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Int J Sports Phys Ther
Int J Sports Phys Ther
2159
International Journal of Sports Physical Therapy
2159-2896
NASMI Website: International Journal of Sports Physical Therapy

34123540
23549
10.26603/001c.23549
Clinical Commentary/Current Concept Review
Recommendations for Plyometric Training after ACL Reconstruction – A Clinical Commentary
Buckthorpe Matthew PhD 1
Della Villa Francesco MD 2
1 Education & Research Department, Isokinetic Medical Group, FIFA Medical Centre of Excellence, Bologna, Italy; Faculty of Sport, Health and Applied Science, St Marys University, London, UK
2 Education & Research Department, Isokinetic Medical Group, FIFA Medical Centre of Excellence, Bologna, Italy
Corresponding author: Matthew Buckthorpe Faculty of Sport, Health and Applied Science, St Marys University, Twickenham, London, UK TW1 4SX Email: matthew.buckthorpe@stmarys.ac.uk
1 6 2021
2021
16 3 879895
24 2 2020
30 12 2020
© The Author(s)
https://creativecommons.org/licenses/by-nc-sa/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike License (4.0) which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited. If you remix, transform, or build upon this work, you must distribute your contributions under the same license as the original.

This paper presents a four-stage plyometric program to be undertaken as part of criterion-based rehabilitation for athletes with anterior cruciate ligament reconstruction (ACLR). After ACLR, the patient experiences alterations of joint mobility, gait and movement patterns, neuromuscular function and general physical fitness. Plyometric training is an important component for neuromuscular and movement re-conditioning after ACLR. Effective use of plyometrics can support enhancements in explosive sporting performance, movement quality and lower risk of injury. Plyometric training, as a component of the ACL functional recovery process, can aid in restoring function and supporting timely return to sport. However, few patients undertake or complete a plyometric program prior to return-to-sport. To truly impact individual patients, a stronger focus on research implementation is needed from researchers to translate efficacious interventions into practice. In designing a plyometric program, it is important to match the specific plyometric tasks to the functional recovery status of the ACLR patient. To do this, it is important to understand the relative intensity of plyometrics tasks, align these tasks to the ACL functional recovery process and monitor the athlete as part of criterion based rehabilitation. Plyometric intensity is based on the intensity of efforts, the vertical and/or horizontal momentum prior to ground contact, the ground contact time and the surface or environment on which they are performed on/in. Furthermore, how the person technically performs the task will influence joint loading. There should be a gradual increase in task intensity and specificity throughout the program, with all tasks used for both neuromuscular and motor control re-conditioning. The aim of this paper is to provide recommendations to clinicians on how to design and implement plyometric training programs for the ACLR patient, as part of the functional recovery process.

Level of evidence

5

rehabilitation
reconditioning
neuromuscular performance
movement performance
injury prevention
==== Body
pmcINTRODUCTION

A key goal within sports medicine is to improve the outcomes of patients after major injury. It appears that many patients fail to return-to-sport (RTS) and/or previous sporting performance levels after anterior cruciate ligament reconstruction (ACLR).1–4 Those who RTS, do so often at much elevated risk of re-injury, with typically around nearly one in three young athletes experiencing a knee re-injury,5,6 generally within the first two years after RTS.7 Current opinion is that in order to improve athlete outcomes after ACLR, there is a need to optimize the processes and practices of rehabilitation.8,9 Key areas suggested in need of improvement are the restoration of neuromuscular performance (e.g., strength and power) and movement quality of patients prior to RTS after ACLR.8–11 Following ACLR, at the time of RTS, patients often present with deficits in knee extensor maximal strength12–14 and rate of force development (RFD),15,16 as well as lower limb/closed chain strength15 and power.17 Furthermore, patients often RTS with movement asymmetries during an array of functional tasks18–23 thought to predispose them to increased risk of injury.7,24–26

One highly valued element of rehabilitation after ACLR is the use of plyometric training.8 Plyometric exercises involve a stretch-shortening cycle, which is a commonly observed phenomenon involving a rapid lengthening of a muscle tendon unit, immediately followed by a rapid shortening (for a review see Davies et al.).27 Plyometric training has long been used to optimize explosive sporting performance (e.g., speed, jump height) of athletes and is regarded as an excellent training method, due to the wide ranging neuromuscular and motor control benefits.28–32 In particular, plyometric training has been reported to be superior to more traditional resistance training for development of explosive lower limb performance (power/RFD),30,31,33 as well as effective at eliciting gains in maximal strength,32 and sports performance variables, such as linear34 and multiple directional29 movement speeds.

Ebert et al.35 reported that only 30% of patients completed a plyometric program prior to RTS after ACLR.35 A key issue with implementing plyometric training into the functional recovery process of ACLR patients is a lack of guidance within the literature on how and when to do it. Plyometric tasks vary in their intensity and specificity, with typical peak ground reaction forces (GRF) ranging from 1.5-7 times body mass.36–40 Inappropriate plyometric task choice could thus be expected to cause adverse reactions on an unprepared person after major lower limb injury. There is a need to support practitioners on how to effectively use plyometrics after major lower limb injury, such as ACLR. To do this, there is a need to understand the types of plyometrics available, their relative loading/intensity and understand how to systematically incorporate plyometric training as part of the ACL functional recovery pathway. Therefore, the aim of this paper is to provide recommendations to clinicians on how to design and implement plyometric training programs for the ACLR patient, as part of the functional recovery process. This will hopefully aid a reduction in the barriers between research and effective implementation into practice.

PLYOMETRIC TRAINING AFTER ACL RECONSTRUCTION – KEY CONSIDERATIONS IN PROGRAM DESIGN

Designing a plyometric training program to develop neuromuscular performance and movement quality, while respecting tissue healing, is an important consideration for the rehabilitation specialist.9,41 In planning effective plyometric use and progressions, it is important to have consideration of optimal loading (defined as the load applied to structures that maximizes physiological adaptation)41 to bring about specific neural, morphological and mechanical adaptations.41 Optimal plyometric program design entails an understanding of the specific loading demands of the various plyometric tasks, so a series of optimal progressions can be planned. It is important to consider the intensity of movement or the specific external and internal loading of the task(s). External forces are the result of equal and opposite forces acting on the body according to the laws of motion (e.g., Newton’s laws), while the internal joint loads will depend on how the GFR loads are distributed throughout the body. Load is actively accepted/dissipated via the neuromuscular system and absorbed passively via the tendons, ligaments and joints during movements. Internal hip-, knee-, and ankle-extension (plantarflexion) moments must be produced via eccentric, isometric and concentric muscle contractions to control joint motion, absorb the kinetic energy of the body at impact and produce force and power to propel the body ballistically during plyometric tasks.42 Inability to accept load either due to deficits in strength, would mean a greater reliance on joint complexes (tendon, ligament and joint structures) for passive force absorption.43 It is important to understand the specific loading demands of the various tasks, the patients capacity to tolerate these loading demands (e.g., strength and movement quality) and understand how the patient has responded to the specific loads on an individual level (e.g., monitoring loading response).

Plyometric task intensity and complexity

In terms of plyometric loading, it is important to consider the peak external loads of the tasks, the joint specific internal moments, the neuromuscular activation/muscle forces as well as the neuromuscular control challenge. In addition, consideration of volume load is important.

During movement, an individual must produce and accept force via its application to the ground according Newtons laws of motion. Newtons third law dictates that there will be an equal and opposite reaction, whilst Newtons second law, the law of acceleration, dictates movement acceleration will be a product of force application relative to body mass (Force = mass x acceleration). Intensity of plyometric tasks can be considered on the basis of peak GRFs, which typically occur during the eccentric/landing phase, but also peak concentric forces (and power) are important on a performance level. In addition, the rate of force acceptance and development is important. This is essentially the rate of change in force during the landing and jumping phases of a plyometric task.

Peak external loading is largely dictated by task selection, the neuromuscular capacity to accept and develop force (e.g., strength), surface/environment and ground contact time (GCT)/instruction:

59304 Table 1: The four types of plyometric task based on stance position at landing and/or take-off, with description and examples.

