While walking, the maximum force on your legs exceeds the weight they normally support by quite a bit, although the exact factor depends on how you walk.
If when you walk, you donít bounce up and down (this is not how people usually walk, but it is easier to think about), and each foot is in contact with the ground 50% of the time, the maximum weight on the legs will be about twice what they usually support, because only one leg is holding you up at a time and the weight is not shared. When a foot is lifted off of the ground, it supports no weight.
If you bounce up and down a bit when you walk, the legs must supply the force needed to do that. This force depends on if the bouncing is jerky or smooth, and is probably best measured with pressure-sensing devices in the shoes. If you donít bend your knees when walking, you will send pounding shocks up your legs and back when they hit the ground.
Still, while walking, my guess is that the maximum force is only three times the usual weight they support (half of the body weight per leg -- itís shared between two legs) and not three times the total body weight. The time-average weight supported by both legs is just the total body weight.
When you run, the fraction of the time the feet are in contact with the ground decreases. In Olympic walking, the rules are that the athlete must not leave the ground at any time. This means that before one foot can be picked up, the other foot must be on the ground, making for a fraction of ground time for each foot greater than 50%, but as close to that as the walker can manage. When running, both feet leave the ground at times, and there is more bouncing, and thus more pounding force on the legs.
(republished on 07/12/06)