Why a person leans forward when pushing a heavily loaded pushcart?

Answer 1

In order to push something forward, you have to push backward on the ground. If the object isn't very massive, then you don't need to push too hard against the ground, but the more massive it is the harder you have to push.Leaning forward comes from the physics of how your body operates. The way your muscles and joints work, you can exert more force "up" (along the length of your body) than you can "sideways" (perpendicular to the length of your body), because pushing "up" lets you use most of the large muscles in your legs while the "sideways" force comes mostly only from the muscles that rotate your leg at the hip joint. Leaning allows you to use some of that greater capacity to push "up" in a sideways direction.