The quadriceps is the muscle that decides, more than any other, how your knee is doing. It keeps the kneecap on track, brakes the body when you go down the stairs, and takes over part of the work of the ligaments when they are weak or injured. When it loses strength, after an operation, after weeks of pain or simply through a sedentary life, the knee notices quickly. If, however, the problem is not that it is weak but that it is sore and hard, before strengthening it it is worth understanding what lies behind that sensation: a tight quadriceps, what is really going on.
In this guide you will find the exercises for strengthening the quadriceps that I actually use with patients, divided by type, with sets and repetitions, and above all in the order in which they should be introduced. Because the most common mistake is not choosing the wrong exercise: it is choosing the right one too soon. You will also find, condition by condition, what the literature says and how solid it is.
Important, read this before continuing. The exercises and advice in this article are general guidance and may not be suitable for your situation. If your knee has had an operation or an injury, the programme should be built with the person following you.
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Why strengthening the quadriceps protects the knee
There are three reasons, and it is worth understanding them before you start: knowing what you are training changes the way you perform the exercise.
It stabilises the kneecap. The quadriceps guides the kneecap as it glides in its groove in the femur. When it is weak or fires late, the kneecap works crooked and the classic pain at the front of the knee appears, the kind that gets worse on stairs, when squatting or after sitting for a long time with your legs bent. If that is your case, you may be interested in the in-depth article on pain at the front of the knee.
It absorbs impact. With every step, and even more going downhill or running, the quadriceps works as a brake: it lengthens while it contracts. It is the joint's shock absorber. A quadriceps that does not brake well lets the impact reach cartilage and bone more directly.
It compensates for the ligaments. After an injury to the anterior cruciate ligament, or in an arthritic knee that has lost passive stiffness, muscle strength becomes an important part of the stability available. It is no accident that regaining quadriceps strength is a central goal of any knee rehabilitation.
That said, "protects the knee" does not mean "heals the knee". The difference between the two phrases lies entirely in the numbers, and that is why it is worth looking one by one at the three most common situations.
Knee osteoarthritis: first line, but with modest effects
Let's start with the least debatable point. The 2019 international guidelines of the Osteoarthritis Research Society International list, among the core treatments for knee osteoarthritis, patient education and structured land-based exercise programmes, with or without dietary weight management. Not a supplement, not an injection: exercise.
How large the benefit is, though, is another question. The Cochrane review on exercise in knee osteoarthritis, updated in December 2024, gathered 139 randomised trials and 12,468 participants. Compared with an attention control or a placebo, exercise produces a slight improvement in pain, on average about 8.7 points on a 0-100 scale (a hundred-point scale, not the 0-10 used in the clinic) (confidence interval 5.7 to 11.7), with low certainty of evidence. On physical function the improvement is about 11.3 points out of 100, with moderate certainty.
The comparison with no treatment or usual care is a little more favourable: about 13.1 points out of 100 on pain, again with low certainty, and about 12.5 points on function. The authors point out, however, that most of the studies have an unclear or high risk of bias, and that the participants knew which treatment they were receiving: something that may have contributed to the improvements reported.
In other words: exercise is the right thing to do, it is safe, it does not increase dropouts, but the average gain is modest, not transformative. Anyone who promises that quadriceps strengthening "cures osteoarthritis" is telling a version the data do not support; anyone who says it is useless is just as wrong, because among the options available it remains the one with the best balance of benefit, risk and cost. The full picture of management is in the guide on what to do about knee osteoarthritis.
On the type of strengthening, a network meta-analysis published in PLoS One in 2024 compared isometric, isotonic and isokinetic work in knee osteoarthritis: all three improve pain and function compared with conventional physiotherapy, with the best result for isokinetic, which however requires laboratory equipment and cannot be replicated at home. The useful news for you is the other half: even the "basic" forms, the ones you can do on a mat, have been shown to be effective.
