Fig. 24.1
Athletes should align knee over second and third toes to prevent dynamic valgus position
Fig. 24.2
(a, b) When landing, the trunk should lie within the base of support to improve stability. When the trunk is lateral to (a) or posterior to (b) the athlete’s base of support, noncontact ACL injuries are more likely
Force dissipation is the ability to absorb and adequately distribute forces when impacting the ground when running, landing, or cutting. In contrast force application is the ability to produce higher ground reaction forces to the ground when running, landing, or cutting. Being able to both absorb and apply more force to the ground improves sprinting performance [111–113]; however, these higher ground reaction forces, especially when experienced by those with reduced training age or experience [114], also increase an athlete’s risk of ACL injury during stop-jump tasks [68, 87, 89, 115]. Unfortunately, while training athletes to better dissipate ground reaction forces when landing does indeed work [79, 116, 117], it might actually worsen performance [118].
To address these contradicting goals, we recommend a two-step process when designing ACL injury prevention programs: (1) First learn to dissipate force by improving shock absorption through deceleration; (2) Learn to properly apply force to the ground when running, jumping/landing, and cutting. This approach can help athletes optimize force absorption when decelerating and enhance force generation performance needed for success in sports.
Strength of certain muscle groups must be adequately addressed when designing an ACL injury prevention program. While several muscles—like hip extensors, abdominals, and even those acting at the ankle—play a role in controlling lower extremity alignment and control, the primary muscle groups that play key roles in reducing the risk of ACL injury are the hamstrings, hip abductors, and quadriceps [33, 48, 50, 51, 74–76, 79–84]. As a review, Hamstrings help to reduce anterior tibial shear [119]; strength of this muscle group is well known in its ability to reduce ACL injury rate [48, 50, 51, 76, 79–84, 120]. Hip abductors and external rotators help to resist hip adduction, a primary component of the position associated with ACL injury, dynamic valgus [74]. The quadriceps are active eccentrically to dampen or control knee flexion. If insufficient quadriceps strength exists, it is likely that athletes will avoid knee flexion positions that rely on those muscles for control. The importance of quadriceps strength appears to be more of a factor for secondary or re-injury versus primary or initial ACL injury [121, 122].
The last component to consider when choosing the type of exercise is endurance, which includes both cardiovascular and muscular components. Establishing an adequate endurance base is an important part of reducing risk of ACL injury [90, 91, 93, 97, 123, 124].
There are several exercises that target the aforementioned variables and therefore may be used in an ACL injury prevention program. Table 24.1 provides a list of exercises that decrease an athlete’s risk of ACL tear. At the end of the chapter, a description and figure for each of these exercises is provided .
Table 24.1
Common ACL injury prevention exercises
Warm Up | Strength | Plyometric |
|---|---|---|
Skipping | Deadlift | Vertical Jump |
Walking Hamstring Stretch | Squat (Bilateral) | Squat Jump |
Ankle Hop | Squat (Single Leg) | Standing Long Jump |
Tuck Jump | Lunge—Forward and Lateral | Jump to Box |
Stability Hop—Front and Lateral | Step Up | Jump from Box |
RDL (Bilateral) | Single Leg Box Push-Off | |
RDL (Single Leg) | Vertical Jump (Single Leg) | |
Nordic Hamstring Curl | Standing Long Jump (Single Leg) | |
Knee Extension (Single Leg) | Jump over Object/Hurdle | |
Drop Jump (Bilateral) |
Exercise Technique Experience
Athlete training status and experience performing exercises is an essential part of exercise selection, especially for pediatric and adolescent female athletes [37, 38, 114]. Given their age and the need to improve movement quality, it is best to spend considerable time with each athlete to ensure that correct technique is used, even with those exercises that are relatively easy to perform. If the athlete uses incorrect technique, comprehensive, age-specific instruction should be provided to reduce aberrant movements that increase injury risk. The role of instruction to break the cycle of high risk movements is critical to avoid training the reinforces bad movement strategies [82, 125].
Equipment Availability
The availability of training equipment must be considered when choosing exercises for ACL injury prevention programs. Many such programs do not use equipment, primarily to make participation more convenient, with capacity to perform in conjunction with sport (e.g., soccer field, basketball court), and thereby improve compliance. For example, the depth (or drop) jump requires the use of a box to land from before jumping again (Fig. 24.3). The absence of plyometric boxes would therefore preclude this exercise. Or a single leg Romanian Deadlift might need to be substituted for a stability ball hamstring curl if a stability ball is unavailable. In most cases, ACL injury prevention programs can be implemented with little if any equipment as exercise selection and instruction can help overcome any limitations with available equipment.
