INSIGHTS AND INTERVENTIONS
– Written by Vasileios Sideris, Nuno Nascimento, Andreas Bjerregaard
INTRODUCTION
Following any knee injury or surgery, there is commonly a phase of reduced activity and disuse that leads to muscle atrophy1, diminished strength, and anterior knee pain2. After an anterior cruciate ligament (ACL) injury, patients might experience a decrease of 20% to 33% in their quadriceps muscle volume from the moment of injury up to three weeks post-ACL reconstruction (ACLR)2,3. The decline in muscle mass and strength can be a source of pain, functional limitation, and decreased physical fitness4. These persistent muscle weaknesses after surgery can result in functional deficits lasting up to 3 years postoperatively5. Periods of reduced mobility before and after surgery, vascular ischemia6, and inability to perform high load strength training preoperatively and in the early postoperative period contribute to these early losses7.
An extensive amount of research after ACLR indicates that a significant proportion of patients fall short of meeting adequate levels of strength, function and performance as recommended at the time of return to sport (RTS)8,9. Approximately 35% of athletes fail to return to sport (RTS) at their preinjury level10 and are at a high risk of reinjury in the 24 months after RTS11. The long term health and future injury risk of the operated knee might be reduced if they meet established discharge criteria12 or achieve strength symmetry13.
With the ultimate objective of regaining or even surpassing the patient's previous level of performance and protecting them from future injuries in mind, the rehabilitation team must guide the patient through an extensive recovery journey and adeptly devise interventions. These interventions are aimed at rectifying deficits in strength and functional performance by precisely targeting the underlying mechanisms that result in muscle atrophy and impaired neuromuscular activation.
STRENGTH DEFICITS
The exact mechanisms leading to quadriceps weakness remain unclear; however, neurological and morphological changes that have been observed are considered the primary factors contributing to the decline in knee extensors strength14. The following sections will outline some of these mechanisms and propose potential interventions aimed at enhancing neuromuscular function.
NEUROLOGICAL FACTORS
As a direct consequence of trauma to the knee, some patients develop substantial neuromuscular impairments of the quadriceps muscle, known as arthrogenic muscle inhibition (AMI)15. Joint swelling, inflammation, pain and structural damage that occur after knee injury or knee surgery are the major drivers of this process. They contribute to the disturbance of the sensory system and the modification of proprioceptive input from the knee joint, triggering reflex responses that result in decreased excitability of motor neurons supplying the quadriceps and hamstrings.
Furthermore, the immediate neural adaptations within the nervous system resulting from an ACL injury can lead reductions in muscle fiber conduction velocity and spontaneous fiber discharge which are indirect markers of denervated fibers in the muscle groups surrounding the knee16. This disruption in neural pathways can decrease the muscle's capability for contraction, making it challenging to activate the muscle during exercise and the subsequent development of weakness17.
Identifying and minimizing AMI early in rehabilitation is vital to optimize strength development throughout the rehab process. Without addressing AMI with targeted interventions, patients may struggle to perform exercises effectively, leading to compensatory movement patterns and persistent strength deficits.
MUSCLE MORPHOLOGY
Morphological factors such as fiber type composition and muscle architecture influence the size and contractile capacity of the muscle18. In a study investigating which factors determine maximum isometric knee torque, Trezise et al19 found muscle size (cross sectional area of the quadriceps) as well as fascicle length were the strongest predictors explaining approximately 50% and about 20% of the variability respectively.
It has been reported that patients who have undergone ACLR, demonstrate decreased quadriceps muscle volume and cross-sectional area20. There are observed selective reductions in type IIA (fast oxidative glycolytic) muscle fibers cross-sectional area and frequency21. While these changes can only partially explain the quadriceps weakness observed after ACLR, it is essential to emphasize these findings as it will enhance our comprehension of the issue.
It is important to highlight that the muscle atrophy seen following a traumatic joint injury like an ACL rupture, differs in its underlying causes from the muscle atrophy that results from disuse. In cases of traumatic joint injury, neurological changes appear to play a significant role in causing a rapid reduction in muscle mass17. Because the injury leads to a range of factors that contribute to muscle atrophy, traditional strength training approaches might not be effective if the underlying neurological changes are not addressed first. Instead, personalized interventions that are more targeted and adapted to the individual's morphological and neurological deficits are necessary.
