Ever wonder why so many people have back problems later in life, even if they aren't overweight? Our bodies are not ideal for upright walking in the slightest.
Also, consider the ostrich, an organism will millions upon millions of years of evolution contributing to bipedal movement than humans. They have less than half the number of bones in their feet than humans do, and they are far more rigid. All our extra bones just make it easier for the arches in our feet to wear down, resulting in pain when walking. It makes sense that they are there, since our ancestors had prehensile feet that utilized the extra mobility of these bones, but it would make 0 sense to design a bipedal organism this way from scratch. Our feet are a painful in between, being neither ideal for grasping nor ideal for running.