through progressively more challenging tasks. This hopefully will progress the idea and the program presented previously in this journal (14) while further developing the ideas of another article previously presented in this journal (16). The program moves progressively through an initial phase that involves discrete closed movements in a block practice format, an intermediate phase that incorporates a combination of some closed and controlled open-skill elements, and finally practice elements that involve open movements in a random practice format.
APPROPRIATE LANDING STRATEGY
The correct landing technique should be encouraged at all times (8,18). The participant should aim to have a relatively upright torso that does not lean or sway in any direction on landing with arms that are not fixed or clamping down onto the body for stability. The pelvis should stay in level with the frontal (no lateral tilt) and sagittal (no excessive anterior tilt) planes. The hip should flex greater than 45° and not drop into adduction or internal rotation. The knee should flex greater than 60° and not drop in an adducted position (knee pointing in toward first toe or beyond) (Figure 1). The landing should be held for 3 seconds with minimal body movement (8,9,17,18). Coaching staff (or teammates, if staffing is limited) should provide a real-time feedback regarding landing strategy, especially in the early stages of the program while the athlete is learning this discrete skill within the closed skill practice phase.
CLOSED SKILL BLOCK PRACTICE PHASE
This initial phase involves the repeated practice of discrete movements with the emphasis on correct limb alignment. These are practiced in brief and well-defined blocks of predictable (known) movement sequences. The initial closed skill block practice element is based on the truncated jump-landing program of Herrington (8). This program was 15 minutes in duration, undertaken 3 times per week, incorporating progressively more difficult jump landings, in terms of directional control and the progression from bilateral to unilateral landings. The program (Figure 2) generated significant improvements in knee valgus angle during both drop jump landings and basketball jump shots and crossover hop distance (8).
The combination phase is an intermediate phase where some random elements are incorporated in the practice of the jump landings, but these are still with clearly defined sequences or activities. In the combination phase, the athlete carries out the closed skill task but with a reaction-based element from verbal cues for instance. The incorporation of more random elements when undertaking either bilateral or unilateral jumping or landing would involve the coach giving a verbal command to which the athlete responds. For instance, it could involve jumping and landing to the left or right, or forward or backward in response to a verbal cue. This could be progressed to incorporate jumps with 90 or 180° rotations or hops rotating clockwise or counterclockwise, with the elements or degree of rotation and direction being randomly verbally cued (either by a member of the coaching staff or by another athlete). Jumping or hopping and landing off a series of boxes of different heights in combinations of forward, sideways, or backward initially after a sequence and then with direction-specific verbal cues would be another example (Figure 3).
OPEN-SKILL RANDOM PRACTICE PHASE
In this phase, the environment the athlete is now performing in is unpredictable in terms of the task to be undertaken, the number of times, and the order, in an attempt to develop and execute appropriate landing skills in a chaotic environment that more reflects the sporting one. Incorporating many of the activities above can be integrated with random elements such as catching a ball, heading a ball, bungee cords, and opposition shadowing. The exercises from the combination phase can be repeated with a sport-specific task such as catching a ball during the flight phase, or heading a ball during the flight phase. Utilizing a partner or multiple partners increases the randomness because of the variability of the direction from which the ball comes. The exercises of the combination phase can be repeated, with the participant having a bungee cord around their waist, a partner-coach pulls the cord during the flight phase to provide perturbation to the landing. Working with partners, the participants have to shadow the movements of their partner; this can also incorporate passes to each other at the same time (Figure 4). During these tasks, specific feedback regarding lower limb alignment during the tasks should be provided to the athlete(s) by the strength and conditioning and sports medicine staff.
INTEGRATION AND IMPLEMENTATION
During preseason training, these injury prevention programs can be performed independent of the rest of the athletes' training or incorporated as filler exercises during the rest period between sets. In season, injury prevention exercises can be integrated into the athletes' warm-up procedures, before both training (on the field or in the weight room) and competition, to prevent any substantial increases in total training volume. It is essential that during the performances of these tasks that athletes receive feedback regarding their landing strategy, from coaching staff or from each other (which may aid their learning/understanding of the appropriate landing strategy), to ensure an appropriate landing strategy.
ACL injury is a major problem for the athlete in terms of not only the rehabilitation period required after surgery and the subsequent time away from the sport but also because of the high risk of injury reoccurrence and other comorbidities, such as osteoarthritis. Patients after ACL surgery also have a poor outcome related to the level of competitive sport they are able to sustain. These factors have led to the development of ACL injury prevention programs. These have had some success but despite this have not been universally implemented. One reason for this may be the nature of the programs themselves, which are based around closed skill activities that potentially limited transference into performance of sports-related tasks. This article has discussed incorporating progressively more open-skill random activities into jump-training activities that while still incorporating and allowing for practice of fundamental correct limb alignment control on landing, do that in an increasing more taxing environment to hopefully aid skill transference into sports performance.
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Keywords:© 2013 by the National Strength & Conditioning Association
anterior cruciate ligament; injury prevention; motor learning; integration