Patellofemoral pain: the quadriceps is not enough
Patellofemoral pain is the pain at the front, around or behind the kneecap, that gets worse on stairs, slopes, squats and after long periods of sitting. For decades it was considered a purely quadriceps problem. Today the view is broader.
The 2015 Cochrane review on exercise therapy for this condition included 31 trials and 1,690 participants, finding consistent but very low quality evidence that exercise may produce a clinically meaningful reduction in pain and improvement in function, as well as supporting long-term recovery. "Very low quality" means the studies were small and methodologically fragile: the direction is clear, the size of the effect is not.
The same review compared exercises for the hip and knee together against knee exercises alone, finding evidence, again of very low quality, that the combination may reduce pain more.
There is also a practical detail worth attention. A randomised trial published in the Journal of Orthopaedic & Sports Physical Therapy in 2011 assigned 33 women with patellofemoral pain to four weeks of hip strengthening or of quadriceps strengthening, before having both groups do the same four weeks of functional weight-bearing exercises. After the first four weeks the group that had started with the hip reported less pain (2.4 versus 4.1 on average). At the end of the eight weeks both groups had improved in a similar way.
The correct reading is this: starting from the hip does not take you further, it takes you there sooner. Relief comes earlier, the end point is the same. It comes from a single small study carried out only on women, so it is a reasonable indication, not a law: but it is a good reason not to build a programme entirely centred on the quadriceps. We discuss the anatomical reason in the article on hip and knee.
After a cruciate ligament reconstruction or surgery
It needs saying straight away: this part is not a do-it-yourself matter. A post-operative programme is built with the surgeon and the physiotherapist following you, because it depends on the type of graft, the associated injuries and the biological healing times. What follows serves to understand the problem, not to replace that programme.
The central problem, after an anterior cruciate ligament reconstruction, is that the quadriceps stays weak for a long time. A meta-analysis published in Knee Surgery, Sports Traumatology, Arthroscopy in 2022 analysed 122 studies covering more than 4,100 operated patients, measuring the difference in strength between the operated leg and the healthy leg. The meta-regression estimates that the difference closes on average at around 54-59 months after surgery: four and a half years, not four months.
The even more concrete figure is another: fewer than 25% of patients reach a quadriceps strength symmetry above 90% between 6 and 12 months after surgery, that is, right in the window in which many return to sport. The authors stress that the great majority return to play with quadriceps strength still significantly impaired, and report larger deficits with patellar tendon grafts than with hamstring tendon grafts. It is a level III study: an estimate, not an individual prediction.
This explains two things. The first is that, after surgery, strengthening is not "the final part of rehabilitation": it is the reason rehabilitation takes so long. The second is that the return to activity is not decided by the calendar, but by strength measurements made by the person following you.
Strengthening the quadriceps without straining the knee
It is the request most people arrive here with: strengthening the quadriceps without straining the knee. It can be done, provided one thing is made clear: "without straining" does not mean "without loading". The muscle only grows if you load it. What can be adjusted is how much the joint works while the muscle works.
The exercises that load the knee least, in order:
- Isometric with the knee straight (contracting the quadriceps while lying down): the muscle works, the joint hardly at all. It is the starting point when even standing still hurts.
- Straight leg raise: the knee does not move, so there is no patellofemoral compression. It is the exercise used in the most irritable phases.
- Isometrics with the knee bent, but at the right angle: in patellofemoral pain the compression grows with flexion, so you start from the angles you tolerate and move up slowly.
- Open chain with a limited range: not the whole arc, only the stretch that does not cause you symptoms the next day.
- Shallow closed chain: half squat or wall squat stopping before the angle that bothers you.
The criterion for knowing whether you are "straining" is not how much you feel during, but whether the next day you are back where you were. If the discomfort builds up from session to session, the dose was too much, not the exercise wrong.
Isometric exercises: where quadriceps strengthening starts
An isometric is a contraction without movement: the muscle works, the joint stays still. It is the starting point when the knee is sore, swollen or recovering from surgery, because it produces muscle tension with the minimum of joint stress.
