Quadriceps weakness often persists as a robust finding in patients with knee pain. This is true in overuse type injuries such as patellofemoral pain syndrome (Willy, 2019) and especially after knee surgeries like anterior cruciate ligament repair (ACL-R) (Baron, 2020; Current Concepts, 2016; Thomas, 2016; Logerstedt, 2017), and total knee arthroplasty (TKA, i.e., knee preplacement surgery; Christensen, 2018). Quadriceps weakness can produce dysfunction in walking gait, functional mobility, and of course limit the ability to maximize athletic performance or safe return to sport.
So, it is no surprise that quadriceps (quad) muscle strengthening is a common focus of many post-operative rehabilitation programs and also used as a treatment for knee pain that is managed non-surgically. Especially in patients following ACL reconstruction, the importance of developing quad muscle strength and power to facilitate recovery and return to sports cannot be understated.
The most current clinical practice guideline for knee ligament injuries recommends using open and closed kinetic chain exercises within 4-6 weeks after ACL reconstruction surgery and doing so 2-3 times per week for 6-10 months (Logerstedt, 2017; based on Grade A, highest level evidence). Use of Neuromuscular Electrical Stimulation (NMES) is also recommended to facilitate quadriceps strengthening in ACL post-operative patients, and recommendations advise using this for 6-8weeks for best outcomes (Logerstedt, 2017)
Clinical practice guidelines for patellofemoral pain similarly recommend quad muscle strengthening in open and closed chain movements (and hip muscle strengthening) with a high level of evidence (Willy, 2019; Grade A Evidence).
So, what are the BEST exercise choices to strengthen the quadriceps muscles?
First, I thought it would be helpful to list some commonly used exercises for quad muscle strengthening:
Open Kinetic Chain
- Short Arc Quad
- Long Arc Quad
Straight Leg Raises (SLR):
- Long sitting
- “Quad Sets”
- Isometrics on knee extension machine
Closed Kinetic Chain
- Double leg
- Single leg
- Moving platform
- Shuttle press
- Forward Step Up
- Lateral Step up
- Heel Taps
- Step Downs
- Double leg
- Single leg
I tend to select exercises for my patients in physical therapy based on these 3 Principles:
- Protect Healing Tissues
- Tailor to Individual Goals
- Build Capacity
1-Protect Healing Tissues
Protecting healing tissues is most obvious and crucial right after an acute or traumatic injury like a bone fracture, ligament tear, or joint dislocation. At the knee, most often we are protecting after a surgery like an ACL reconstruction, meniscus repair, or knee replacement (TKA). We could also be protecting tissues around the patellofemoral joint after a patellar dislocation or even after overuse injuries such as inflammation or irritation of the patellar retinaculum or fat pad in patellofemoral pain syndrome. Below are some brief thoughts on ways that quad exercises may be selected to protect healing tissues.
*NOTE: this is NOT meant to be a comprehensive list and NOT intended for medical advice. Surgical precautions will vary based on procedure and surgeon preference, please consult a healthcare provider for individual recommendations.
ACL Surgery Considerations
After ACL surgery, priority is placed on protecting the new ACL graft and also reducing stress on the patellofemoral joint and extensor mechanism (if patellar or quadriceps tendon graft) or hamstrings (if hamstring graft is used).
See below for some excellent recent discussions of quad strengthening after ACL-R surgery that are definitely worth a read or listen:
Two recent articles from JOSPT and IJSPT discussing considerations for when and why to use certain exercises for quadriceps muscle strengthening, including the pros and cons of open chain exercises. Key takeaways from these articles:
- Knee extensions are not necessarily “bad” to do after ACL surgery, but care must be taken to allow for graft healing and not be too aggressive with weight and volume of loading or full extension range of motion to early in rehabilitation (Protect Healing Tissues!)
- Avoiding the last 40° of extension in open kinetic chain knee extension can reduce strain on the ACL graft and also on the patellofemoral joint
- Early on in rehabilitation from ACL reconstruction surgery (before 6-9 months post operative), it is best to work at lower loads and in the range of 90-40° of knee flexion if performing open chain knee extension exercises
Also, two great podcast episodes featuring Eric Meira:
JOSPT Insights Episode #25:
JOSPT Insights Episode #28
Meniscus and Articular Cartilage Surgery Considerations
For a meniscus repair surgery or articular cartilage surgery (e.g, microfracture or cartilage replacement like OATs or MACI), there will likely be a need to protect the knee joint from compressive loads early on in the rehabilitation process (Logerstedt, 2018). Because of this, any exercises for quadriceps strength will likely need to be in open chain or non-weight bearing positions during this period (i.e., avoiding squats, lunges, leg press etc.). Further caution may be taken by limiting range of motion for loaded knee extension exercises as well to protect a healing meniscus or to protect a healing cartilage graft either at the tibiofemoral joint or patellofemoral joint.
