Source:  When you walk across level ground, the force on your knees is the equivalent of 1½ times your body weight. That means a 200-pound man will put 300 pounds of pressure on his knees with each step. Add an incline and the force is greater. The force on each knee is two to three times your body weight when you go up and down stairs, and four to five times your body weight when you squat to tie a shoelace or pick up an item you dropped.