Quad set. It is the basic exercise, the one almost every programme starts from. Seated or lying with your leg straight, contract the quadriceps as if you wanted to push the knee down, against the bed or the floor. You should see the kneecap move slightly upwards. Hold the contraction for 5-10 seconds, for 3 sets of 15 repetitions.
Wall sit. Back against the wall, feet forward, slide down until your knees are at 45-60° and hold the position. 3 sets of 30-60 seconds. It is a more demanding isometric than the quad set because the muscle works under body weight: introduce it when the quad set no longer costs you effort.
Terminal knee extension (TKE). A band anchored in front of you and passed behind the knee, standing: start with the knee slightly bent and extend it fully against the resistance. 3 sets of 15. It works the final part of the extension, the part that is lost first after an effusion or immobilisation, and it is often the reason people walk with a "springy" gait.
Before you start, make sure of the diagnosis. It often happens that people believe they have one problem when the real cause is another: a meniscus, a tendon, sometimes the hip. Doing the right exercises for the wrong problem for weeks is the most effective way of not getting better.
Open chain exercises: isolating the quadriceps
In open chain the foot is free in space. The advantage is that you load the quadriceps selectively, without asking the rest of the leg to help; the limit is that the movement resembles real life little.
Straight leg raise (SLR). Lying on your back, one leg bent and the other straight: contract the quadriceps first, then raise the straight leg by 30-40 cm, and lower it slowly. 3 sets of 15 per leg. The knee does not move, so the joint load is minimal: it is an exercise that can be done even very soon after surgery, when the person following you authorises it.
Short arc quad. A roll or rolled-up towel under the knee, and extend the leg from about 30° to 0°. 3 sets of 15. It serves to work in a protected range of movement when full flexion is still painful.
Leg extension. Seated, extend the leg against a resistance (machine or ankle weight). 3 sets of 12-15, with moderate loads. It is the most "muscular" of the three, but also the one that loads the patellofemoral joint most in the initial part of the movement: if your pain is at the front, it should be introduced with caution and never in jerks.
A clarification, because a fair amount of misinformation circulates: after anterior cruciate ligament reconstruction, open chain was long avoided for fear that it would stress the graft. A meta-analysis published in the Journal of Orthopaedic & Sports Physical Therapy in 2018 compared the two families in this population, across ten studies, and found no differences in anterior tibial laxity, strength or patient-reported function, at any point of the follow-up and with both early and late introduction of open chain. The quality of the evidence ranges from limited to moderate.
The historical fear is therefore scaled back, but with a clarification that matters: "there are no differences" does not mean "do what you like whenever you like". After surgery the timing is decided by your surgeon and your physiotherapist, who know the graft and the associated injuries. An article can take away an unfounded fear, not give you the green light.
Closed chain exercises: training the movement
In closed chain the foot is fixed on the ground and the whole leg works together. These are the exercises most similar to what you actually do, that is, getting up, climbing, walking, and they are generally introduced when the pain is under control.
Mini squat. Feet shoulder-width apart, weight towards the heels, bend your knees to about 45° and come back up. 3 sets of 15. Your knees follow the direction of your toes: if they fall inwards, reduce the depth or slow down.
Step up. Step up onto a step controlling the climb and above all coming down slowly. 3 sets of 10 per leg. The descent is the part that trains eccentric strength, that is, precisely the braking ability we were talking about. Start with a low step.
Lunges. One step forward, bend both knees, return. 3 sets of 10 per leg. It requires strength and balance together, and it is the most advanced of the group: it only makes sense when mini squats and step ups are by now easy.
Leg press. Push against the resistance without ever locking your knees in full extension. 3 sets of 12. It allows you to load quite a lot with your back supported: useful when you really need to progress the load.
Open chain or closed chain: how to choose
The practical differences, in brief:
- Position of the foot. Free in space in open chain, resting on the ground in closed chain.
- What you train. The quadriceps in isolation with open chain; the whole leg as it works in daily life with closed chain.
- Joint load. More targeted and controllable in open chain; more spread out but overall higher in closed chain.