Plyometric type	Description	Example(s)	
Unilateral	Involve eccentrically accepting load on one limb and then concentrically developing force and power to accelerate again on one limb. This includes jumping from one limb to the other (e.g., bounding/ running), or continuous same limb plyometrics (e.g., hops).	Bounding (alternating bounds, speed bounds, bounds for height etc.); SL SJ, SL CMJ, SL drop jump; lateral jumping and hopping; rotational hopping/ jumping	
Bilateral (symmetrical)	Both limbs accept and produce force simultaneously from a symmetrical stance position	BL SJ, BL CMJ, BL drop jump; tuck jump	
Bilateral (asymmetrical)	Both feet take off and/or contact the ground simultaneously but in different positions. As such, the demand placed on each leg is different and shared.	Split jumps, same stance landing, alternating leg position	
Bilateral (with timing off-set)	Typically involve landing on one limb before taking off on the other limb. These exercises can be defined as skipping type movements and do not characterize the typical stretch shortening cycle motion on a single limb.	Skipping Alternating box split jumps	

Task selection: Plyometric tasks can be considered based on stance and body positioning at take-off/landing, consisting of unilateral and different bilateral versions (Table 1 and Figure 1). During the eccentric phase of a plyometric task, the athlete will need to decelerate the center of mass, prior to producing force and power to ballistically propel oneself as part of the plyometric action. The peak eccentric forces will largely be dictated via the velocity or the relative momentum of the system, as a whole at impact/landing.40 The higher the momentum (mass x velocity) prior to/ at impact, the greater the eccentric work required to decelerate the body. As such, intensity of effort and height of landing and/or horizontal speed prior to deceleration are major determinants of peak loading of plyometric tasks.

59305 Figure 1: Four types of plyometrics, A) bilateral off-set (alternating box jump), B) bilateral asymmetrical (split jump), c) bilateral symmetrical (30 cm drop jump) and d) unilateral (30 cm drop jump

Strength: greater total lower extremity energy absorption in the sagittal plane has been associated with smaller vertical GRF and greater knee-flexion displacements during landing.44,45

Surface: a compliant surface will deform under load and as such joint loading is influenced by the surface stiffness. Performing plyometrics in water or on sand has been shown to reduce the high impacts and results in less muscle soreness than performing plyometrics on more rigid surfaces.46 For example, at the appropriate depth of water in the pool, there appears to be a reduction of around 45-60% in peak GRFs recorded from plyometric exercise in water versus on land.39,47

GCT: peak force and particularly RFD and rate of power development will also be dictated by GCT. The RFD and rate of power development will be a function of force/power produced divided by the GCT, derived as the reactive strength index. GCT and associated RFD are influenced by task choice but also instructions given for performance of the task (e.g., land and jump leaving the ground as quickly as possible).40 GCT (and associated RFD and neural activation during the task) are important considerations in terms of specificity of training adaptations. Improvements in explosive neuromuscular performance appear to be specific to the GCT,29 with longer GCT (>250-500 ms) suited to acceleration and multidirectional movement performance, whilst linear based (horizontal and vertical) fast (GCT < 200 ms) plyometrics may be better suited for developing linear peak running speeds.

As well as peak external loading, it is also important to consider the relative internal joint loading and associated neuromuscular activation and muscle forces. Internal joint loads should be considered across three planes of motion (sagittal, frontal and transverse). During functional tasks, there is a load sharing across joints and muscle groups.48 The relative ‘torque’ experienced at each joint and subsequent muscle forces will be a product of the resultant GRF and the respective distance away from the joint (torque = force x distance). The specific joint loading will be influenced by task selection,40 and kinematics during the task. For example, altering the trunk alignment during plyometric exercise would alter the center of mass and position it closer or further away from the joint.49 A more upright and stiff posture, described as a quadriceps dominant behavior,50 has been correlated with higher knee-extensor moments.51 Greater hip flexion to knee flexion ratios during plyometric type tasks has been shown to reduce knee-extensor moment and knee energy absorption52,53 and increase hip loading.49 Altered frontal- and transverse-plane knee loading has been shown to contribute to greater ACL loading.54–57 It is recommended to avoid at risk movement biomechanics, specifically a knee dominant motor strategy (e.g., upright trunk positioning) in conjunction with altered frontal (hip and tibial abduction) and transverse plane (tibial rotations and/or internal hip rotation) motions during plyometric tasks, as these will exacerbate knee and ACL loading.54–57

It is also important to consider the relative neuromuscular control challenge/loading, when prescribing plyometric progressions. It is thought that effective use of plyometrics can support improved movement quality and reduce ACL injury risk.31,32,58–60 It is known that strength training does not directly improve movement quality during sport-type movements.61 Instead, there is a need to incorporate more sport type movements to relearn and improve movement coordination during sport-type tasks.62 Plyometric drills can improve neuromuscular control in athletes, which can become a learned skill that transfers to sporting competitive movements,31 aiding in the restoration of sport-specific movement quality after injury. For optimal motor learning (defined as ’the process of an individual’s ability to acquire motor skills with a relatively permanent change in performance as a function of practice or experience),63 it is important that the tasks are performed repeatedly with good movement quality.64,65 Thus, it is important to provide the right challenge to neuromuscular control, with progressive increases in movement complexity, as well as rate and intensity of loading.66

While considering the specific loading of a singular task or repetition is important, as discussed, it is also important to consider the volume of loading. Volume load is the result of many actions during a session or over time (e.g. day/week/month). It is known that high recurrent loading of the ACL can lead to graft creeping and eventually failure.67 Furthermore, issues such as patellofemoral pain syndrome are typically the cumulation of chronic overload68 and common after ACLR.69–71 It is recommended to monitor the cumulative loading of respective tasks, which can be done through documenting the exercise sets/foot contacts alongside the task intensity.

Are they strong enough?

It is well accepted that sufficient strength of the lower limb(s) is important for implementation of plyometrics.72–75 Inability to accept load would mean a greater reliance on joint complexes (tendon, ligament and joint structures) for passive force absorption.43 Considering the various descriptors of load, it would seem appropriate to have an understanding of the patients ability for compound muscle strength, to be able to tolerate the external ground reaction forces. Assessing and tracking closed chain strength (e.g., squat and/or leg press strength) can support optimal task progressions.8,9,76 It is important that the plyometric tasks are aligned to the strength status of the athlete and that task intensity supports and tracks with improvements in strength and functionality. The assessment of closed chain strength (e.g., leg press/squat strength) has been suggested to determine the readiness for the introduction of running on treadmill (e.g., 1.25 times body mass single leg press),9,76 unilateral plyometrics (1.5 times body mass single leg press)8,76 and RTS (2 times body mass single leg press).8,76

Additionally, it is important to understand each joint’s ability to withstand loads. The ankle, knee and hip/trunk must accept and produce force in a load sharing manner,48 depending upon the task and the specific movement quality of the patient. Knee extensor strength is a major barrier to functional progressions after ACLR77 and so understanding the knee extensors strength of the ACLR athlete is important to implement and progress plyometric tasks. Patients will typically display large deficits in knee extensor strength in the early weeks after surgery (e.g., 50% deficits at four weeks post ACLR).78 Restoring knee extensor strength is essential to allow for movement based retraining and implementation of plyometrics.9,79 Assessing knee extensor strength using concentric or isometric assessment of the isokinetic dynamometer or recording knee extension loads used in rehabilitation (eg, 8 or 10 repetition maximum) can provide indication of knee extensor strength to support plyometric implementation and progressions. Knee extensor limb symmetry index (LSI) is often used to support progression through stages of an ACLR rehabilitation pathway.8,9 It can be used to support decision making of when patients are ready to perform certain functional tasks including jogging on the treadmill (LSI, 0.70),9,76,80 single leg landing and jumping drills (LSI, 0.80),8,9,76 RTS training (LSI, 0.90)8,76 and return to high level competitive sport (LSI, 1.0).8,80

Do they move well enough?

