If you’ve ever developed knee pain after exerting yourself during walking or another workout, then you probably quickly gained an appreciation for what a healthy knee can do: fully straighten and bend without pain. The knee’s ability to bend often gets all the glory as the primary movement we associate with sitting, squatting, and climbing stairs. But the knee’s ability to straighten is also an unsung hero in walking, standing, balancing, and more. Many issues can interfere with your ability to straighten your knee, including inflammation and swelling, overexertion, weak quads (thigh muscles), arthritis, or a sports injury. While this can be challenging, there are ways to manage it and improve your knee’s range of motion. 

Knee extension exercises help counteract difficulty straightening the knee. “The two key benefits of knee extensions are that they help you regain full range of motion in the knee, and they strengthen the quads (or thigh muscles), which are the primary muscles that straighten the knee,” says Mary Kimbrough, PT, DPT, OCS, a physical therapist at Hinge Health. Strengthening the quads also takes some load off your knees, helping to ease knee pain from a variety of contributing factors. 

Read on to learn why knee extensions are so good for lifelong knee health, plus get knee extension exercises suggested by our physical therapists with tips to maximize their benefits. 

Why Is Knee Extension Important? 

Having full knee extension — the ability to completely straighten your knee — allows you to do a huge range of activities, including: 

• Reducing long-term knee pain. Because knee extensions improve basic knee mechanics, they can help keep knees healthy and strong as you age, says Cody Anderson, PT, DPT, a physical therapist at Hinge Health.

• Balance. Your ability to balance depends on your ability to fully extend your knees. Lack of extension can contribute to falls during regular activities like walking on uneven ground, or cause you to trip over objects like rugs and electrical cables at home. 

• Standing and walking. Full knee extension allows you to walk and stand efficiently and without pain. To walk with a normal gait, you need to be able to straighten the leg you’re standing on as you swing the other one forward, says Dr. Kimbrough. “If something prevents full extension, the load doesn’t go where it normally goes and it has to get distributed somewhere else.” This may put extra pressure on the kneecap or quad muscles which can cause pain or discomfort in those areas if your body isn’t used to it. It’s also possible that your hips and back will compensate for the change in your gait related to lack of knee extension. In some cases, this can lead to hip and lower back pain, says Dr. Anderson.

What Causes Issues with Knee Extension?

Just about any type of knee pain — no matter what’s behind it — can hinder knee extension, says Dr. Anderson. Here are some common examples:

Swelling. “Swelling creates extra volume in the spaces within the joint, making it harder to bend and straighten,” says Dr. Kimbrough. Swelling commonly occurs after an injury or surgery as a part of the body’s healing process. See remedies to reduce swelling below.

Surgery or a period of knee immobilization. If you’re not able to move your knee for a short period of time, it’s common for the knee to lose range of motion and feel stiff, says Dr. Kimbrough. ACL and meniscus tears or a total knee replacement often restrict the range of motion at first. “Different bodies heal at different paces,” says Dr. Kimbrough. “Some people get their range of motion back really quickly, and for others, it just takes a little longer.”

Patellar tendinitis. “This is one of the top conditions that I have people do knee extensions for,” says Dr. Anderson. Patellar tendinitis (also called jumper’s knee) is an overuse injury that affects the ligament connecting the kneecap and shin bone. In some cases, it contributes to pain and tenderness just below the kneecap. Knee extension exercises put force through the patellar tendon, strengthening its ability to bear the stress, says Dr. Anderson. One study found that a routine of leg extension exercises helps reduce the pain of patellar tendinitis in 12 weeks. 

Patellofemoral syndrome. Also known as runner’s knee, the patellofemoral syndrome is an overuse injury that affects the patellofemoral joint in the knee, causing a dull ache behind the knee cap. “It can also affect people who regularly have to sit for long periods of time without breaks because sitting puts the joint in a more compressed position,” says Dr. Anderson. Lots of sitting also prevent many people from using the knee’s full range of motion throughout the day. Leg extensions help by getting the joint moving and by strengthening the joint and surrounding structures.

