Why Does Sitting for Long Periods of Time Hurt My Knees?

When it comes to sitting-related pain, most people picture a stiff neck or an aching back, but knee pain is also a surprisingly common issue that often goes overlooked.

The knee is a complex joint, relying on a delicate balance of muscles, ligaments and cartilage to function smoothly. Sitting for extended periods can disrupt that harmony, leading to discomfort or stiffness. This blog will uncover the intricate structure of the knee and explore why prolonged sitting can trigger pain.

We speak to Katy Lane, a physician assistant with INTEGRIS Health Orthopedics Central, to learn more. 

“We see many patients in our practice with knee pain who tend to lessen their activity leading to stiffness and a further increase in pain,” Lane says. “While the first few steps can be uncomfortable, patients often find that once they get moving, the knees start feeling better.” 

What happens to the knees when you sit?

Key points: When you sit, the position of your knee joint changes significantly compared to when you’re standing or walking. Sitting places the knees in a flexed position, typically at a 90-degree angle or more, depending on your posture and chair height. This position involves several key muscles, tendons, ligaments and joints working together to maintain stability and alignment, and it can also put strain on these structures depending on how you sit and for how long.

The knee is a hinge joint made up of three main bones – femur, tibia and patella.

• When you sit, the tibia and femur stay connected at the knee joint, but the angle sharply decreases, bringing the tibia closer to the femur.
• This compressed angle can sometimes put extra pressure on the cartilage that cushions these bones, particularly on the underside of the kneecap.

Cartilage plays a critical role in cushioning the knee joint and absorbing loads.

• When the knee is flexed during sitting, areas of the menisci and articular cartilage experience sustained pressure.
• Prolonged sitting without movement can reduce the flow of synovial fluid, which lubricates the joint, causing stiffness and discomfort.

Ligaments (ACL, PCL, MCL and LCL) stabilize the joint.

• While sitting, these ligaments are not under significant tension since the knee isn’t bearing weight.
• However, awkward or prolonged sitting positions, such as crossing your legs, may place uneven strain on them over time.

Tendons, such as the patellar tendon, connect muscles to the knee and facilitate movement. 

• During sitting, tendons generally relax, but prolonged inactivity can cause tightness or stiffness, especially in adjacent muscles like the hamstrings or quadriceps.

Muscles around the knee can also become tight during prolonged sitting.

• The quadriceps at the front of the thigh and the hamstrings at the back of the thigh are key muscle groups involved in knee movement and stability.
• While sitting, these muscles are in a relaxed or shortened state.
• The calf muscles and those of the hip flexors also contribute to knee alignment.
• Prolonged sitting can lead to tightness in these areas, indirectly affecting the knee’s range of motion and overall stability.

Causes of knee pain after sitting

What to know: Knee pain after sitting for extended periods is a common issue and can affect people of all ages. For many, it feels like a dull ache or stiffness that becomes more pronounced as they attempt to stand or move. This type of discomfort can have several possible causes, ranging from muscle imbalances to underlying medical conditions.

Patellofemoral pain syndrome (PFPS), often referred to as "runner’s knee," is a common cause of knee pain during or after prolonged sitting. 

• This condition occurs when the cartilage under the kneecap becomes irritated due to improper alignment of the kneecap (patella) within its groove.
• Extended sitting, particularly when the knees are bent, increases pressure on the knee joint and surrounding tissues, which can lead to pain.

Arthritis (osteoarthritis and rheumatoid arthritis) can break down cartilage in the joint, leaving bones to rub against one another. 

• Sitting for a long time restricts joint movement, causing stiffness and discomfort in people with arthritis.
• This is especially common in older adults or those with a history of joint injuries.

Iliotibial (IT) band syndrome is tightness or inflammation of the connective tissue that runs along the outer thigh.

• This tightness can cause referred pain to the outer knee, particularly after sitting in a compressed or awkward position for prolonged periods.

Poor posture, whether it's slouching or sitting with your knees bent at extreme angles, puts extra strain on the knees and surrounding muscles. 

• Over time, poor sitting posture can lead to tight quads and hip flexors, destabilizing the knee joint and causing pain.

Circulation problems can occur when blood flow is reduced to the lower extremities. 

• This can lead to stiffness or numbness in the knees and legs, as well as discomfort when movement is resumed.
• Chronic poor circulation may make these symptoms worse.

Additional risks include lifestyle and age factors.

• Prolonged sitting without breaks, typical in desk jobs, can increase discomfort.
• Aging increases the risk of degenerative joint issues like arthritis.
• Both overly intensive activities and a lack of regular exercise can stress the knees in different ways.
• Prior knee injuries or chronic inflammation can make certain individuals more prone to pain after sitting.

How to improve or prevent knee pain when sitting

Final takeaways: To improve or prevent knee pain when sitting, start by maintaining good posture with your feet flat on the floor and your knees at a 90-degree angle. Avoid staying in one position too long and take breaks every 30 to 60 minutes to stretch or walk around, which helps restore blood flow and reduce stiffness. Using a supportive chair or cushions can also alleviate pressure on the knees, ensuring long-term comfort.

Regular movement is key when taking stress off the knees.

• Avoid sitting for too long in one position.
• Stand up, stretch or take a short walk every 30 to 60 minutes to keep your joints and muscles active.

Focus on posture correction so your knees feel supported.

• Sit with your back straight, shoulders relaxed and knees at a 90-degree angle.
• Ensure your feet rest flat on the ground.

Strengthen and stretch the areas around your knees.

• Incorporate exercises to strengthen your quads, hamstrings and glutes.
• Stretches targeting the IT band and hip flexors can help alleviate tension and reduce discomfort.

Use supportive aids in your chair.

• Ergonomic chairs that provide lumbar and knee support can help.
• Adding a small footrest can also relieve some pressure on the knees.

Apply ice or heat to your knee after sitting.

• An ice pack can reduce swelling, while heat therapy soothes stiffness in the joint.

Get new footwear to support your feet.

• Flat or worn-out shoes may contribute to knee misalignment.
• Opt for footwear with good arch support to reduce strain.

Next steps: If pain persists or worsens, especially when accompanied by swelling or mobility limitations, it’s essential to see your primary care physician and consult with an INTEGRIS Health Orthopedics specialist. Conditions such as undiagnosed arthritis, ligament injuries or chronic PFPS have better outcomes when addressed early. 

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