- Examples. Open chain: straight leg raise, short arc quad, leg extension. Closed chain: mini squat, step up, lunges, leg press.
- When you need them. Open chain when a specific muscle lacks strength; closed chain when the goal is to get back to stairs, walking and sport.
In patellofemoral pain the 2015 Cochrane review examined four studies comparing the two families without being able to establish which was superior. In practical terms: there is no "right" family of exercises, there is the one your knee tolerates today. And that is why this guide insists on the order more than the list.
The three-phase progression of quadriceps strengthening
- Phase 1, foundation. Isometrics and open chain: quad set, straight leg raise, wall sit. Indicative duration 2-3 weeks.
- Phase 2, light closed chain. Mini squat, low step ups. Indicative duration 3-4 weeks.
- Phase 3, load. Exercises with external load, lunges, high step ups. Progressive duration, no deadline.
The durations are indicative, not a calendar. The criterion for moving up a phase is not time: it is that the exercises of the current phase have become easy and leave no pain or swelling the next day. If in the morning the knee is hotter or stiffer than before, you have taken too long a step: go back a level and try again in a few days.
Dosage: what comes from studies and what from practice
The numbers of sets and repetitions are often presented as if they had been validated one by one. They have not.
What comes from the studies is the principle: a progressive load, increased in steps, within a structured and ideally supervised programme. The OARSI guidelines speak precisely of structured programmes, not of scattered exercises; the Cochrane review on osteoarthritis pools interventions of 2 to 104 weeks and does not allow an optimal scheme to be indicated.
What comes instead from clinical practice, and should be declared as such, are the numbers: the 3 sets of 15, the 5-10 seconds of contraction, the 3 workouts a week. They are widely used reference points and generally well tolerated, not doses shown by a study to be superior to others. If your physiotherapist gives you different ones, there is probably a reason that concerns you.
On frequency, three workouts a week remain the reasonable compromise between stimulus and recovery. In the very early phases, with only very low load isometrics, you can work every day; as the load rises, rest days are really needed.
Warning signs: when to stop and get assessed
In some situations the problem is not the dosage of the exercise. Stop and get assessed without waiting if any of these pictures appears:
- Hot, swollen and red knee with fever or general malaise. An inflamed joint together with systemic signs needs to be seen straight away, not trained.
- Joint locking. The knee stops in one position and will not extend or bend fully, or it "catches" and a manoeuvre is needed to free it.
- True giving way. Not insecurity or the feeling of a weak leg, but the knee that really goes and makes you lose your footing or fall.
- Significant swelling in the hours after an injury. A rapid effusion, within a few hours of a sprain or a knock, deserves assessment before starting any programme.
- Night pain at rest. A pain that wakes you and does not depend on movement is not an overload pain and needs to be investigated.
- Progressive worsening despite weeks of well-conducted work. If the picture does not move or goes backwards, the diagnosis needs to be reviewed.
None of these signs automatically means something serious: they mean you need a professional to look before you continue.
How to strengthen the quadriceps without straining the knee
It is the question almost everyone asks, and the answer is that you change where the load sits, not how hard the muscle works.
The knee suffers above all when the joint bends under load and when the foot is free to move in the air. So:
- Work at angles where you feel fine. The quadriceps strengthens with the knee almost straight as much as with the knee bent: if 90 degrees bothers you, you work between 0 and 30 and still gain strength.
- Use isometrics. Pushing against something that does not move (your straight leg pressing on a towel rolled up under the knee, ten seconds) loads the muscle while leaving the joint still. It is the first building block when the knee is irritable.
- Keep the foot on the ground. Closed chain exercises (foot on the floor) spread the load across hip, knee and ankle together, instead of concentrating it on the kneecap.
- Look at the 24 hours after, not the moment. If the next day the knee is hotter or more swollen, you asked too much: you go back a level, you do not stop.
None of these measures slows down the strengthening: they change the road, not the destination.