TREATMENT MODALITIES AND EARLY PHASE INTERVENTIONS
In the Aspetar clinical practice guidelines on rehabilitation after ACLR22 a range of modalities have been proposed to enhance strength outcomes and promote muscle activation. In the following section we cover the practical aspect of neuromuscular electrical stimulation (NMES), Surface Electromyography (EMG) biofeedback and blood flow restriction (BFR).
NEUROMUSCULAR ELECTRICAL STIMULATION
NMES is a therapeutic modality commonly used to address muscle disuse atrophy after ACLR. Interventions utilizing NMES 4 to 6 weeks after ACLR have been shown to aid in the recovery of quadriceps strength and functional performance, outperforming rehabilitation without NMES22. Furthermore, recent studies underscore the advantages of promptly initiating NMES after ACL injury and subsequent surgery, as it effectively mitigates skeletal muscle atrophy and contractile dysfunction23. However, it is noteworthy that other ACLR-related studies have reported contrasting results, failing to demonstrate any advantage in postoperative strength attributable to NMES interventions implemented within similar temporal parameters24. The use of NMES is encouraged, starting as early as the second day of ACLR, unless contraindicated22,24.
According to the recently published Aspetar Clinical Practice Guideline on Rehabilitation after ACLR22, it is recommended to use NMES together with active functional exercises, as it provides superior results in restoring quadriceps strength and force symmetry when compared to NMES alone. Moreover, the literature suggests that the use of NMES after ACLR can lead to a significant reduction in knee joint swelling during the early phase of rehabilitation and a moderate reduction in the intermediate and advanced phases24. Some examples of exercises that we use at Aspetar during the early phase are together with NMES are: isometric quadriceps at different angles of knee flexion, static quads contraction, straight leg raise, isometric open kinetic chain exercises in various degrees of knee extension, and isometric wall squat.
Regarding volume, the literature suggests a frequency from 2-5 times per week to daily24. Considering that the use of NMES is safe even in the early stages of ACLR rehabilitation, at Aspetar we use it every session, preferably during warm-up, reaching the maximum tolerable intensity by the patient, aiming for a minimum of 100mA within 6 weeks after the surgery, for 20 minutes with the electrodes being placed proximal and distal to the targeted muscle (quadriceps for BPTB and QT grafts; Quadriceps and Hamstrings for HT graft).
The use of NMES may offer its most pronounced benefits during the early stages of recovery, gradually diminishing in effectiveness as patients regain strength and the ability for voluntary muscle activation improves25. A summary of Aspetar’s NMES recommendations (frequency, dosage, intensity, electrode placement, muscle groups and goals) can be found in the Modalities Table (Table 1).
EMG BIOFEEDBACK
Surface electromyography serves as a valuable modality utilized by both clinicians and researchers to investigate human motion. Its primary purpose is to gain insights into the intricate process through which our nervous system manages our movements by orchestrating the complex patterns of muscle activation and deactivation. With modern technology, these muscle action patterns can be turned into visual or auditory signals that can be observed by the clinicians and be used as feedback by their patients.
It has been shown that patients with ACLR display an altered muscle activity pattern during jumping and cutting/change-of-direction tasks27,28, even though they are capable to return to sport29. This is also seen in functional tasks like running where ACLR patients show neuromuscular alterations during different phases of running with a reduced medial hamstring activity in stance phase30. Altered EMG muscle signals have been found in relation to the contralateral limb and between first time ACLR and secondary ACLR31. These changes might have implications for the return to sport as the patient develops a more long-term protective mechanism to minimize knee loads32.
