eli5: how does it work that for every pound of weight you lose, there is a 4 pound stress reduction in your knees?

Question

eli5: how does it work that for every pound of weight you lose, there is a 4 pound stress reduction in your knees?

In: 1542

Answer 1

Your body weight in pounds is the so-called ‘static load’; I.E. your weight while still and unmoving. When you walk, each heel-strike has considerably more force than your weight in pounds: your body is under the strain of the ‘dynamic load’ of your mass moving under the effect of gravity.

As a simple analogy, compare a rock sitting on a surface to picking that same rock up to your center of gravity and dropping it. Obviously the dropped rock has a much greater force, as its kinetic energy multiplies the weight. In the same fashion, walking and running multiplies the forces acting on your joints.