Mistakes to avoid
Reducing everything to quadriceps strengthening. It is the most widespread mistake. A systematic review published in the British Journal of Sports Medicine in 2020 assessed what happens when hip exercises are added to work on the quadriceps in knee osteoarthritis: across eight studies, the combination was found to be better for walking function, while on the pooled data for pain, self-reported function and scales no significant difference emerged. In the subgroup analyses, however, resistance exercises for the hip proved more effective than neuromuscular functional ones. It is not overwhelming proof, but it points in the same direction as the Cochrane review on patellofemoral pain.
Forcing through pain. Mild discomfort during the exercise is acceptable and often unavoidable. Intense pain, or discomfort that increases set after set, is not: it is a signal, not proof of commitment. The most reliable parameter remains how the knee is in the following 24 hours.
Skipping isometrics because they "seem like little". They are the only way of producing tension when the joint does not tolerate movement, and in the 2024 network meta-analysis isometric work also improves pain and function.
Training only the climb. Coming down the stairs, braking when running and landing from a jump are eccentric work, and it is what the quadriceps loses first.
Stopping when the pain goes. Pain goes before strength does, and after surgery the deficit can persist for years. Stopping at the first relief is the most common way of finding yourself back at the starting point.
What we really know, and what we do not
We know that exercise is recommended as a core treatment in knee osteoarthritis, that it is safe and that those who do it in the studies do not drop out more than the control groups. We know that in patellofemoral pain it reduces pain and improves function consistently across studies. And we know that after a cruciate ligament reconstruction the quadriceps strength deficit is the rule, not the exception, and lasts much longer than people imagine.
We do not know the optimal form of exercise: the authors of the Cochrane review on patellofemoral pain say so explicitly. And we cannot establish precisely the size of the benefit, because the certainty of the evidence on pain is low in both conditions. Anyone who promises you the definitive protocol is going beyond the data.
What remains true, and useful, is the method: start from a load the knee tolerates, increase it gradually, include the hip, train the braking as well, and judge by the next day's symptoms.
Conclusion
Quadriceps strengthening is not an exercise, it is a progression. First you build tension without movement, then movement without load, finally real load. Skipping steps is the quickest way to inflame a knee that was getting better.
If your knee has been sore for a while, gives way, swells after activity or does not recover after surgery, the choice of exercises and of the moment to introduce them needs to be tailored to you. A broader picture is on the page dedicated to the knee.
Wondering how much it would cost to be followed? The cost depends on how many sessions are needed, not on the single rate: you will find the sums in How much physiotherapy for the knee costs.
Do you need a consultation?
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If the quadriceps struggles to switch on after surgery, see Muscle electrical stimulation: is it really worth it?.
Sources
- OARSI guidelines for the non-surgical management of knee, hip, and polyarticular osteoarthritis, Osteoarthritis and Cartilage, 2019
- Exercise for osteoarthritis of the knee, Cochrane Database of Systematic Reviews, 2024
- Effects of three types of resistance training on knee osteoarthritis: A systematic review and network meta-analysis, PLoS One, 2024
- Exercise for treating patellofemoral pain syndrome, Cochrane Database of Systematic Reviews, 2015
- Hip strengthening prior to functional exercises reduces pain sooner than quadriceps strengthening in females with patellofemoral pain syndrome, Journal of Orthopaedic & Sports Physical Therapy, 2011
- Does adding hip exercises to quadriceps exercises result in superior outcomes in pain, function and quality of life for people with knee osteoarthritis?, British Journal of Sports Medicine, 2020
- The Effect of Open- Versus Closed-Kinetic-Chain Exercises on Anterior Tibial Laxity, Strength, and Function Following Anterior Cruciate Ligament Reconstruction, Journal of Orthopaedic & Sports Physical Therapy, 2018
- Time, graft, sex, geographic location, and isokinetic speed influence the degree of quadriceps weakness after anterior cruciate ligament reconstruction, Knee Surgery, Sports Traumatology, Arthroscopy, 2022
Last source check: August 2026.