Within the scope of ACL rehabilitation, EMG biofeedback interventions have three primary objectives: addressing muscle hypoactivity, muscle hyperactivity, and employing a combined approach focused on coordination training. Improved motor learning is an additional benefit achieved by providing external visual feedback of effort as the athlete works to determine the most effective strategy. As an illustration, one method to enhance quadriceps engagement involves instructing the patient to increase EMG amplitude to reach a specified threshold on the display, while hamstring relaxation is encouraged by maintaining EMG activity below a designated target marker.
While the evidence supporting the effectiveness of EMG biofeedback in improving active knee extension and quadriceps strength33 is currently limited, it does show promise. Additional research is necessary to establish precise clinical practice recommendations. However, it is important to note that EMG biofeedback is a safe, low cost and non-invasive intervention. It can be seamlessly integrated into standard rehabilitation protocols during regular activation and strengthening exercises or motor learning sessions.
We recommend the implementation of EMG biofeedback in each session during the early phase of ACLR rehabilitation. Emphasis should be placed on activating the inhibited muscles, while addressing muscle hyperactivity. Additionally, real-time biofeedback can be utilized during functional tasks such as single-leg stance/squat, with a focus on targeting knee extensors or flexors. The goal of the intervention is for the patient to increase their maximum EMG amplitude during each session.
BLOOD FLOW RESTRICTION TRAINING
BFR training has been shown to have beneficial effects addressing muscle atrophy after ACLR34. The primary use case is to improve muscle growth, muscle strength, and improve overall clinical outcomes35. During BFR, a cuff is placed proximally on the leg of the affected side. The cuff is inflated to a set pressure which will restrict the arterial inflow (the oxygenated blood flowing to the muscle) and minimize the venous return (the deoxygenated blood flowing from the muscle)36, fostering an anaerobic setting. This environment facilitates muscle growth through enhanced cell signaling, increased protein creation, and stimulated myogenic proliferation37.
BFR combined with low load resistance training (20%–30% 1RM) has shown better results in increasing muscle volume and strength after ACLR, when compared to isolated low load resistance training and similar to high load resistance training2,38. In the early phase after ACLR, where the patient can be load-compromised by having restrictions with limited range of motion, weight bearing, and/or swelling and pain.", traditional heavy strength training may not be feasible2. BFR training can offer an effective alternative solution to achieve some of the same responses as heavier progressive strength training while minimizing the mechanical load of the knee joint4,39,40.
In the existing literature, there is considerable variability concerning the frequency, volume, cuff width and limb occlusion pressure (LOP) of BFR training41. An extensive review of methodologies2, recommended BFR with a frequency of 2-3 session per week when interventions lasting longer than three weeks or 1-2 session per day when lasting less than three weeks3,36. When applying BFR, a submaximal percentage (40%-80%) of total LOP is desired. This method allows for appropriate progression of the pressure, similar to progressive loading resistance training42. A common LOP used as starting point is usually above 200mmhg, and from this point the pressure is gradually reduced to achieve a 40-80% occlusion. BFR is a method to facilitate getting the muscle to fatigue or “chasing the pump”, which can effectively be achieved at several percentage levels of LOP. Personalized LOP’s have been suggested to be more efficient in achieving optimal clinical outcomes in a safer manner43.
Our recommendations are to start with BFR as soon as possible after ACLR, with a minimum of 2 to 3 times per week for a block of 8 to 14 weeks. Our protocol for isolated muscles consists of 4 sets of 30-15-15-15 repetitions (20-30% of 1RM) aiming for a LOP of 80%, if possible2,36,44-47. Another practical way to apply BFR is to use it during warm-up/cardio exercises such as elliptical trainer, walking or cycling. In cycling, we encourage our patient to keep a pace of 90-100 RPM. Furthermore, BFR could also be used to target desired muscle groups or as a session “finisher” to stress muscle fibers that may have not been sufficiently stressed during the training session.
When applying BFR, some precautions must be taken into consideration as most studies have stringent inclusion/exclusion criteria, leaving limited data on individuals with comorbidities frequently seen in rehabilitation clinics32. Delayed onset muscle soreness (DOMS) is one of the most reported symptoms after BFR48, and the one we are looking for in our targeted muscles. Numbness is another commonly reported symptom after BFR, probably due to inappropriately high tourniquet pressures, thus resulting in peripheral nerve compression49. Therefore, appropriate selection and application of the cuff (size, site, pressure) is essential for preventing peripheral nerve irritation34. A ‘traffic light’ approach is suggested to screen the patient for eligibility for BFR (Figure 4).