As well as aligning plyometric loading to strength, it is also important to align plyometric task complexity to movement capabilities. So, it would appear important to know if an athlete is able to perform the task sufficiently well and safely prior to training prescription. Furthermore, it is important to monitor movement quality during the task. This would aid in ensuring that the athlete performs the task with appropriate kinematics before progressing to a subsequently harder task (either higher loading or greater movement complexity or both).

In assessing and training movement quality it is important to understand what movement quality is and which factors may affect performance.66 Movement quality after ACL injury has been defined as ‘the ability to control the limbs and achieve sufficient balance and kinematic alignment during functional activities, not displaying movement asymmetries or risk factors linked to ACL injuries’.8,66 Importantly, the definition makes no reference to what is acceptable loss of balance or deviation of kinematics away from normal, or actually what normal or ideal is.66 In fact, it is thought there likely exists no ’ideal’ or ‘perfect’ way to move.66 According to the dynamic systems theory,81 there are multiple factors which can influence the expression of movement quality, which should be considered when training and assessing movement quality.66 These can be summarized as a complex interaction between individual (organistic constraints), task constraints and the environment or context in which the task is been performed (environmental constraints).

Despite the ambiguity in assessing movement quality, it is here and elsewhere8,9,76 proposed to utilize a relatively simple qualitative movement analysis method to support progression through tasks and through ACL rehabilitation stages as part of criterion based rehabilitation. This can provide information on movement quality during the tasks at hand, and to be able to provide feedback to the patient, to create a continuous learning environment to solve the task and optimally progress.76 It is suggested to monitor the patient’s ability to maintain control of the body utilizing teaching and training of optimal frontal plane (pelvis, trunk and lower limb, Figure 2a) and sagittal plane control (Figure 2b), depending upon the specific task.76 If the tasks cannot be performed at a minimum task competency, then the tasks should be simplified.8 Qualitatively assessing movement quality (frontal and sagittal plane) as part of the ACL functional recovery process during foundation, landing, plyometric and sport-specific tasks is also recommended. This can provide some objective guidance to support criterion driven ACL functional recovery.8,9,82

59306 Figure 2: A, an easy to utilize and teach model of movement analysis based on three lines in the frontal plane, with a line to assess trunk stability/ alignment, pelvis stability/alignment and limb stability/alignment. B, depicts the sagittal plane view which is dependent upon the task but a function of ankle to knee and knee to hip alignments. From Buckthorpe et al.75

Can they tolerate the level of loading?

A key part of optimal load management is adjusting the training according to the response to exercise. Any functional based progression has to be in line with the biological healing and ability of the joint to withstand the loading demands. Pain and swelling can be used to determine exercise based progressions as these factors will relate to the loading stress experienced by the knee.9,83 Progression to more intense or complex tasks should only be allowed when there is no or minimal pain (e.g., 0-2 on the numeric rating scale)83 or swelling (stroke test) increase in response to previous tasks.83 Pain and/or swelling response would indicate excessive previous loading levels to the knee joint and an adverse reactions, which may then limit optimal adaptation. Furthermore, after unaccustomed exercise, there may be an exercise induced muscle reaction, resulting in delayed onset muscle soreness.84 The degree of muscle reaction depends on many factors including exercise type, duration, intensity and habituation to the exercise.85,86 Tasks that are too strenuous will result in significant muscle reaction, which may take substantial time to recover and may limit the ability to train in the subsequent days. Monitoring the muscle soreness can provide an indication of the muscle specific loading and required recovery time, which can then support subsequent training modifications.

Plyometric progressions after ACLR- A Four-staged program aligned to the rehabilitation pathway after ACLR

For effective design of plyometric programs for the ACLR patient, it is imperative that any such program be aligned to the functional recovery approach and overall goals as a whole. These goals include restoring knee specific factors, neuromuscular function of many muscle groups and types of function (e.g., maximal isolated and functional strength and explosive neuromuscular performance), movement quality and sport-specific fitness.8,9 Although, there is still not an international consensus on ACL rehabilitation, there has been considerable research recently published toward standardizing the ACL rehabilitation journey. Current best practice for ACL rehabilitation appears to involve criterion-based rehabilitation through a series of stages.8,9,87 The functional recovery process can be broadly separated into pre-operative, early, mid and late stage rehabilitation and RTS training.8,9

Below is presented a four-staged plyometric program aligned to the ACL functional recovery process. This considers i) the plyometric tasks and associated intensity and complexity, ii) the required movement quality and strength to perform these tasks and iii) monitoring considerations, specifically daily monitoring (e.g., pain and swelling, soreness rules) but also monitoring as part of criterion-based ACL functional recovery. In general, the program has some rules or themes which include progressions in intensity and specificity of the movements with progressive increases in entry speeds (vertical loading height/ horizontal velocity), a gradual reduction in GCT, progression from bilateral to unilateral tasks and from linear (vertical to horizontal to lateral) to multi-planar tasks. Furthermore, it is recommended to use different surfaces, beginning with more compliant surfaces and progressing to stiffer surfaces (Figure 3).

59307 Figure 3: Possible progressions on use of surfaces for plyometric training in ACL reconstructed athlete or load compromised individuals

Progressions through stages and exercises within the stage is based on good quality performance of the tasks, ideally no or only minimal pain (e.g., <2/10 on numeric rating scale)83 and/or swelling of the joint to the specific loading demands83 and continued improvement in lower limb strength. Each stage should be completed in sequence and an athlete cannot perform any task in the stage without meeting the specific stage criteria (Table 2). As it aligns to the rehabilitation process after ACLR, meeting specific criteria as part of criterion based rehabilitation is recommended. The four-stage program compliments and aligns to the authors published ACL functional recovery programs.8,9 These involve comprehensive overviews of the mid-stage,8 late-stage and RTS training stages.9 The plyometric program begins in the mid-stage of rehabilitation (Stage 1), with Stages 2 and 3 aligned to the late-stage and Stage 4 to the RTS training stage.

Stage 1 of the program uses low intensity plyometrics, characterized as bilateral off-set and bilateral asymmetrical, but also with sub-maximal bilateral symmetrical tasks (to support movement re-training). The rise in height of the center of mass above neutral position is typically minimal. GCTs should be long (> 1-2s) and the main theme is to support movement retraining, primarily with a focus to support treadmill gait re-education.9 Estimated GRFs are less than two-times body mass per limb. The program is completed alongside foundation movement re-education, functional strengthening (e.g., squat, deadlift, single leg progressions), bilateral landing tasks and isolated strength training.7 Importantly, during this first stage, which occurs during the mid-stage of rehabilitation after ACLR, the patient will have significant knee extensor strength deficits. Knee extensor weakness is a significant barrier to been able to perform functional tasks.77 Furthermore, significant strength deficits result in biomechanical compensatory strategies. This may include compensatory use of the hip extensors instead of the knee extensors during unilateral tasks or compensatory loading of the un-injured limb during bilateral tasks.88–90 Even when achieving the optimal kinematics (e.g. correcting the compensatory movement pattern of greater hip to knee flexion), there is still typically inhibition of the quadriceps, resulting in lower neuromuscular recruitment, which may result in insufficient stimulus for adaptation.89 As such, the benefits of plyometric training for strength development is likely minimal in this stage. It is essential to ensure optimal technique during the movements,64,65 ideally using real-time biofeedback,64 to support appropriate motor learning. Poor task selection may result in movement compensations,49,64 which could interfere with optimal motor repatterning.65 Thus, quality over quantity and intensity is recommended. It is essential to focus on isolated strengthening techniques to overcome the quadriceps weakness and restore normal quadriceps strength during this stage.7 In terms of recommended plyometric tasks for this stage, these can be seen in figures 4 to 6 and within Table 2.

59309 Figure 4: A lunge push-back. The patient steps forward as if performing a lunge (A) and then decelerates their momentum and pushes back with power to arrive back at the starting standing position (B).