Fig. 24.3
Equipment is often necessary when performing exercises to prevent ACL injury. Here, a 12 in. box is used during a depth (or drop) jump
Step Three: Training Load and Volume
Load most simply refers to the amount of weight assigned to an exercise and is one of the most critical aspects of an ACL injury prevention program. However, it must be noted that initially the complexity and novelty of some exercises may necessitate that no external resistance be used to allow the athlete to properly control the movement. As with any athlete beginning a training program, motor learning is an important initial occurrence prior to actual muscle fiber hypertrophy and strength. Bodyweight may initially provide sufficient demands during early participation in ACL injury prevention programs. Once technique has been mastered, either exercise complexity can be increased or external resistance can be added. To keep the stimulus to level needed for adaptive response the intensity—or load—of exercise must be progressed to avoid plateaus in strength and motor control development [126]. When training with sufficient load (>80% 1 repetition maximum), healthy individuals can increase strength [127, 128] and power within 3 to 6 weeks [129].
Exercise volume (dose) can be defined using a variety of equations. For our purposes, we will consider volume to be related only to the total number of repetitions performed during a workout session [130–132]. A set is defined as a group of repetitions performed sequentially before an athlete rests [130]. There is an inverse dose-response indicating that the higher the neuromuscular training volume, the greater the prophylactic effectiveness of the training program relative to increased benefit in ACL injury reduction among female athletes [96, 133]. A meta-analysis examining dose-response determined programs more than 30 minutes per session in duration demonstrated 26% lower risk of ACL injury compared to programs performed 15 min or less [95, 96]. Thirty minutes is a relatively short amount of time to perform exercise each week and should be deemed the minimum time spent on this activity [96].
Step Four: Training Frequency
Training frequency refers to the number of training sessions completed in a given time period, typically the number of training sessions per week. Program emphasis, and therefore training frequency, may vary depending on time within a training cycle. While there are several methods to divide a training cycle, we will focus on three distinct cycles, preseason, in-season, and off-season. Each cycle, or season, has a specific goal and with that goal, a recommended ACL injury prevention training frequency. While each season has importance it should be noted that programs that incorporate both preseason and in-season programming have the greatest positive impact on biomechanics and injury reduction [32, 134–136].
Preseason
The preseason is used to prepare the athlete for the upcoming competition season. The goal of the preseason is to maximize the athlete’s performance prior to competition. There is strong evidence that general preseason preparatory conditioning reduces overall injury risk. Likewise neuromuscular training implemented in as part of preseason conditioning is critical to alter high injury risk biomechanics and improve performance [49, 137–139]. In-season only ACL prevention strategies are limited in their potential to provide the adequate dosage and intensity to alter high risk biomechanics. Specifically, an intensive preseason ACL intervention reduced deficits points during the tuck jump assessment but no similar reductions were noted in an in-season only program [134–136]. These results are further supported by the data indicating that in-season only neuromuscular training program reduced ACL only in second half of season [32]. The concept of needed preseason ACL prevention is logical as it would not be expected prophylactic effect at the start of the season when risk is highest without adequate dosage that can be provided prior to initiation of competitive play.
In-season
In-season training scheduling presents logistical challenges such as limited practice time (NCAA restrictions) to dedicate to injury prevention versus sport skill development and training. Traditionally, three workouts per week are recommended by the majority of programs currently in place [43, 46, 57, 140], though some are performed five to six times per week by integrating into practice settings [34]. The loads and majority of these programs have athletes perform the assigned exercises before practices and/or games. With more experienced (intermediate or advanced) athletes, pre-practice or pre-game training can be augmented by using a split routine. Specifically, different muscle groups, movements, and exercises are trained on off days. Athletes training multiple times per week—as might occur as part of a sport-specific warm-up—demonstrated a 27% lower risk of ACL injury as compared to those training one time per week [133, 141].
Off-season
Often overlooked is what to do during the time athletes are not participating in formal practices or games. By definition, off-season lasts from the end of the season to the beginning of preseason. During these times, the authors advocate continuing to focus on alignment and technique while simultaneously training to improve muscular strength and endurance. Because preseason focuses so much on technique and alignment and in-season focuses on maintenance, off-season is when the majority of strength gains are made. Previously discussed was strength of the quadriceps, hamstrings, and hip abductors. Off-season is an ideal time to maximize the strength of those individual muscle groups while also using those muscles during more functional activities, like running and landing and jumping.
