The knees experience pressure equal to approximately 3 times the body's weight when walking and approximately 5 times the body's weight when running. In other words, a person who weighs 150lbs puts about 750lbs of pressure on the knee when landing each running stride.
Not surprisingly, the knee is the most frequently injured joint in runners and non-runners alike.
Runner's knee: patellofemoral pain syndrome
When people say they have "runner's knee," they are typically referring to patellofemoral pain syndrome. "Patella" means kneecap and "femur" means thighbone, so patellofemoral pain is pain that originates between the kneecap and thighbone. The pain is felt at the front of the knee, either under or around the edges of the kneecap.
Read more: What You Need to Know About Runner’s Knee
The root of patellofemoral pain can vary and may be difficult to identify. For example, the kneecap may not glide well along the groove in the femur (thighbone), or relatively weak hip muscles may cause a runner to over-rely on quadriceps muscles, which then tug uncomfortably on the kneecap.
Patellofemoral pain is typically more noticeable going up stairs or walking or jogging uphill.
Iliotibial (IT) band syndrome
Iliotibial band syndrome can affect both novice and experienced runners. The pain tends to be sharp and isolated to the area just above or at the knobby outside of the knee. IT band syndrome does not cause redness, swelling, or knee instability.
The iliotibial band, or IT band, is a thick piece of fibrous tissue that begins at the hip, extends along the outside of the thigh, and attaches to the top of the tibia, or shinbone. When the knee bends, the IT band must glide over the outside of the knee joint, including the bulbous end of the femur called the lateral condyle. If the IT band becomes tight from strain or overuse, it can rub against the lateral condyle and become inflamed, causing pain.
Read more: Iliotibial Band Syndrome
Unlike patellofemoral pain syndrome, the IT band pain is often worse when going down stairs or jogging downhill.
Commonly called "jumper's knee," patellar tendinitis can cause pain at the front of the knee, at the lower kneecap or the bony bump at the top of the shin. The pain may be minor and felt only when exercising, or it may be severe enough to affect a person's daily activities, such as going up stairs. Along with pain, a person may notice swelling, redness and warmth.
Read more: Understanding Jumper’s Knee
A tendon connects muscle to bone and a ligament connects bone to bone. The patella tendon is actually a ligament that connects the patella (kneecap) to the upper tibia (shin bone). When the patellar tendon becomes inflamed and causes painful symptoms it is called patellar tendinitis. It tends to be an overuse injury that is common in runners, particularly people who run on downhill inclines, and people who participate in sports that require a lot of starting and stopping.
Achy, stiff, and possibly swollen knees may be signs of osteoarthritis. Experts debate whether or not regular running for exercise causes knee osteoarthritis.
Some experts argue that running does not cause knee osteoarthritis, but that people who already have knee osteoarthritis may accelerate the wear-and-tear on their knee joint by running regularly. Many health advocates assert that running regularly for exercise provides other health benefits, such as weight control, that outweigh potential arthritic damage to the knees.
Knee arthritis may cause a runner to feel achy in the knees during or after a workout. In addition, knees may feel stiff and painful when squatting, climbing stairs, and after prolonged inactivity, such as when getting out of bed in the morning.
For more in-depth information, see Knee Osteoarthritis on Arthritis-health.com.
The meniscus is a C-shaped pad of cartilage that separates the tibia and the femur and provides cushion and stability. It can be damaged in a single traumatic injury or degrade over time through mini-traumas. People who are older, who run on uneven surfaces, or who make sudden turns and hard stops (e.g. soccer players) are at the greatest risk for damage to the meniscus.
A person with a torn meniscus can experience knee pain, swelling and stiffness. In addition, the knee may give way or lock if a piece of the torn meniscus prevents joint movement. Surgical repair is sometimes, but not always, recommended.
Running with a knee injury can exacerbate the pain and further the injury. If a person rests the painful knee for a couple of weeks and still experiences pain, or if pain is severe, medical attention is warranted. An orthopedist or primary care physician can make a diagnosis and recommend treatment.