Stage 2 of the program commences when the athlete can achieve the necessary late-stage rehabilitation criteria (Table 2). This means they must have a good single leg squat (defined as good control of the movement with no presence of excessive dynamic knee valgus, altered motor strategy or trunk and pelvis deviations),8 sufficient closed kinetic chain (single leg loads > 1.25 times body mass) and knee extensor limb symmetric index (>80%, LSI) and able to run on the treadmill with good kinematics.8,9 Key themes of late-stage ACL rehabilitation are developing single limb eccentric control (deceleration/landing) and restoring power and maximal eccentric strength.9 However, there is a strong use of bilateral plyometric tasks for developing explosive lower limb strength and high load mechanics. The stage now allows for maximal effort bilateral plyometrics for automatization of the motor pattern, but more specifically for improving kinetics in explosive movement tasks. Consideration though of landing height is needed. A key aim of the stage is to achieve a good bilateral drop jump (kinetics and kinematics) (30 cm) and single leg landing/deceleration control. Example tasks can be seen in Figures 7 to 10 and within Table 2.

59308 Table 2: A plyometric program approach across four stages aligned to the functional recovery framework after ACL reconstruction. Particular training goals, use of plyometrics, progression criteria, training planning considerations, with specific movement exercises and progressions are presented.

Stage	1	2	3	4	
Typical weeks*	10-14	15-18	19-22	23-29	
General goals of stage	Full recovery of joint R.O.M
Restoration of muscle strength imbalances to within 20% of ‘trained’ contralateral limb (or pre-injury strength values)
Recovery of basic motor patterning and running gait
Avoid physical fitness de-training	Develop functional strength
Develop closed chain eccentric strength
Develop bilateral power
Develop unilateral eccentric control Continue to restore lower limb muscle imbalances	Restore neuromuscular function markers to within at least 10% (knee and adjacent joint specific strength and closed kinetic chain and power)
Restore high load movement quality
Restore aerobic fitness	Restore sports specific movement quality, fitness, skills and develop movement ‘volumes’ to prepare for RTS	
Plyometric use	Low intensity predominantly bilateral plyometrics at sub-maximal intensity to support eccentric/motor control and preparation for running	Moderate intensity bilateral and unilateral plyometrics with view to developing lower limb power and eccentric control, particularly unilateral deceleration capabilities	Higher intensity bilateral and unilateral plyometrics with view to developing lower limb power and multipolar motor control and acceleration capabilities	Optimise lower limb explosive neuromuscular performance and support sport-specific movement re-training. Mindful of load management	
Criteria to enter plyometric stage	0-1 pain NRS @ rest <2 pain during activities of daily living
Full knee extension
Knee flexion > 120°
Good BL squat (body weight and loaded) with < 20% asymmetry in loading8
Isometric knee extensor LSI >70%	Ability to run of treadmill for 10 mins @8km/h8
Good BL landing kinematics
Good SL squat kinematics
Closed chain strength > 1.25 times body mass (8RM) or 1.5 x times body mass (1RM/peak isometric force)
Isokinetic LSI knee extensor and flexor >80%	Good BL drop jump mechanics
Good SL landing control
Closed chain strength > 1.5 times body mass (8RM) or 2 x times body mass (1RM/peak isometric force)	Isokinetic LSI knee extensor and flexor >90%9
Closed chain strength > 1.5 times body mass (8RM) or 2 x times body mass (1RM/peak isometric force)9
Good pre-planned movement quality (UL landing/deceleration/ BL and UL drop jump/ CoD mechanics indoor and/or OF)	
Training planning	Intensity	Low	Moderate	High	Very high	
Plyometric type	BL off-set
BL asymmetrical
BL symmetrical (sub-max)	BL off-set
BL asymmetrical
BL symmetrical
UL (linear)	Bilateral off-set
Bilateral asymmetrical
Bilateral symmetrical
UL (multi-planar)	Bilateral off-set
Bilateral asymmetrical
Bilateral symmetrical
UL (multi-planar)	
Volume (foot contacts)	50	100	150	200	
Plyometric Tasks	Lunge push back
SJ to box
CMJ to box
Skips in place
Step up jump (same leg)
Step up jump (alternating)
Step and hold (forward)	BL SJ (in place, forward)
BL CMJ (in place, forward)
BL drop jump (30 cm box)
Split jump (same leg land)
Split jump (alternating)
Step and land (forward, lateral, standing and from running on spot)
Step-land-push back (forward, lateral, standing and from running on spot)	UL SJ/CMJ to BL landing
UL SJ/CMJ to box
Rotational jump and land
Lateral step-jump-back
Tuck jump
Step cut (30°/45°/60°/90°)
Hop singular (in place/ forward/ lateral/45°/90°)
Hop multiple (in place/ forward/ lateral/45°/90°)
SL drop jump (box/in place/lateral to box)
Advanced bounding OF	CMJ (hurdles)
SJ/CMJ weighted
BL/UL DJ (increased height to box)
Lateral hop (band/rope/ med ball)
SL 90 lateral drop jump
Step cut (perturbation)
OF agility drills
OF CoD drills with perturbation/ external focus and sport-specific environment	
Other movement tasks	SL movement progressions (from BL squat to UL squat)
Bilateral landing from step
Trampoline SL landing
Re-integration to treadmill running
Stage 2 plyometrics in pool (~60% body height)	Treadmill running (12-20 km/h)
Outdoor linear movements (running, ladder drills, lateral shuffle)
Stage 3 plyometrics in pool (~60% body height)	Outdoor pre-planned coordination program (multi-directional movement demands)
High speed linear running/sprinting	On-field sport-specific training with re-active movements, contact/perturbation drills, as well as skills training	
R. O. M, range of motion; NRS, numeric rating scale; BL, bilateral; LSI, limb symmetry index; SJ, squat jump; CMJ, countermovement jump; RM, repetition maximum; SL, single leg; UL, unilateral; OF, on-field; RTS, return-to-sport; CoD, change of direction; DJ, drop jump * time is only indicative, and the protocol should be always customized on patient’s response.

59310 Figure 5: A sub-maximal bilateral jump (countermovement or squat) with controlled landing with a focus on eccentric acceptance and good ankle, knee and hip flexion angles. Preforming this on sand or similar surface will reduce peak ground reaction forces allowing for a longer dissipation of force.

59311 Figure 6: Example of performing a bilateral jump onto a box, either from squat or countermovement jump. The box will allow for an increased focus on concentric power development and slow stretch-shortening cycle with the countermovement jump, while reducing the landing impact forces due to limiting the height the patient will land from.

59312 Figure 7: Images of a countermovement or squat jump in place with maximal height. The removal of the box results in higher landing forces due to landing from a higher height.

59313 Figure 8: A single leg drop jump in the pool which can be performed one stage earlier at an appropriate depth (around 1 m) or waist height.

59314 Figure 9: The tuck jump performed on sand. The patient lands (A) and immediately jumps again (B) raising their legs with symmetrical heights and alignments before landing (C) and repeating the action for a series of jumps. As the patient would land from the maximal height of the jump, the landing intensity is typically higher than that of the drop jump.

59315 Figure 10: A lateral jump from left to right limb (A) with controlled landing and stabilization (B).

Stage 3 transitions to a greater use of unilateral plyometrics and is performed in conjunction with a multi-directional on-field coordination program (pre-planned coordination tasks). It transitions from forward and vertical unilateral plyometric to lateral and then multidirectional unilateral plyometric tasks. The key aim by the end of the stage is to have good kinematics during high speed change of direction and good single leg drop jump and hop performance (multiplanar). Ideally movement quality would be confirmed using qualitative analysis of sagittal and frontal plane kinematics, using high speed (e.g., 240Hz) camera systems.9,66 Unilateral plyometrics play a key role in supporting movement progressions and unilateral control, whilst bilateral plyometrics are used to support enhancements in neuromuscular function (strength, power and RFD) in this stage. Key aspects of the unilateral exercises are to support enhanced motor control with gradually reducing GCT to mimic sport-type tasks (e.g., progressing from 1-2 s GCT to 0.25-0.4 s GCT). Example tasks can be seen in figures 11 to 14 and within Table 2.

59316 Figure 11: Loaded bilateral countermovement or squat jumps

59317 Figure 12: A lateral jump from left to right limb (A) with landing (B) and immediate jump back to the right limb (C), as opposed to just landing in which occurs during Stage 2.

