Our knees hold us up and allow us to propel forward, yet we often give them very little thought until they start to tell us that the strain is taking its toll. When we consider that they can bear 5-12 times our weight when we break into a run, we can see how their function is crucial for supporting ourselves against the force of gravity. They are the largest joints in the body because they need to be.
Our knees are essentially hinge joints, with a back-and-forth motion from extending the lower leg to straight and flexing it back, in our natural walking motion. They also have some capacity to rotate inward and outward, which gives them flexibility but can also make them prone to injury. With the modern trend to sit on chairs rather than on the floor as our skeleton evolved to do, we often have reduced range of motion in the hips—which are ball-and-socket joints with a wider natural range of motion—and the knees experience more rotation than their design allows. This 'torquing' across the knees can create pull that we feel as stiffness or pain, as well as cause tissue inflammation that has been shown to contribute to rheumatoid and osteoarthritis.
As our knees bear 1.5 times our weight when we walk, we can also overburden them if we put on excess weight. Population studies have consistently shown links between obesity and osteoarthritis. Obese women have nearly four times the risk of knee osteoarthritis compared with non-obese women, and for obese men, the risk is nearly five times greater.1 But the connection between obesity and osteoarthritis is not simply about weight on the joint—the adipose (fat) tissue that accumulates in overweight and obesity also promotes inflammation, a known trigger for all types of arthritis.2
For many, knee issues can mean less ability to move and greater likelihood of putting on weight, so attending to our knees in ways that enable our basic daily walking needs—initially without weight-bearing—is crucial for our overall health.