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

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

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Knees, ankles and hips take a shock load when walking. I did some training where they had a force pad at the bottom of some stairs. You could do 3 to 4 times your actual body weight on that last step if you are rushing down the stairs.

Force not weight. If you weigh a pound of fat, it shows 1lb. If you throw that same piece of fat it will generate more than a pound of force. Knees take forces.

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.

Earths gravity pulls us constantly *and exponentially.* the longer you fall towards the earth from above, the more you accelerate and thus, the more force your impact carries when you land.