59318 Figure 13: A single leg drop jump with use of other box to challenge control and reduce final landing heights.

59319 Figure 14: Use of on-field for higher intensity running and bounding exercises.

59320 Figure 15: A lateral jump and return with A) a rope and B) medicine ball to create perturbation and/or exaggerated lateral momentum

Stage 4 builds on Stage 3 and focuses on the use of maximal unilateral plyometric tasks for motor pattern automatization as well as enhancement in neuromuscular performance. Furthermore, in terms of motor patterning, a key aim of the stage as a whole is to progress to re-active movements and prepare for sport-specific training (Table 2). Creating perturbations during plyometric tasks to challenge neuromuscular control is recommended (Figure 15). A key aim of the stage is to achieve good re-active movement performance under sporting type tasks to prepare for sport-specific practice. To RTS, it is recommended to possess good movement quality during sport-type tasks and under sport-specific situations.8 It is recommended to visually assess and use video recordings of sport-specific movements (e.g., reactive cutting or change of direction at an obstacle) during on-field sessions and/or specific field based assessments.66 Patients should also have completed an on-field rehabilitation process,91 corrected muscle strength imbalances8,12,80 and restored their physical fitness.9 This of course is typically after medical clearance from sports medicine physician and/or surgeon has been allowed.8

SUMMARY

This clinical commentary presents a four-stage plyometric program for the ACLR athlete, which can be undertaken as part of criterion-based rehabilitation. Plyometric training should form a key component of the functional recovery process after ACLR. Used effectively, plyometrics can support enhancements in strength, movement quality, explosive neuromuscular function and athletic performance.27–30,33,34,59,60 Plyometric intensity is based on the intensity of efforts, the vertical and or horizontal momentums/velocities prior to impact, the ability of the neuromuscular system to accept those loads, the GCT, the surface compliance/environment (e.g., land or pool) and movement quality during the task. It is important to align the plyometric program to the overall ACL functional recovery program and overall functional recovery status of the athlete. There should be a gradual increase in task intensity and specificity and all tasks should be used for neuromuscular and/or motor control re-conditioning.

