Morphological signs that allowed a person to master upright walking?

The man was not always upright. Our ancient ancestors used to move the hand. Then the hands were used as an aid to locomotion. Gradually, the person acquired a straight posture. Walking upright became possible due to several factors. The first is the curvature of the spine at four locations. This allows us to reduce the stress on the back when walking and working. The length of the lower limbs also plays an important role. Also, our feet are not flat, but curved, which also reduces the load on the ridge when walking.