The drawings above is based on examples in the book (referenced below) on a lesson about human proportion. If you're an art student, you probably already know about the whole "8-heads proportion" idea. I learned about it in another video I watched a few months ago but at the time I didn't really take it that seriously. Now, I've finally put it into practice.
The video above is done by a guy named Shoo Rayner, by the way. I highly recommend you subscribe to his YouTube channel if you're interested in learning how to draw or simply like videos of other people drawing. I've learned a lot from his videos and they're fun to watch too.
Barrington Barber 2015. The Fundamentals of Drawing: A Complete Professional Course for Artists, pp 34-35.