Conflict of interest

The authors report no conflict of interests relevant to the content of this review.
==== Refs
Return to pre-injury level of competitive sport after anterior cruciate ligament reconstruction surgery: two-thirds of patients have not returned by 12 months after surgery The American Journal of Sports Medicine Ardern Clare L. Webster Kate E. Taylor Nicholas F. Feller Julian A. 2011
39 3 538 543 0363-5465 10.1177/0363546510384798 10.1177/0363546510384798 21098818
Career length and injury incidence after anterior cruciate ligament reconstruction in major league soccer players Orthop J Sports Med Arundale A.J.H. Silvers-Granelli H.J. Snyder-Mackler L. 1 2018
24;6(1):2325967117750825
Knee function, strength and resumption of preinjury sports participation in young athletes following anterior cruciate ligament reconstruction Journal of Orthopaedic & Sports Physical Therapy Ithurburn Matthew P. Longfellow Matthew A. Thomas Staci Paterno Mark V. Schmitt Laura C. 3 2019
49 3 145 153 0190-6011 10.2519/jospt.2019.8624 10.2519/jospt.2019.8624 30770031
ACL injuries in men's professional football: A 15-year prospective study on time trends and return-to-play rates reveals only 65% of players still play at the top level 3 years after ACL rupture British Journal of Sports Medicine Waldén Markus Hägglund Martin Magnusson Henrik Ekstrand Jan BMJ 31 3 2016
50 12 744 750 0306-3674 10.1136/bjsports-2015-095952 10.1136/bjsports-2015-095952
Exploring the high reinjury rate in younger patients undergoing anterior cruciate ligament reconstruction The American Journal of Sports Medicine Webster Kate E. Feller Julian A. SAGE Publications 20 7 2016
44 11 2827 2832 0363-5465 10.1177/0363546516651845 10.1177/0363546516651845
Risk of secondary injury in younger athletes after anterior cruciate ligament reconstruction: A systematic review and meta-analysis The American Journal of Sports Medicine Wiggins Amelia J. Grandhi Ravi K. Schneider Daniel K. Stanfield Denver Webster Kate E. Myer Gregory D. SAGE Publications 15 1 2016
44 7 1861 1876 0363-5465 10.1177/0363546515621554 10.1177/0363546515621554 26772611
Incidence of second ACL injuries 2 years after primary ACL reconstruction and return to sport The American Journal of Sports Medicine Paterno Mark V. Rauh Mitchell J. Schmitt Laura C. Ford Kevin R. Hewett Timothy E. SAGE Publications 21 4 2014
42 7 1567 1573 0363-5465 10.1177/0363546514530088 10.1177/0363546514530088 24753238
Optimising the late-stage rehabilitation and return-to-sport training and testing process after ACL reconstruction Sports Medicine Buckthorpe Matthew Springer Science and Business Media LLC 19 4 2019
49 7 1043 1058 0112-1642 10.1007/s40279-019-01102-z 10.1007/s40279-019-01102-z
Optimising the 'mid-stage' training and testing process after ACL reconstruction Sports Medicine Buckthorpe Matthew Della Villa Francesco 2020
50 4 657 678 0112-1642 10.1007/s40279-019-01222-6 10.1007/s40279-019-01222-6 31782065
Benefits and use of aquatic therapy during rehabilitation after ACL reconstruction -a clinical commentary International Journal of Sports Physical Therapy Buckthorpe Matthew Pirotti Elisa Villa Francesco Della 12 2019
14 6 978 993 2159-2896 10.26603/ijspt20190978 10.26603/ijspt20190978
The time has come to incorporate a greater focus on rate of force development training in the sports injury rehabilitation process Muscle Ligaments and Tendons Journal Buckthorpe M. Roi G.S. 2018
7 3 435 441 10.32098/mltj.03.2017.05 10.32098/mltj.03.2017.05
Restoring knee extensor strength after anterior cruciate ligament reconstruction: A clinical commentary International Journal of Sports Physical Therapy Buckthorpe Matthew La Rosa Giovanni Villa Francesco Della The Sports Physical Therapy Session 2 2019
14 1 159 172 2159-2896 10.26603/ijspt20190159 10.26603/ijspt20190159
Only one patient out of five achieves symmetrical knee function 6 months after primary anterior cruciate ligament reconstruction Knee Surgery, Sports Traumatology, Arthroscopy Cristiani Riccardo Mikkelsen Christina Forssblad Magnus Engström Björn Stålman Anders Springer Science and Business Media LLC 18 2 2019
27 11 3461 3470 0942-2056 10.1007/s00167-019-05396-4 10.1007/s00167-019-05396-4 30778627
Maximizing quadriceps strength after ACL reconstruction Clinics in Sports Medicine Palmieri-Smith Riann M. Thomas Abbey C. Wojtys Edward M. 7 2008
27 3 405 424 0278-5919 10.1016/j.csm.2008.02.001 10.1016/j.csm.2008.02.001 18503875
Rate of force development as an adjunctive outcome measure for return-to-sport decisions after anterior cruciate ligament reconstruction Journal of Orthopaedic & Sports Physical Therapy Angelozzi Massimo Madama Marco Corsica Cristiana Calvisi Vittorio Properzi Gianfranco McCaw Steven T. Cacchio Angelo Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 9 2012
42 9 772 780 0190-6011 10.2519/jospt.2012.3780 10.2519/jospt.2012.3780 22814219
The effect of anterior cruciate ligament reconstruction on hamstring and quadriceps muscle function outcome ratios in male athletes Srpski arhiv za celokupno lekarstvo Kadija Marko Knezevic Olivera M. Milovanovic Darko Nedeljkovic Aleksandar Mirkov Dragan M. National Library of Serbia 2016
144 3-4 151 157 0370-8179 10.2298/sarh1604151k 10.2298/sarh1604151k 27483559
Lower limb asymmetry in mechanical muscle function: A comparison between ski racers with and without ACL reconstruction Scandinavian Journal of Medicine & Science in Sports Jordan M. J. Aagaard P. Herzog W. Wiley 2015
25 3 e301 e309 0905-7188 10.1111/sms.12314 10.1111/sms.12314 25212216
Landing adaptations after ACL reconstruction Medicine & Science in Sports & Exercise Decker MICHAEL J. Torry MICHAEL R. Noonan THOMAS J. Riviere AMY Sterett WILLIAM I. 9 2002
34 9 1408 1413 0195-9131 10.1097/00005768-200209000-00002 10.1097/00005768-200209000-00002 12218731
Motion alterations after anterior cruciate ligament reconstruction: Comparison of the injured and uninjured lower limbs during a single-legged jump J Athl Train de Fontenay Benoît Pairot Argaud Sebastien Blache Yoann Monteil Karine 1 6 2014
49 3 311 316 1062-6050 10.4085/1062-6050-49.3.11 10.4085/1062-6050-49.3.11 24840584
Anterior cruciate ligament injury alters preinjury lower extremity biomechanics in the injured and uninjured leg: The JUMP-ACL study British Journal of Sports Medicine Goerger Benjamin M Marshall Stephen W Beutler Anthony I Blackburn J Troy Wilckens John H Padua Darin A BMJ 2015
49 3 188 195 0306-3674 10.1136/bjsports-2013-092982 10.1136/bjsports-2013-092982 24563391
Persons with reconstructed ACL exhibit altered knee mechanics during high speed maneuvers International Journal of Sports Medicine Lee S.-P. Chow J. Tillman M. 9 1 2014
35 6 528 533 0172-4622 10.1055/s-0033-1358466 10.1055/s-0033-1358466
Limb asymmetries in landing and jumping 2 years following anterior cruciate ligament reconstruction Clin J Sports Med Paterno Mark V Ford Kevin R Myer Gregory D Heyl Rachel Hewett Timothy E 7 2007
17 4 258 262 1050-642X 10.1097/jsm.0b013e31804c77ea 10.1097/jsm.0b013e31804c77ea
Abnormal frontal plane knee mechanics during sidestep cutting in female soccer athletes after anterior cruciate ligament reconstruction and return to sport The American Journal of Sports Medicine Stearns Kristen M. Pollard Christine D. SAGE Publications 20 2 2013
41 4 918 923 0363-5465 10.1177/0363546513476853 10.1177/0363546513476853
Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: A prospective study The American Journal of Sports Medicine Hewett Timothy E. Myer Gregory D. Ford Kevin R. Heidt Robert S. Jr. Colosimo Angelo J. McLean Scott G. van den Bogert Antonie J. Paterno Mark V. Succop Paul SAGE Publications 4 2005
33 4 492 501 0363-5465 10.1177/0363546504269591 10.1177/0363546504269591 15722287
Biomechanical measures during landing and postural stability predict second anterior cruciate ligament after anterior cruciate ligament reconstruction and return to sport The American Journal of Sports Medicine Paterno Mark V. Schmitt Laura C. Ford Kevin R. Rauh Mitchell J. Myer Gregory D. Huang Bin Hewett Timothy E. 11 8 2010
38 10 1968 1978 0363-5465 10.1177/0363546510376053 10.1177/0363546510376053 20702858
Prospectively identified deficits in sagittal plane hip–ankle coordination in female athletes who sustain a second anterior cruciate ligament injury after anterior cruciate ligament reconstruction and return to sport Clinical Biomechanics Paterno Mark V. Kiefer Adam W. Bonnette Scott Riley Michael A. Schmitt Laura C. Ford Kevin R. Myer Gregory D. Shockley Kevin Hewett Timothy E. 12 2015
30 10 1094 1104 0268-0033 10.1016/j.clinbiomech.2015.08.019 10.1016/j.clinbiomech.2015.08.019 26416200
Current concepts of plyometric exercise Int J Sports Phys Ther Davies G. Riemann B.L. Manske R. 2015
10 6 760 786 26618058