Step Five: Exercise Timing
In the context of ACL injury prevention , exercise timing refers to the placement of the assigned ACL injury prevention exercises when training. Although there are many ways to arrange exercises, decisions are invariably based on both convenience and how one exercise affects the quality of effort of other training sessions. Two primary approaches exist: performing the program combined with another training session (e.g., activity preparation/warm-up) or as a standalone training program.
Most ACL injury programs are performed in combination with other training sessions, specifically prior to practice or games, and have been shown to increase compliance [59]. Fatigue is a risk factor of ACL injury [90, 91, 93–98], therefore, performing exercises right after other training sessions is another option to consider. Learning and understanding how to properly move and land when fatigued is an important component of injury prevention and might be an option when considering the timing of ACL injury prevention programming. Therefore, while it should not be every session, purposeful performance of an ACL injury prevention program after other training sessions is recommended.
Another option is incorporating ACL injury prevention as a standalone program, especially during the off-season. Doing this will allow the athlete to better address strength and endurance at levels that are more conducive to the sought after gains [126]. Ultimately the most critical factor related to timing is when the season and schedule allow to get the best quantity and quality dosage of exercise targeted to reduce ACL injury risk factors [59, 96, 133, 141].
Conclusion
Well-designed ACL injury prevention programs are based on determined risk factors for injury and application of program design principles to minimize risk. Once those exercises are chosen, selecting the load and volume of those exercises is considered next. Finally, the training frequency, exercise order, and timing are done. Table 24.2 provides a sample program to reduce ACL injury risk.
Table 24.2
Putting it all together: Sample Program
Preseason | In-Season | Off-season |
|---|---|---|
Two parts | ||
GOAL To prepare the athlete for the upcoming competition season by using sport-and movement-specific exercises | GOAL To maintain the strength and movement quality developed during the preseason | GOAL To increase strength and power while continuing to focus on proper movement quality |
EXERCISES Deadlift Stability Hop Single Leg RDL Standing Long Jump Single Leg Squat Drop Jump Nordic Hamstring Curl | EXERCISES Stability Hop Single Leg RDL Standing Long Jump Single Leg Squat Drop Jump | EXERCISES—Plyometric (Choose 4 for Part I, Choose other 4 for Part II) Jump to Box Jump From Box Squat Jump Single Leg Push Off Standing Long Jump (SL) Vertical Jump (SL) Jump Over Object/Hurdle Drop Jump |
EXERCISES—Strength (Choose 4 for Part I, Choose other 4 for Part II) Deadlift Double Leg Squat Single Leg Squat Double Leg RDL Nordic Hamstring Curl Lunge—Forward Lunge—Lateral Step Up | ||
FREQUENCY 3×/week | FREQUENCY 2×/week | FREQUENCY 4×/week |
SETS PER EXERCISE 3 | SETS PER EXERCISE 2 | SETS PER EXERCISE 4 |
REPETITIONS PER SET 10 | REPETITIONS PER SET 8 | REPETITIONS PER SET 8–15 (Depending on the Off-season phase) |
Appendix:
- 1.
Warm Up Exercises
Skipping
Preparatory position
Athlete lifts leg to approximately 90° of hip and knee flexion.
Step One
Athlete jumps up and forward on one leg. Athlete’s opposite leg should remain in the starting flexed position until landing. As one leg is lifted, athlete lifts opposite arm.
Step Two
Athlete lands on the same leg and immediately repeats the skip on the other side.
Alignment Cues
Knees should not move inward (dynamic valgus)
.
Walking Hamstring Stretch
Preparatory Position
Athlete assumes a comfortable, standing position with feet shoulder- to hip-width apart.
Step One
Athlete lowers torso by flexing the hips and lifts opposite leg backward while maintaining neutral lumbar alignment.
Athlete holds stretch position for one second, then steps backward while stretching.
Step Two
Athlete returns to preparatory position by extending the hips.
Note: This exercise can also be performed with a barbell or two dumbbells for resistance. With a barbell, the position described with the deadlift exercise is used and care must be used to ensure bar remains close to the athlete’s thighs. With dumbbells, the dumbbells to hang at arm’s length in front of the body throughout the exercise.
Alignment Cues
Knees should not move inward (dynamic valgus).
Ankle Hop
Preparatory position
Athlete assumes a comfortable, standing position with feet shoulder- to hip-width apart.