CLINICAL CASE STUDIES
Case 1
A 25-year-old soccer player presented with anterior knee pain and severe quadriceps weakness three-months post ACLR and patella repair. The patient was unable to follow the regular rehabilitation routine because exercises aimed at strengthening the muscles were causing pain, leading to a fear of movement.
During isometric knee extension strength testing, it was found that there was a 50% asymmetry in the strength of the knee extensor muscles. Additionally, the patient exhibited a compensatory movement pattern during a double-leg squat, exhibiting 30% higher ground reaction force on the non-injured side. He also had difficulty squatting beyond 60-degrees knee flexion during single leg squat and showed 40% higher impact force during a step-down test indicating lack of eccentric control during the task.
For the initial assessment, EMG sensors were applied over vastus medialis (VMO), vastus lateralis (VL), and rectus femoris (RF) muscles and asked the patient to perform regular exercises such as straight leg raises, double leg squat, isometric contractions at various knee flexion angles. A significantly reduced activation of VMO muscle was observed during the test.
Our team utilized EMG feedback cues to enhance the activity of the VMO and improve the ratio of VMO to VL activation. Due to the motor learning benefits of EMG biofeedback, within the initial session observable improvements were evident with the patient succeeded in activating his VMO during exercises that had previously no/minimal activation during testing.
Following the initial assessment, we integrated EMG biofeedback into the patient's rehabilitation sessions, with a primary focus on enhancing quadriceps activation, particularly emphasizing the VMO. In addition to EMG, the patient started every session with NMES to facilitate quadriceps activation followed by 10 minutes bicycle using BFR. During the session, leg extension with BFR protocol consisting of 30-15-15-15 reps was added. Over a two-week period consisting of six sessions, the patient experienced a notable reduction in pain and was able to execute open chain quadriceps strengthening and compound exercises without symptoms facilitating the opportunity to increase the strength training stimulus and adaptation. He also reported a much-improved sensation of quadriceps activity and muscular exertion with observable normalized activation patterns compared to the contralateral limb. These sessions seemed to instill in the patient a sense of empowerment and confidence, eventually enabling him to achieve the strength and functional criteria to progress to the advanced phase of his rehabilitation program.
Case 2
A 28-year-old professional football player, 3 months post-ACLR (hamstring graft), experiencing significant difficulty activating medial hamstrings during his rehabilitation. The athlete faced a challenge, as his rehabilitation was hampered by persistent pain and weakness in the medial hamstrings, hindering the execution of conventional strengthening exercises and functional training. He displayed an apparent avoidance behavior during hamstring strength testing, exhibiting a 45% strength deficit compared to the uninjured limb.
Recognizing the need for a more comprehensive evaluation and intervention, the athlete was brought into our specialized Assessment and Movement Analysis Lab (AMAL). Here, we employed the advanced EMG system, which provided feedback on co-contraction and activation patterns of lower limb muscles. This evaluation revealed significantly reduced EMG activity on the medial hamstrings and helped identifying patterns and exercises that specifically enhance medial hamstring activation, decrease lateral hamstring hyperactivity, and promote the patient’s motor-control learning process. Remarkably, after a single session, the athlete demonstrated the ability to retain and apply the enhanced activation patterns. Transitioning back to the clinic, his rehabilitation program involved a portable 2-channel EMG device used daily, incorporating engaging exercises and "games" to promote muscle activation.
In tandem with the EMG advancements, we integrated NMES and BFR interventions following Aspetar protocols. The NMES, offered direct stimulation to the hamstring muscles, promoting increased muscle activation together with active exercises.
BFR, executed according to Aspetar's protocol, was introduced during low-intensity resistance and isometric exercises. This integration induced muscle hypertrophy and strength gains at reduced exercise intensities, as evidenced by the enhanced muscle pump and metabolic stress.