The effects of plyometric training on change-of-direction ability: a meta-analysis Int J Sports Physiol Perform Asadi Abbas Arazi Hamid Young Warren B. de Villarreal Eduardo Sáez 7 2016
11 5 563 573 1555-0265 10.1123/ijspp.2015-0694 10.1123/ijspp.2015-0694 27139591
The effect of neuromuscular training on the incidence of knee injury in female athletes. A prospective study The American Journal of Sports Medicine Hewett Timothy E. Lindenfeld Thomas N. Riccobene Jennifer V. Noyes Frank R. 11 1999
27 6 699 706 0363-5465 10.1177/03635465990270060301 10.1177/03635465990270060301
Comparison of land-based and aquatic-based plyometric programmes during 8-week training period J Sport Rehabil Miller Michael G. Berry David C. Bullard Susan Gilders Roger 11 2002
11 4 268 283 1056-6716 10.1123/jsr.11.4.268 10.1123/jsr.11.4.268
The effects of plyometric versus dynamic stabilization and balance training on lower extremity biomechanics The American Journal of Sports Medicine Myer Gregory D. Ford Kevin R. McLean Scott G. Hewett Timothy E. SAGE Publications 3 2006
34 3 445 455 0363-5465 10.1177/0363546505281241 10.1177/0363546505281241 16282579
Does plyometric training improve strength performance? A meta-analysis Journal of Science and Medicine in Sport Sáez-Sáez de Villarreal Eduardo Requena Bernardo Newton Robert U. 9 2010
13 5 513 522 1440-2440 10.1016/j.jsams.2009.08.005 10.1016/j.jsams.2009.08.005 19897415
Muscle power and fiber characteristics following 8 weeks of plyometric training J Strength Cond Res Potteiger J.A. Lockwood R.H. Haub M.D.. 1999
13 275 9
The effects of plyometric training on sprint performance: A meta-analysis J Strength Cond Res Sáez de Villarreal Eduardo Requena Bernardo Cronin John B 2 2012
26 2 575 584 1064-8011 10.1519/jsc.0b013e318220fd03 10.1519/jsc.0b013e318220fd03
Strength and functional symmetry is associated with post-operative rehabilitation in patients following anterior cruciate ligament reconstruction Knee Surgery, Sports Traumatology, Arthroscopy Ebert Jay R. Edwards Peter Yi Luke Joss Brendan Ackland Timothy Carey-Smith Richard Buelow Jens-Ulrich Hewitt Ben Springer Science and Business Media LLC 2018
26 8 2353 2361 0942-2056 10.1007/s00167-017-4712-6 10.1007/s00167-017-4712-6
Ground reaction forces in distance running Journal of Biomechanics Cavanagh Peter R. Lafortune Mario A. 1 1980
13 5 397 406 0021-9290 10.1016/0021-9290(80)90033-0 10.1016/0021-9290(80)90033-0
Hip and knee joint loading during vertical jumping and push jerking Clinical Biomechanics Cleather Daniel J. Goodwin Jon E. Bull Anthony M.J. 1 2013
28 1 98 103 0268-0033 10.1016/j.clinbiomech.2012.10.006 10.1016/j.clinbiomech.2012.10.006 23146164
Two-leg squat jumps in water: An effective alternative to dry land jumps International Journal of Sports Medicine Colado J. C. Garcia-Masso X. González L.-M. Triplett N. T. Mayo C. Merce J. Georg Thieme Verlag KG 2010
31 02 118 122 0172-4622 10.1055/s-0029-1242814 10.1055/s-0029-1242814 20222004
Impact forces of plyometric exercises performed on land and in water Sports Health: A Multidisciplinary Approach Donoghue Orna A. Shimojo Hirofumi Takagi Hideki SAGE Publications 8 4 2011
3 3 303 309 1941-7381 10.1177/1941738111403872 10.1177/1941738111403872 23016022
Quantifying plyometric intensity via rate of force development, knee joint, and ground reaction forces J Strength Cond Res Jensen R.L. Ebben W.P. 2007
21 3 763 767 17685678
Optimal loading: Key variables and mechanisms British Journal of Sports Medicine Glasgow Philip Phillips Nicola Bleakley Christopher BMJ 6 1 2015
49 5 278 279 0306-3674 10.1136/bjsports-2014-094443 10.1136/bjsports-2014-094443
Effect of landing stiffness on joint kinetics and energetics in the lower extremity Medicine & Science in Sports & Exercise Devita PAUL Skelly WILLIAM A. 1 1992
24 1 108 115 0195-9131 10.1249/00005768-199201000-00018 10.1249/00005768-199201000-00018
Understanding and preventing acl injuries: Current biomechanical and epidemiologic considerations - update 2010 N Am J Sports Phys Ther Hewett T.E. Ford K.R. Hoogenboom B.J.. 2010
5 4 234 251 21655382
Sex differences in lower extremity biomechanics during single leg landings Clinical Biomechanics Schmitz Randy J. Kulas Anthony S. Perrin David H. Riemann Bryan L Shultz Sandra J. 7 2007
22 6 681 688 0268-0033 10.1016/j.clinbiomech.2007.03.001 10.1016/j.clinbiomech.2007.03.001 17499896
Contributions of lower extremity joints to energy dissipation during landings Medicine & Science in Sports & Exercise Zhang SONG-NING Bates BARRY T. Dufek JANET S. 4 2000
32 4 812 819 0195-9131 10.1097/00005768-200004000-00014 10.1097/00005768-200004000-00014 10776901
Effect of plyometric training on sand versus grass on muscle soreness and jumping and sprinting ability in soccer players British Journal of Sports Medicine Impellizzeri F M Rampinini E Castagna C Martino F Fiorini S Wisloff U 5 6 2007
42 1 42 46 0306-3674 10.1136/bjsm.2007.038497 10.1136/bjsm.2007.038497 17526621
Aquatic-based rehabilitation and training for the elite athlete Journal of Orthopaedic & Sports Physical Therapy Thein Jill M. Brody Lori Thein Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 1 1998
27 1 32 41 0190-6011 10.2519/jospt.1998.27.1.32 10.2519/jospt.1998.27.1.32
A 'plane' explanation of anterior cruciate ligament injury mechanisms: a systematic review Sports Medicine Quatman Carmen E. Quatman-Yates Catherine C. Hewett Timothy E. 9 2010
40 9 729 746 0112-1642 10.2165/11534950-000000000-00000 10.2165/11534950-000000000-00000 20726620
The influence of abnormal hip mechanics on knee injury: A biomechanical perspective Journal of Orthopaedic & Sports Physical Therapy Powers Christopher M. Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 2 2010
40 2 42 51 0190-6011 10.2519/jospt.2010.3337 10.2519/jospt.2010.3337
Neuromuscular risk factors for knee and ankle ligament injuries in male youth soccer players Sports Medicine Read Paul J. Oliver Jon L. De Ste Croix Mark B. A. Myer Gregory D. Lloyd Rhodri S. Springer Science and Business Media LLC 8 2 2016
46 8 1059 1066 0112-1642 10.1007/s40279-016-0479-z 10.1007/s40279-016-0479-z 26856339
Jumper’s knee or lander’s knee? A systematic review of the relation between jump biomechanics and patellar tendinopathy International Journal of Sports Medicine Van der Worp H. de Poel H. Diercks R. van den Akker-Scheek I. Zwerver J. Georg Thieme Verlag KG 27 2 2014
35 08 714 722 0172-4622 10.1055/s-0033-1358674 10.1055/s-0033-1358674
Sagittal-plane trunk position, landing forces, and quadriceps electromyographic activity J Athl Train Blackburn J. Troy Padua Darin A. 1 3 2009
44 2 174 179 1062-6050 10.4085/1062-6050-44.2.174 10.4085/1062-6050-44.2.174 19295962
Rehabilitation of patellar tendinopathy using hip extensor strengthening and landing-strategy modification: Case report with 6-month follow-up Journal of Orthopaedic & Sports Physical Therapy Silva Rodrigo Scattone Ferreira Ana Luisa G. Nakagawa Theresa H. Santos José E. M. Serrão Fábio V. Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 11 2015
45 11 899 909 0190-6011 10.2519/jospt.2015.6242 10.2519/jospt.2015.6242
The mechanical consequences of dynamic frontal plane limb alignment for non-contact ACL injury Journal of Biomechanics Chaudhari Ajit M. Andriacchi Thomas P. 1 2006
39 2 330 338 0021-9290 10.1016/j.jbiomech.2004.11.013 10.1016/j.jbiomech.2004.11.013
Combined knee loading states that generate high anterior cruciate ligament forces Journal of Orthopaedic Research Markolf Keith L. Burchfield Daniel M. Shapiro Matthew M. Shepard Michael F. Finerman Gerald A. M. Slauterbeck James L. Wiley 11 1995
13 6 930 935 0736-0266 10.1002/jor.1100130618 10.1002/jor.1100130618
Sagittal plane biomechanics cannot injure the ACL during sidestep cutting Clinical Biomechanics McLean Scott G. Huang Xuemei Su Anne van den Bogert Antonie J. 10 2004
19 8 828 828 0268-0033 10.1016/j.clinbiomech.2004.06.006 10.1016/j.clinbiomech.2004.06.006
Restrained tibial rotation may prevent ACL injury during landing at different flexion angles The Knee Mokhtarzadeh Hossein Ng Andrew Yeow Chen Hua Oetomo Denny Malekipour Fatemeh Lee Peter Vee Sin 1 2015
22 1 24 29 0968-0160 10.1016/j.knee.2014.09.012 10.1016/j.knee.2014.09.012
Current concepts for injury prevention in athletes after anterior cruciate ligament reconstruction The American Journal of Sports Medicine Hewett Timothy E. Di Stasi Stephanie L. Myer Gregory D. SAGE Publications 2013
41 1 216 224 0363-5465 10.1177/0363546512459638 10.1177/0363546512459638 23041233
Meta-analysis of meta-analyses of anterior cruciate ligament injury reduction training programs Journal of Orthopaedic Research® Webster Kate E. Hewett Timothy E. Wiley 13 6 2018
36 10 2696 2708 0736-0266 10.1002/jor.24043 10.1002/jor.24043
Critical components of neuromuscular training to reduce ACL injury risk in female athletes: Meta-regression analysis British Journal of Sports Medicine Sugimoto Dai Myer Gregory D Barber Foss Kim D Pepin Michael J Micheli Lyle J Hewett Timothy E BMJ 1 6 2016