 Meniscus tear. Just like all structures in the body, the menisci — the discs that cushion the knee joint — change with age. A meniscus injury can, in some cases, lead to pain, stiffness, swelling, reduced range of motion, or catching or locking sensation when straightening the knee. Knee extension exercises help certain kinds of meniscus tears, says Dr. Anderson, because they help the joint build tolerance to the “slide and glide” motions during knee movement.   

Weak quads. The quadriceps muscles in the thigh are responsible for extending the leg and supporting overall knee function. So if the quads don’t have enough strength, it can cause knee pain and dysfunction, says Dr. Kimbrough. One of the major benefits of knee extension exercises is stronger quadriceps. “If you have knee pain and you also have weak quads, strengthening those quads is a good starting point in addressing your pain,” says Dr. Anderson. “Your joint will feel better because now it has the strength to move.” 

Tight hamstrings. The hamstrings (muscles along the back of your thigh) contract to help bend the knee. If they’re tight, the hamstrings can actually limit knee extension, says Dr. Kimbrough. Stretching hamstrings to lengthen them can help you move further into knee extension.

Arthritis. With osteoarthritis, the cartilage that cushions the knee joint wears over time. This may lead to aching and stiffness and can make everyday movements more difficult for some people. Arthritis looks different for everyone, but it can, in some cases, affect knee range of motion, even if it doesn’t require surgery, says Dr. Kimbrough.“I often recommend stretching hamstrings as a way to move into knee extension when arthritis is a factor in stiffness.”  

What Improves Knee Extension? How Long Does It Take?

The knee is a hinge joint that mainly moves back and forth, with a bit of side-to-side rotation. The quadriceps (front thigh muscles) contract to extend or straighten the knee. The hamstrings (back thigh muscles) contract to bend the knee. Therefore, rehabilitation exercises to improve knee extension often focus on two main components:

• Strengthening the quads

• Stretching and lengthening the hamstrings

Most people see reduced pain and a greater ability to be active after about six weeks of rehabilitative exercises, says Dr. Kimbrough, though there are some situations where it can take a shorter or longer period of time, such as after a total knee replacement surgery. 

No matter what factors contribute to challenges in straightening your knee, exercise helps. Here are a few gentle exercises from Hinge Health that you can try. 

The information contained in these videos is intended to be used for educational purposes only and does not constitute medical advice or treatment for any specific condition. Hinge Health is not your healthcare provider and is not responsible for any injury sustained or exacerbated by your use of or participation in these exercises. Please consult with your healthcare provider with any questions you may have about your medical condition or treatment.

4 Tips for Knee Extension Exercises: Maximize the Benefits

To make the most of your knee extension exercises, consider these tips from Hinge Health physical therapists:   

1. Return all the way to the starting position. “It’s important to move muscles through their whole range of motion,” says Dr. Kimbrough. “Range of motion is a ‘use it or lose it’ kind of thing.” This holds true for the bending portion of knee extension exercises, as well as the straightening portion. 

2. Go slow. Stay steady. You want your movements to be smooth and controlled. “That often means telling people to slow down,” says Dr. Kimbrough, instead of kicking up and down quickly. This, along with returning to the starting point, makes the muscle work over a longer time and range, which helps strengthen and improve mobility.

3. Keep your leg straight. Whether on a gym machine or using a band at home, when you kick your leg out, concentrate on keeping it straight. If you turn your leg to the side, you start involving the hip flexors in the movement. You want to feel the full force of the move on the quadricep muscles in the thigh, says Dr. Anderson.  

4. Start with a light weight and build up. Dr. Anderson recommends a smart progression of building strength. You should be able to do 12 to 15 repetitions at your chosen weight without irritating the joint or aggravating any injury. Ideally, you would be able to do two or three sets. Once knee extensions become easier to do, you can keep strengthening the quadriceps by adding resistance, says Dr. Kimbrough. Try adding ankle weights or resistance bands to your knee extension exercise, or adding more weight if you use a knee extension machine at the gym.