Over a meticulously planned 6-week block, the athlete made significant strides in his rehabilitation. The combination of advanced EMG technology, and the NMES and BFR protocols, helped the patient to increase his medial hamstring activity and reduce his strength deficit to 20%. The athlete reported a significant reduction in pain and a renewed confidence in his hamstring’s capacity - a critical advancement for the dynamic and explosive movements integral to football.
This case exemplifies the intricate and multidimensional approach required for a holistic post-ACLR rehabilitation. The focused attention beyond the customary emphasis on the quadriceps, unveils a comprehensive pathway for athletes and clinicians navigating the complex landscape of post-ACLR rehabilitation.
SUMMARY
The utilization of modalities such as NMES, EMG and BFR presents promising avenues for enhancing knee muscle function subsequent to ACLR. During the initial stages of rehabilitation, NMES can minimize muscle atrophy and contractile dysfunction. EMG provides valuable biofeedback enabling patients to acquire essential muscle control skills and enhance quadriceps engagement. BFR offers a solution for promoting muscle growth, particularly in scenarios where compromised knee load-bearing due to restricted range of motion or weight-bearing limitations, or hindered muscle activation caused by AMI is a concern. By embracing these modalities, muscle function (in particular the quadriceps and hamstrings) can be optimized in the early stages of rehabilitation setting a solid platform for progression to more traditional strength training strategies in the later phases optimizing knee function and successful recovery following ACLR.
Vasileios Sideris PT
Senior Biomechanist
Nuno Nascimento PT
Physiotherapist
Andreas Bjerregaard PT
Physiotherapist
Aspetar Orthopedic and Sports Medicine Hospital
Doha,Qatar
Contact: vasileios.sideris@aspetar.com
References
1. Breen L, Stokes KA, Churchward-Venne TA, et al. Two weeks of reduced activity decreases leg lean mass and induces "anabolic resistance" of myofibrillar protein synthesis in healthy elderly. J Clin Endocrinol Metab 2013;98(6):2604-12. doi: 10.1210/jc.2013-1502 [published Online First: 2013/04/17]
2. Caetano D, Oliveira C, Correia C, et al. Rehabilitation outcomes and parameters of blood flow restriction training in ACL injury: A scoping review. Physical Therapy in Sport 2021;49:129-37. doi: https://doi.org/10.1016/j.ptsp.2021.01.015
3. Wengle L, Migliorini F, Leroux T, et al. The Effects of Blood Flow Restriction in Patients Undergoing Knee Surgery: A Systematic Review and Meta-analysis. The American Journal of Sports Medicine 2021;50(10):2824-33. doi: 10.1177/03635465211027296
4. Hughes L, Paton B, Rosenblatt B, et al. Blood flow restriction training in clinical musculoskeletal rehabilitation: a systematic review and meta-analysis. Br J Sports Med 2017;51(13):1003-11. doi: 10.1136/bjsports-2016-097071 [published Online First: 2017/03/06]
5. Meier WA, Marcus RL, Dibble LE, et al. The long-term contribution of muscle activation and muscle size to quadriceps weakness following total knee arthroplasty. J Geriatr Phys Ther 2009;32(2):79-82. [published Online First: 2009/12/31]
6. Daniel DM, Lumkong G, Stone ML, et al. Effects of tourniquet use in anterior cruciate ligament reconstruction. Arthroscopy 1995;11(3):307-11. doi: 10.1016/0749-8063(95)90008-x [published Online First: 1995/06/01]
7. Hughes L, Patterson SD, Haddad F, et al. Examination of the comfort and pain experienced with blood flow restriction training during post-surgery rehabilitation of anterior cruciate ligament reconstruction patients: A UK National Health Service trial. Physical Therapy in Sport 2019;39:90-98. doi: https://doi.org/10.1016/j.ptsp.2019.06.014