Care can also be taken to further unload the medial or lateral meniscus by altering the position of the tibia in open chain exercises. For example, to take stress off of the medial meniscus, exercises such as short arc quads or straight leg raises could be performed with the tibia in internal rotation.
For patellar tendinopathy, loading for patients with high irritability usually begins with isometrics and progresses to heavier concentric and eccentric loading. For a more detailed discussion of exercise selection in tendinopathy rehabilitation, check out the posts below:
2-Tailor to Individual Goals
One art of physical therapy is selecting exercises that best serve to get patients back to the activities that they enjoy and value. For an athlete, this may mean selecting quad strength exercises in a variety of positions, speeds, loading schemes in order to provide the breadth necessary to have them return to running, jumping, or cutting sport. This may mean working on quad control in exercises like heavy split squats or lunge variations and at higher levels or end stage rehabilitation working on demanding exercises like drop landings or multidirectional plyometrics. For another individual, it may mean choosing eccentric type exercises for the quads to help them with functional movements like controlling descent in going down-stairs.
3- Build Capacity
Building capacity in this sense has to do with selecting exercises that will sufficiently challenge the quad’s ability to produce force and also has a lot to do with exercise “dosing” or volume of training. These parameters are more complex, but for a brief discussion of how to dose based on goals of training see this post:
One way to quantify how effective an exercise is to train a specific muscle or muscle group like the quads is to measure with electrodes the firing of muscles during that exercise. This is usually done with surface electrodes (sEMG), and a percentage of muscle firing is calculated based on a “maximum voluntary contraction” (MVIC). Muscle contraction and force production is clearly not this simplistic, but it does provide some information if used in comparing exercises or various muscle group firing patterns.
Some interesting research from EMG studies in healthy individuals show:
CLOSED KINETIC CHAIN QUAD STRENGTH EXERCISES:
- Higher quad muscle activation in squat variations vs. lunge and step up exercises:
- Muyor, 2020: Single leg squat had higher % quad EMG vs. forward lunge and lateral step up (all performed with weight for 5 repetitions)
- Navarro, 2020: Rear foot elevated split squat (Bulgarian split squat) had higher % quad EMG vs. lunge (both performed with weight for 5 repetitions)
- Closed kinetic chain exercise (vs. Open chain) had increased quad activation (and more uniform activation of all quad muscles) (Stensdotter, 2003)
OPEN KINETIC CHAIN EXERCISES:
- Higher Quad force production in SLR with Hip ER and active ankle DF (Mikaili, 2018)
What are your favorite quad exercises and why? I would love to hear your thoughts on quad exercise selection in rehabilitation settings. Please post in comments below and happy quad loading!
Current Concepts of Orthopaedic Physical Therapy 4th Ed.Orthopaedic Section, APTA, Inc.; 2016.
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Christensen JC, Mizner RL, Foreman KB, Marcus RL, Pelt CE, LaStayo PC. Quadriceps weakness preferentially predicts detrimental gait compensations among common impairments after total knee arthroplasty. J Orthop Res. 2018 Sep;36(9):2355-2363.
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Navarro, Enrique et al. Electromyographic activity of quadriceps and hamstrings of a professional football team during Bulgarian Squat and Lunge exercises. Journal of Human Sport and Exercise, 2020.
Noehren B, Snyder-Mackler L. Who’s Afraid of the Big Bad Wolf? Open-Chain Exercises After Anterior Cruciate Ligament Reconstruction. J Orthop Sports Phys Ther. 2020 Sep;50(9):473-475.
Thomas AC, Wojtys EM, Brandon C, Palmieri-Smith RM. Muscle atrophy contributes to quadriceps weakness after anterior cruciate ligament reconstruction. J Sci Med Sport. 2016 Jan;19(1):7-11.
Wilk KE, Arrigo CA, Bagwell MS, Finck AN. Considerations with Open Kinetic Chain Knee Extension Exercise Following ACL Reconstruction. IJSPT. 2021;16(1):282-284.
Willy RW, Hoglund LT, Barton CJ, et al. Patellofemoral Pain: Clinical Practice Guidelines Linked to the International Classification of Functioning, Disability and Health from the Academy of Orthopaedic Physical Therapy of the American Physical Therapy Association. J Orthop Sports Phys Ther. 2019;49(9):CPG1-CPG95.
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