Other Treatment Options for Knee Pain

If you have swelling due to surgery, an injury, osteoarthritis, or another issue, controlling that swelling may help you regain your range of motion more quickly. These steps can reduce pain and swelling:

• Apply ice. Apply ice or a cold pack for 10 to 20 minutes at a time over the course of an hour or two. Place the ice pack over a damp towel, and check your skin occasionally. (Pink or red skin is normal; rashes are not.)

• Adjust your usual exercise routine. It’s okay to take it easy while pain is acute, but continue to walk and be active to the extent that you can, says Dr. Kimbrough. Nudging into pain or discomfort during activities you enjoy helps improve your range of motion and resilience to pain. 

• Keep moving your leg. “Curl your toes. Pump your ankle up and down. Anything that keeps the blood moving through your legs helps reduce swelling and the chance of blood clots,” says Dr. Kimbrough. You can also do heel slides in bed (see exercises above).

• Raise it up. When you do rest, lay your leg on pillows so it is elevated above your heart.

• Use compression. Consider wrapping your knee with a compression stocking to further reduce swelling.  

PT Tip: Let Gravity Do the Work

If you are having trouble fully extending your knee, lie on your stomach on your bed with your knees and shins hanging off the edge, recommends Dr. Kimbrough. (The edge of your bed should hit just above the knee.) Then, let gravity stretch your knee into extension. You should feel a stretch in the back of your thigh and knee. Start by holding the stretch for 30 seconds, but feel free to hold it for as much as a few minutes if that feels good to you. If you’re recovering from an acute injury, for example, 30 seconds may feel best. If you’re dealing with ongoing stiffness in the knee, you might feel comfortable going a bit longer. 

How Hinge Health Can Help You

If you have joint or muscle pain that makes it hard to move, you can get the relief you’ve been looking for with Hinge Health’s online exercise therapy program.

The best part: You don’t have to leave your home because our program is digital. That means you can easily get the care you need through our app, when and where it works for you.

Through our program, you’ll have access to therapeutic exercises and stretches for your condition. Additionally, you’ll have a personal care team to guide, support, and tailor our program to you.

See if you qualify for Hinge Health and confirm free coverage through your employer or benefit plan here.

This article and its contents are provided for educational and informational purposes only and do not constitute medical advice or professional services specific to you or your medical condition.

References

1. Bump, J. M., & Lewis, L. (2022). Patellofemoral Syndrome. In StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih.gov/books/NBK557657/

2. Cameron, M.  2013. Physical Agents in Rehabilitation (6th edition). Elsevier Health Sciences U.S. https://bookshelf.vitalsource.com/reader/books/9780323829304

3. Cannell, L. J., Taunton, J. E., Clement, D. B., Smith, C., & Khan, K. M. (2001). A randomised clinical trial of the efficacy of drop squats or leg extension/leg curl exercises to treat clinically diagnosed jumper’s knee in athletes: Pilot study. British Journal of Sports Medicine, 35(1), 60–64. doi:10.1136/bjsm.35.1.60

4. Deshpande, B. R., Katz, J. N., Solomon, D. H., Yelin, E. H., Hunter, D. J., Messier, S. P., Suter, L. G., & Losina, E. (2016). The number of persons with symptomatic knee osteoarthritis in the United States: Impact of race/ethnicity, age, sex, and obesity. Arthritis Care & Research, 68(12), 1743–1750. doi:10.1002/acr.22897

5. Sheth, N. P. (2022, April). Osteoarthritis. OrthoInfo — American Academy of Orthopaedic Surgeons. https://www.orthoinfo.org/en/diseases--conditions/osteoarthritis/

6. Wittstein, J. R. & Wilkerson, R. (2021, September). Patellar Tendon Tear. OrthoInfo — American Academy of Orthopaedic Surgeons.. https://www.orthoinfo.org/en/diseases--conditions/patellar-tendon-tear/

7. Raj, M. A., & Bubnis, M. A. (2022). Knee Meniscal Tears. In StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih.gov/books/NBK431067/