8. Toole AR, Ithurburn MP, Rauh MJ, et al. Young Athletes Cleared for Sports Participation After Anterior Cruciate Ligament Reconstruction: How Many Actually Meet Recommended Return-to-Sport Criterion Cutoffs? J Orthop Sports Phys Ther 2017;47(11):825-33. doi: 10.2519/jospt.2017.7227 [published Online First: 2017/10/11]
9. Webster KE, Hewett TE. What is the Evidence for and Validity of Return-to-Sport Testing after Anterior Cruciate Ligament Reconstruction Surgery? A Systematic Review and Meta-Analysis. Sports medicine (Auckland, NZ) 2019;49(6):917-29. doi: 10.1007/s40279-019-01093-x
10. Clare LA, Nicholas FT, Julian AF, et al. Fifty-five per cent return to competitive sport following anterior cruciate ligament reconstruction surgery: an updated systematic review and meta-analysis including aspects of physical functioning and contextual factors. British Journal of Sports Medicine 2014;48(21):1543. doi: 10.1136/bjsports-2013-093398
11. Paterno MV, Rauh MJ, Schmitt LC, et al. Incidence of Second ACL Injuries 2 Years After Primary ACL Reconstruction and Return to Sport. Am J Sports Med 2014;42(7):1567-73. doi: 10.1177/0363546514530088 [published Online First: 2014/04/23]
12. Kyritsis P, Bahr R, Landreau P, et al. Likelihood of ACL graft rupture: not meeting six clinical discharge criteria before return to sport is associated with a four times greater risk of rupture. Br J Sports Med 2016;50(15):946-51. doi: 10.1136/bjsports-2015-095908 [published Online First: 2016/05/25]
13. Hege G, Lynn S-M, Håvard M, et al. Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. British Journal of Sports Medicine 2016;50(13):804. doi: 10.1136/bjsports-2016-096031
14. Palmieri-Smith RM, Thomas AC, Wojtys EM. Maximizing quadriceps strength after ACL reconstruction. Clin Sports Med 2008;27(3):405-24, vii-ix. doi: 10.1016/j.csm.2008.02.001 [published Online First: 2008/05/28]
15. Nuccio S, Del Vecchio A, Casolo A, et al. Deficit in knee extension strength following anterior cruciate ligament reconstruction is explained by a reduced neural drive to the vasti muscles. The Journal of physiology 2021;599(22):5103-20. doi: 10.1113/jp282014 [published Online First: 2021/10/05]
16. Fry CS, Johnson DL, Ireland ML, et al. ACL injury reduces satellite cell abundance and promotes fibrogenic cell expansion within skeletal muscle. J Orthop Res 2017;35(9):1876-85. doi: 10.1002/jor.23502 [published Online First: 2016/12/10]
17. Lepley LK, Davi SM, Burland JP, et al. Muscle Atrophy After ACL Injury: Implications for Clinical Practice. Sports Health 2020;12(6):579-86. doi: 10.1177/1941738120944256 [published Online First: 2020/09/01]
18. Cormie P, McGuigan MR, Newton RU. Developing maximal neuromuscular power: Part 1--biological basis of maximal power production. Sports Med 2011;41(1):17-38. doi: 10.2165/11537690-000000000-00000 [published Online First: 2010/12/15]
19. Trezise J, Collier N, Blazevich AJ. Anatomical and neuromuscular variables strongly predict maximum knee extension torque in healthy men. Eur J Appl Physiol 2016;116(6):1159-77. doi: 10.1007/s00421-016-3352-8 [published Online First: 2016/04/15]
20. Birchmeier T, Lisee C, Kane K, et al. Quadriceps Muscle Size Following ACL Injury and Reconstruction: A Systematic Review. J Orthop Res 2020;38(3):598-608. doi: 10.1002/jor.24489 [published Online First: 2019/10/15]