Step One
Athlete hops up, with most of the motion occurring at the ankle joint.
Step Two
Athlete lands and immediately repeats the hop.
Alignment Cues
Minimal horizontal or lateral movement should occur.
Knees should not move inward (dynamic valgus).
Tuck Jump
Preparatory position
Athlete assumes a comfortable, standing position with feet shoulder- to hip-width apart.
Step One
Athlete jumps up and pulls the knees to the chest. Athlete quickly grasps the knees with hands, and then releases.
Step Two
Athlete lands and immediately repeats the tuck jump.
Alignment Cues
Minimal horizontal or lateral movement should occur.
Knees should not move inward (dynamic valgus).
Stability Hop—Front and Lateral
Preparatory position
Athlete assumes a comfortable, standing position on one foot. The athlete holds the non-jumping leg in a stationary position with the knee flexed.
Step One
Athlete performs a countermovement and explosively jumps forward and up; athlete may use both arms to assist.
Step Two
Athlete lands on the opposite leg and repeats the jump.
Note: Athlete should briefly recover between jumps (i.e., speed between jumps is not the focus).
Note: This may also be performed to the side.
Alignment Cues
Knee should not move inward (dynamic valgus).
- 2.
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Strength Exercises
Deadlift
Preparatory Position
Athlete assumes a comfortable, standing position with feet shoulder- to hip-width apart.
Athlete squats down and grasps the bar with a closed, pronated grip. Athlete places hands on the bar slightly wider than shoulder-width apart with the arms outside the knees and elbows fully extended.
Athlete places positions the bar approximately 1 inch in front of the shins.
Athlete positions the body with the back flat, chest held up, head in line with the spine, weight balanced between the balls and heels of the feet; athlete looks straight ahead.
Step One
Athlete lifts the bar off the floor by extending the hips and knees.
Athlete maintains a flat-back position with elbows fully extended.
Athlete keeps the bar as close to the shins as possible.
Athlete moves the hips forward as the bar rises just above the knees.
Athlete continues until the body is fully erect.
Step Two
Athlete flexes the hips and knees to slowly lower the bar to the floor.
Athlete maintains a flat-back position with elbows fully extended.
Alignment Cues
Knees should not move inward (dynamic valgus).
Lumbar lordosis should remain.
Bar should not move too far forward.
Elbows should remain extended
.
Squat (Bilateral)
Preparatory Position
Athlete grasps the bar with a closed, pronated grip and steps under the bar and position the feet parallel to each other.
Athlete place the bar across the posterior deltoids and positions the body with chest held up, looking straight ahead.
Position the feet shoulder- to hip-width apart.
Step One
Athlete maintains a position with the back flat and the chest up.
Athlete lowers body by flexing the hips and knees while maintaining a flat-back position, the heels on the floor, and the knees lined up over the second and third toes.
Athlete continues lowering until one of the following occurs:
The thighs are parallel to the floor.
The trunk begins to round forward.
The heels rise off the floor.
The knees move out of alignment.
Step Two
Athlete maintains a position with the back flat and the chest up.
Athlete extends the hips and knees at the same rate with the heels on the floor and the knees properly aligned until the body is fully erect.
Alignment Cues
Knees should not move inward (dynamic valgus).
Lumbar lordosis should remain.
Knees should not move forward past the athlete’s feet
.
Squat (Single Leg)
Preparatory Position
Athlete assumes a comfortable, standing position on one foot. The athlete places the other leg in a stationary position either in front or to the back on a bench.
Step One
Athlete maintains a position with the back flat and the chest up.
Athlete lowers body by flexing the hips and knees while maintaining a flat-back position, the heel on the floor, and the knee lined up over the second and third toes.
Athlete continues lowering until one of the following occurs:
The thighs are parallel to the floor.
The trunk begins to round forward.
The heels rise off the floor.
The knees move out of alignment.
Step Two
Athlete maintains a position with the back flat and the chest up.
Athlete extends the hip and knee at the same rate with the heel on the floor and the knee properly aligned until the body is fully erect.
Alignment Cues
Knee should not move inward (dynamic valgus).
Lumbar lordosis should remain.
Knee should not move forward past the athlete’s feet.
Pelvis should remain level.
Lunge—Forward and Lateral
Preparatory Position
Athlete assumes a comfortable, standing position with feet shoulder- to hip-width apart.
Step One
Athlete maintains a position with the back flat and the chest up.
Athlete takes one big step forward with the lead leg.