50 20 1259 1266 0306-3674 10.1136/bjsports-2015-095596 10.1136/bjsports-2015-095596 27251898
The effect of a hip-strengthening program on mechanics during running and during a single-leg squat Journal of Orthopaedic & Sports Physical Therapy Willy Richard W. Davis Irene S. Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 9 2011
41 9 625 632 0190-6011 10.2519/jospt.2011.3470 10.2519/jospt.2011.3470 21765220
Effects of muscle strengthening on vertical jump height: A simulation study Med Sci Sports Exerc Bobbert M.F. Van Soest A.J. 1994
26 1012 1010 7968418
Motor learning and performance Schmidt R.A.W.C. Human Kinetics;2005 Champaign
Gluteus maximus dysfunction: its relevance to athletic performance and injury and how to treat it—a clinical commentary International Journal of Sports Physical Therapy Buckthorpe Matthew Stride Matthew Villa Francesco Della 7 2019
14 4 655 669 2159-2896 10.26603/ijspt20190655 10.26603/ijspt20190655 31440415
Principles of sensorimotor learning Nature Reviews Neuroscience Wolpert Daniel M. Diedrichsen Jörn Flanagan J. Randall Springer Science and Business Media LLC 27 10 2011
12 12 739 751 1471-003X 10.1038/nrn3112 10.1038/nrn3112
Recommendations for movement re-training after ACL reconstruction Sports Medicine Buckthorpe Matthew 11 4 2021
0112-1642 10.1007/s40279-021-01454-5 10.1007/s40279-021-01454-5
Anterior cruciate ligament fatigue failures in knees subjected to repeated simulated pivot landings The American Journal of Sports Medicine Lipps David B. Wojtys Edward M. Ashton-Miller James A. SAGE Publications 4 3 2013
41 5 1058 1066 0363-5465 10.1177/0363546513477836 10.1177/0363546513477836 23460331
Biomechanical overload syndrome: Defining a new diagnosis British Journal of Sports Medicine Franklyn-Miller Andrew Roberts Andrew Hulse David Foster John BMJ 2014
48 6 415 416 0306-3674 10.1136/bjsports-2012-091241 10.1136/bjsports-2012-091241 22983122
Predictors and effects of patellofemoral pain following hamstring-tendon ACL reconstruction Journal of Science and Medicine in Sport Culvenor Adam G. Collins Natalie J. Vicenzino Bill Cook Jill L. Whitehead Timothy S. Morris Hayden G. Crossley Kay M. 7 2016
19 7 518 523 1440-2440 10.1016/j.jsams.2015.07.008 10.1016/j.jsams.2015.07.008 26205774
Anterior knee pain following anterior cruciate ligament reconstruction does not increase the risk of patellofemoral osteoarthritis at 15- and 20-year follow-ups Osteoarthritis and Cartilage Culvenor A.G. Øiestad B.E. Holm I. Gunderson R.B. Crossley K.M. Risberg M.A. 1 2017
25 1 30 33 1063-4584 10.1016/j.joca.2016.09.012 10.1016/j.joca.2016.09.012
A randomized comparison of patellar tendon and hamstring tendon anterior cruciate ligament reconstruction The American Journal of Sports Medicine Feller Julian A. Webster Kate E. SAGE Publications 7 2003
31 4 564 573 0363-5465 10.1177/03635465030310041501 10.1177/03635465030310041501 12860546
Plyometric training and drills Physical Rehabilitation of the Injured Athlete Cuoco Anthony Tyler Timothy F. Andrews J.R. Harrelson G.L. Wilk K.E. Elsevier Philadelphia, PA 2012
571 595 9781437724110 10.1016/b978-1-4377-2411-0.00026-5
Plyometric exercise in rehabilitation Rehabilitation Techniques in Sports Medicine Voight M. Tippett S. Prentice W.B. St. Louis, MO
Plyometrics Eccentric Muscle Training in Sports and Orthopedics Voight M. Draovitch P. Abert M. Churchill Livingstone New York 1991
45
Literature review: Explosive/plyometric exercise National Strength & Conditioning Association Journal Wathen D. 1993
15 3 17 18 0744-0049 10.1519/0744-0049(1993)015 10.1519/0744-0049(1993)015
The ten task-based progressions in rehabilitation after acl reconstruction: from post-surgery to return to play – a clinical commentary International Journal of Sports Physical Therapy Buckthorpe Matthew Tamisari Antonio Villa Francesco Della 5 2020
15 4 1 13 2159-2896 10.26603/ijspt20200611 10.26603/ijspt20200611 32089953
Quadriceps strength asymmetry following ACL reconstruction alters knee joint biomechanics and functional performance at time of return to activity The American Journal of Sports Medicine Palmieri-Smith Riann M. Lepley Lindsey K. 16 4 2015
43 7 1662 1669 0363-5465 10.1177/0363546515578252 10.1177/0363546515578252 25883169
Quadriceps and hamstring strength recovery during early neuromuscular rehabilitation after ACL hamstring-tendon autograft reconstruction J Sport Rehabil Harput Gulcan Kilinc H. Erkan Ozer Hamza Baltaci Gul Mattacola Carl G. 11 2015
24 4 398 404 1056-6716 10.1123/jsr.2014-0224 10.1123/jsr.2014-0224
Criteria for return to running after anterior cruciate ligament reconstruction: A scoping review British Journal of Sports Medicine Rambaud Alexandre J M Ardern Clare L Thoreux Patricia Regnaux Jean-Philippe Edouard Pascal BMJ 2 5 2018
52 22 1437 1434 0306-3674 10.1136/bjsports-2017-098602 10.1136/bjsports-2017-098602
Muscle strength and hop performance criteria prior to return to sports after ACL reconstruction Knee Surgery, Sports Traumatology, Arthroscopy Thomeé Roland Kaplan Yonatan Kvist Joanna Myklebust Grethe Risberg May Arna Theisen Daniel Tsepis Elias Werner Suzanne Wondrasch Barbara Witvrouw Erik Springer Science and Business Media LLC 20 9 2011
19 11 1798 1805 0942-2056 10.1007/s00167-011-1669-8 10.1007/s00167-011-1669-8
Key properties of expert movement systems in sport: An ecological dynamics perspective Sports Medicine Seifert Ludovic Button Chris Davids Keith Springer Science and Business Media LLC 2013
43 3 167 178 0112-1642 10.1007/s40279-012-0011-z 10.1007/s40279-012-0011-z 23329604
Task-based rehabilitation protocol for elite athletes following anterior cruciate ligament reconstruction: a clinical commentary Physical Therapy in Sport Herrington Lee Myer Gregory Horsley Ian 11 2013
14 4 188 198 1466-853X 10.1016/j.ptsp.2013.08.001 10.1016/j.ptsp.2013.08.001
On-field rehabilitation part 2: A 5-stage program for the soccer player focused on linear movements, multidirectional movements, soccer-specific skills, soccer-specific movements, and modified practice Journal of Orthopaedic & Sports Physical Therapy Buckthorpe Matthew Della Villa Francesco Della Villa Stefano Roi Giulio Sergio Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 8 2019
49 8 570 575 0190-6011 10.2519/jospt.2019.8952 10.2519/jospt.2019.8952 31291556
Muscle soreness, swelling, stiffness and strength loss after intense eccentric exercise. British Journal of Sports Medicine Cleak M J Eston R G 1 12 1992
26 4 267 271 0306-3674 10.1136/bjsm.26.4.267 10.1136/bjsm.26.4.267 1490222
Treatment and prevention of delayed onset muscle soreness J Strength Cond Res Connolly D.A.J. Sayers S.P. McHugh M.P. 2003
17 197 208 12580677
Metabolic consequences of exercise-induced muscle damage Sports Medicine Tee Jason C Bosch Andrew N Lambert Mike I 2007
37 10 827 836 0112-1642 10.2165/00007256-200737100-00001 10.2165/00007256-200737100-00001 17887809
Evidence-based clinical practice update: Practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus British Journal of Sports Medicine van Melick Nicky van Cingel Robert E H Brooijmans Frans Neeter Camille van Tienen Tony Hullegie Wim Nijhuis-van der Sanden Maria W G BMJ 18 8 2016
50 24 1506 1515 0306-3674 10.1136/bjsports-2015-095898 10.1136/bjsports-2015-095898
Knee loading deficits during dynamic tasks in individuals following anterior cruciate ligament reconstruction Journal of Orthopaedic & Sports Physical Therapy Pratt Kristamarie A. Sigward Susan M. Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 6 2017
47 6 411 419 0190-6011 10.2519/jospt.2017.6912 10.2519/jospt.2017.6912 28499343
Bilateral kinematic and kinetic analysis of the squat exercise after anterior cruciate ligament reconstruction Archives of Physical Medicine and Rehabilitation Salem George J Salinas Ruben Harding F.Victor 8 2003
84 8 1211 1216 0003-9993 10.1016/s0003-9993(03)00034-0 10.1016/s0003-9993(03)00034-0 12917862
Compensatory strategies that reduce knee extensor demand during a bilateral squat change from 3 to 5 months following anterior cruciate ligament reconstruction Journal of Orthopaedic & Sports Physical Therapy Sigward Susan M. Chan Ming-Sheng M. Lin Paige E. Almansouri Sara Y. Pratt Kristamarie A. Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 9 2018
48 9 713 718 0190-6011 10.2519/jospt.2018.7977 10.2519/jospt.2018.7977 29895231
Onfield rehabilitation part 1: 4 pillars of high-quality on-field rehabilitation are restoring movement quality, physical conditioning, restoring sport-specific skills, and progressively developing chronic training load Journal of Orthopaedic & Sports Physical Therapy Buckthorpe Matthew Della Villa Francesco Della Villa Stefano Roi Giulio Sergio 8 2019
49 8 565 569 0190-6011 10.2519/jospt.2019.8954 10.2519/jospt.2019.8954 31291553