21. Noehren B, Andersen A, Hardy P, et al. Cellular and Morphological Alterations in the Vastus Lateralis Muscle as the Result of ACL Injury and Reconstruction. The Journal of bone and joint surgery American volume 2016;98(18):1541-7. doi: 10.2106/jbjs.16.00035 [published Online First: 2016/09/23]
22. Kotsifaki R, Korakakis V, King E, et al. Aspetar clinical practice guideline on rehabilitation after anterior cruciate ligament reconstruction. Br J Sports Med 2023;57(9):500-14. doi: 10.1136/bjsports-2022-106158 [published Online First: 2023/02/03]
23. Natsume T, Ozaki H, Kakigi R, et al. Effects of training intensity in electromyostimulation on human skeletal muscle. Eur J Appl Physiol 2018;118(7):1339-47. doi: 10.1007/s00421-018-3866-3 [published Online First: 2018/04/22]
24. Conley CEW, Mattacola CG, Jochimsen KN, et al. A Comparison of Neuromuscular Electrical Stimulation Parameters for Postoperative Quadriceps Strength in Patients After Knee Surgery: A Systematic Review. Sports Health 2021;13(2):116-27. doi: 10.1177/1941738120964817 [published Online First: 2021/01/12]
25. Norte G, Rush J, Sherman D. Arthrogenic Muscle Inhibition: Best Evidence, Mechanisms, and Theory for Treating the Unseen in Clinical Rehabilitation. J Sport Rehabil 2022;31(6):717-35. doi: 10.1123/jsr.2021-0139 [published Online First: 2021/12/10]
26. Maffiuletti NA. Physiological and methodological considerations for the use of neuromuscular electrical stimulation. Eur J Appl Physiol 2010;110(2):223-34. doi: 10.1007/s00421-010-1502-y [published Online First: 2010/05/18]
27. Burland JP, Lepley AS, Frechette L, et al. Protracted alterations in muscle activation strategies and knee mechanics in patients after Anterior Cruciate Ligament Reconstruction. Knee Surg Sports Traumatol Arthrosc 2020;28(12):3766-72. doi: 10.1007/s00167-019-05833-4 [published Online First: 2020/01/04]
28. Sherman DA, Glaviano NR, Norte GE. Hamstrings Neuromuscular Function After Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-Analysis. Sports Med 2021;51(8):1751-69. doi: 10.1007/s40279-021-01433-w [published Online First: 2021/02/21]
29. Georgoulis JD, Melissaridou D, Patras K, et al. Neuromuscular activity of the lower-extremities during running, landing and changing-of-direction movements in individuals with anterior cruciate ligament reconstruction: a review of electromyographic studies. J Exp Orthop 2023;10(1):43. doi: 10.1186/s40634-023-00603-1 [published Online First: 2023/04/15]
30. Einarsson E, Thomson A, Sas B, et al. Lower medial hamstring activity after ACL reconstruction during running: a cross-sectional study. BMJ Open Sport Exerc Med 2021;7(1):e000875. doi: 10.1136/bmjsem-2020-000875 [published Online First: 2021/03/31]
31. Palmieri-Smith RM, Strickland M, Lepley LK. Hamstring Muscle Activity After Primary Anterior Cruciate Ligament Reconstruction-A Protective Mechanism in Those Who Do Not Sustain a Secondary Injury? A Preliminary Study. Sports Health 2019;11(4):316-23. doi: 10.1177/1941738119852630 [published Online First: 2019/06/14]
32. Nyland J, Klein S, Caborn DN. Lower extremity compensatory neuromuscular and biomechanical adaptations 2 to 11 years after anterior cruciate ligament reconstruction. Arthroscopy 2010;26(9):1212-25. doi: 10.1016/j.arthro.2010.01.003 [published Online First: 2010/09/03]
33. !!! INVALID CITATION !!! 51-54
34. DePhillipo NN, Kennedy MI, Aman ZS, et al. Blood Flow Restriction Therapy After Knee Surgery: Indications, Safety Considerations, and Postoperative Protocol. Arthrosc Tech 2018;7(10):e1037-e43. doi: 10.1016/j.eats.2018.06.010 [published Online First: 2018/11/01]
35. Wengle L, Migliorini F, Leroux T, et al. The Effects of Blood Flow Restriction in Patients Undergoing Knee Surgery: A Systematic Review and Meta-analysis. Am J Sports Med 2022;50(10):2824-33. doi: 10.1177/03635465211027296 [published Online First: 2021/08/19]