Athlete keeps the trailing foot in the starting position with the trailing knee slightly flexing.
Athlete plants the lead foot on the floor with the lead knee lined up over the second and third toes.
Athlete continues to lower the body until the trailing knee is 1–2 in. above the floor (trailing knee is not to contact the floor).
Step Two
Athlete maintains a position with the back flat and the chest up and forcefully pushes off the floor with the lead leg until the lead foot is next to the trailing foot.
Note: This exercise can also be performed with a barbell or two dumbbells for resistance. With a barbell, the position described with the squat exercise is used. With dumbbells, the dumbbells to hang at arm’s length alongside the body throughout the exercise.
Note: This exercise can also be performed laterally by taking a big step to the side instead of forward during Step One.
Alignment Cues
Knees should not move inward (dynamic valgus).
Lumbar lordosis should remain.
Knees should not move forward past the athlete’s feet.
Step Up
Preparatory Position
Athlete assumes a comfortable, standing position with feet shoulder- to hip-width apart in front of a box.
Step One
Athlete step up onto the box with the lead leg and places the entire foot on the top of the box.
Athlete maintains a position with the back flat and the chest up.
Athlete extends the lead hip and knee to move the trailing leg and body to a standing position on top of the box.
Athlete minimizes push off or hop up with the trailing leg or foot.
Step Two
Athlete step off the box with the same trailing leg. Athlete maintains a position with the back flat and the chest up.
Athlete places the trailing foot on the floor approximately 12 in. from the box.
Athlete shifts the body weight to the trailing leg when the trailing foot is in full contact with the floor.
Athlete steps off the box with the lead leg and brings the lead foot back to a position next to the trailing foot.
Note: The box used should be 12–18 in. high so that a 90° knee angle occurs when the foot is on the box.
Note: This exercise can also be performed with a barbell or two dumbbells for resistance. With a barbell, the position described with the squat exercise is used. With dumbbells, the dumbbells to hang at arm’s length alongside the body throughout the exercise.
Alignment Cues
Knees should not move inward (dynamic valgus).
RDL (Bilateral)
Preparatory Position
Athlete assumes a comfortable, standing position with feet shoulder- to hip-width apart.
Step One
Athlete flexes the knees to approximately 30° and keeps them in this position throughout this exercise.
Athlete lowers torso by flexing the hips and moving them backward while maintaining neutral lumbar alignment.
Athlete continues lowering until hands are level with bilateral patellar tendons or until moving lower changes lumbar position.
Step Two
Athlete returns to preparatory position by extending the hips.
Note: This exercise can also be performed with a barbell or two dumbbells for resistance. With a barbell, the position described with the deadlift exercise is used and care must be used to ensure bar remains close to the athlete’s thighs. With dumbbells, the dumbbells to hang at arm’s length in front of the body throughout the exercise.
Alignment Cues
Knees should not move inward (dynamic valgus).
Knees should not flex more than 30°.
Lumbar lordosis should remain
.
RDL (Single Leg)
Preparatory Position
Athlete assumes a comfortable, standing position on one foot. The athlete holds the non-exercising leg off the floor and it remains off the floor during the exercise.
Step One
Athlete flexes the knee of the exercising limb to approximately 30° and keeps them in this position throughout this exercise.
Athlete lowers torso by flexing the hips and moving them backward while maintaining neutral lumbar alignment.
Athlete continues lowering until hands are level with bilateral patellar tendons or until moving lower changes lumbar position.
Athlete allows non-exercising leg to move backward/posteriorly during this initial step.
Step Two
Athlete returns to preparatory position by extending the hips of the exercising leg and allowing the non-exercising leg to return to a position next to the exercising leg.
Note: This exercise can also be performed with a barbell, two dumbbells, or a kettlebell for resistance. With a barbell, the position described with the deadlift exercise is used and care must be used to ensure bar remains close to the athlete’s thighs. With dumbbells, the dumbbells to hang at arm’s length in front of the body throughout the exercise. With kettlebell, the athlete typically grasps the kettlebell in the contralateral hand.Related posts:
Partial ACL Injuries in Pediatric and Adolescent Athletes
Surgical Considerations and Treatment Algorithm for ACL Tear
New Horizons in ACL Surgery
Review of Different Surgical Techniques for All-Epiphyseal Anterior Cruciate Ligament Reconstruction
ACL Reconstruction Using Epiphyseal Tunnels
Rehabilitation and Return to Sports After Anterior Cruciate Ligament Reconstruction in the Young Athlete
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