Top Reasons for Knee Stiffness After Sitting Too Long

Stiffness, swelling, and pain are common symptoms of arthritis and worsen with inactivity. Patellofemoral pain (PFP) causes kneecap discomfort that’s aggravated when the knee is flexed for too long. If your knee stiffness is frequent and unexplained, a discussion with your doctor is likely necessary. However, the following issues may result from awkward sitting positions or improper chair and desk height.

The knee contains bones, cartilage, ligaments, tendons, and muscles. These pieces move and flex as needed to bend your knee when sitting. Prolonged seated positions strain the knee and surrounding area, causing tightness and discomfort.

Altered synovial fluid levels in the joint also cause knee stiffness after sitting. Synovial fluid lubricates the joints during movement. Seated positions restrict fluid movement, which can prevent proper circulation and lead to joint tightness. After standing, slow movements or gentle exercises encourage lubrication to reduce stiffness.

According to experts, approximately 1 in 4 people experience tight muscles as a chronic condition. It is often related to exercise or other vigorous activities. It may also be a symptom of Meningitis, tetanus, fibromyalgia, or another serious infection or disease.

However, stiffness in the knee after sitting is likely due to muscle imbalances. The muscles supporting the knee joint weaken while seated. Other muscles, including the hip flexors, tighten in prone positions. The longer you sit, the higher the muscle imbalance, and the more altered your knee alignment becomes.

Your knees are under more strain and wear than any other joint in the body. It also contains several small sacs, called bursae, filled with synovial fluid. Sometimes, these release more fluid than they’re supposed to, causing effusion, which is a buildup of fluid in the knee.

Such buildup inflames the area, causing swelling, pain, and reduced flexibility. Effusion usually results from injuries, inflammatory conditions, or overactivity. However, it may also occur after sitting too long, causing knee stiffness until the fluid disperses.

Poor circulation is another possible cause of knee stiffness after sitting. Your heart rate is normally faster when you’re standing and moving than when seated. The area pressed against the chair also compresses the veins, further slowing circulation.

Your knee also flexes when you sit down, restricting blood flow through the leg to the foot and back. These factors all prevent the blood from flowing at its normal rate. This could cause the knee to stiffen until you stand and allow proper circulation to resume.

Resources:

1. CDC, March 13, 2025Arthritis
   https://archive.cdc.gov/#/details?url=https://www.cdc.gov/chronicdisease/resources/publications/factsheets/arthritis.htm
2. JOSPT, July 31, 2016, Pain During Prolonged Sitting is a Common Problem in Persons With Patellofemoral Pain
   https://www.jospt.org/doi/full/10.2519/jospt.2016.6470?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed
3. Integris Health, July 14, 2025, Why Does Sitting for Long Periods of Time Hurt My Knees?
   https://integrishealth.org/resources/on-your-health/2025/july/why-does-sitting-for-long-periods-of-time-hurt-my-knees
4. Cleveland Clinic, Muscle Stiffness
   https://my.clevelandclinic.org/health/symptoms/25147-muscle-stiffness
5. Trilogy, How Prolonged Sitting Can Cause Knee Pain
   https://mytrilogy.org/how-prolonged-sitting-can-cause-knee-pain/#:~:text=Muscle%20Imbalances%3A,risk%20of%20pain%20and%20injury
6. NCBI, Feb. 26, 2024, Knee Effusion
   https://www.ncbi.nlm.nih.gov/books/NBK532279/
7. Singapore Heart Foundation, Oct. 30, 2023 In the Air and in Your Veins
   https://www.myheart.org.sg/heart-news/in-the-air-and-in-your-veins/#:~:text=Conclusion%20Although%20Deep%20Vein%20Thrombosis%20is%20usually,blood%20flow%20behind%20the%20knees%20by%2050%25