36. Patterson SD, Hughes L, Warmington S, et al. Blood Flow Restriction Exercise: Considerations of Methodology, Application, and Safety. Frontiers in physiology 2019;10:533. doi: 10.3389/fphys.2019.00533 [published Online First: 2019/06/04]
37. Nielsen JL, Aagaard P, Bech RD, et al. Proliferation of myogenic stem cells in human skeletal muscle in response to low-load resistance training with blood flow restriction. The Journal of physiology 2012;590(17):4351-61. doi: 10.1113/jphysiol.2012.237008 [published Online First: 2012/07/18]
38. Loenneke JP, Wilson JM, Marín PJ, et al. Low intensity blood flow restriction training: a meta-analysis. Eur J Appl Physiol 2012;112(5):1849-59. doi: 10.1007/s00421-011-2167-x [published Online First: 2011/09/17]
39. Rolnick N, Schoenfeld BJ. Blood Flow Restriction Training and the Physique Athlete: A Practical Research-Based Guide to Maximizing Muscle Size. Strength & Conditioning Journal 2020;42(5)
40. Scott BR, Loenneke JP, Slattery KM, et al. Blood flow restricted exercise for athletes: A review of available evidence. J Sci Med Sport 2016;19(5):360-7. doi: 10.1016/j.jsams.2015.04.014 [published Online First: 2015/06/30]
41. Mattocks KT, Jessee MB, Mouser JG, et al. The Application of Blood Flow Restriction: Lessons From the Laboratory. Curr Sports Med Rep 2018;17(4):129-34. doi: 10.1249/jsr.0000000000000473 [published Online First: 2018/04/10]
42. Bond CW, Hackney KJ, Brown SL, et al. Blood Flow Restriction Resistance Exercise as a Rehabilitation Modality Following Orthopaedic Surgery: A Review of Venous Thromboembolism Risk. J Orthop Sports Phys Ther 2019;49(1):17-27. doi: 10.2519/jospt.2019.8375 [published Online First: 2018/09/14]
43. McEwen JA, Owens JG, Jeyasurya J. Why is it Crucial to Use Personalized Occlusion Pressures in Blood Flow Restriction (BFR) Rehabilitation? Journal of Medical and Biological Engineering 2019;39(2):173-77. doi: 10.1007/s40846-018-0397-7
44. Jack RA, 2nd, Lambert BS, Hedt CA, et al. Blood Flow Restriction Therapy Preserves Lower Extremity Bone and Muscle Mass After ACL Reconstruction. Sports Health 2023;15(3):361-71. doi: 10.1177/19417381221101006 [published Online First: 2022/06/29]
45. Ohta H, Kurosawa H, Ikeda H, et al. Low-load resistance muscular training with moderate restriction of blood flow after anterior cruciate ligament reconstruction. Acta Orthop Scand 2003;74(1):62-8. doi: 10.1080/00016470310013680 [published Online First: 2003/03/15]
46. Prue J, Roman DP, Giampetruzzi NG, et al. Side Effects and Patient Tolerance with the Use of Blood Flow Restriction Training after ACL Reconstruction in Adolescents: A Pilot Study. Int J Sports Phys Ther 2022;17(3):347-54. doi: 10.26603/001c.32479 [published Online First: 2022/04/09]
47. Nascimento DDC, Rolnick N, Neto IVS, et al. A Useful Blood Flow Restriction Training Risk Stratification for Exercise and Rehabilitation. Frontiers in physiology 2022;13:808622. doi: 10.3389/fphys.2022.808622 [published Online First: 2022/04/02]
48. de Queiros VS, Dos Santos Í K, Almeida-Neto PF, et al. Effect of resistance training with blood flow restriction on muscle damage markers in adults: A systematic review. PLoS One 2021;16(6):e0253521. doi: 10.1371/journal.pone.0253521 [published Online First: 2021/06/19]
49. Vanwye WR, Weatherholt AM, Mikesky AE. Blood Flow Restriction Training: Implementation into Clinical Practice. Int J Exerc Sci 2017;10(5):649-54. [published Online First: 2017/10/03]
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