If anyone is curious about the drawing book at 37:35, it's called Cours de Dessin (Drawing Course) by Charles Bargue
Edit: I got that book for Christmas after putting it on my Amazon Wishlist. It's fascinating!
This looks like it was a study done following the methods laid out in the Charles Bargue Drawing Course.
Here's the book on amazon https://www.amazon.com/Charles-Bargue-Drawing-Gerald-Ackerman/dp/2867702038
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I'm not sure of the exact terminology, but you'd basically do a simple lay-in (like a simplified version of the body), heavily measured from your reference. Then you go in and add or remove shapes making the forms more complex.
The process would be similar to this but on a larger scale: https://cdn.shopify.com/s/files/1/0319/2345/files/bargue_2_large.jpg?589
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Hope that helps.
I don't know anything about either of these courses except one is free and the other is subscription; no idea if complete or not. I was hunting for the book.
https://www.amazon.com/Charles-Bargue-Drawing-Gerald-Ackerman/dp/2867702038
https://www.scribd.com/doc/316611362/Charles-Bargue-Drawing-Course-pdf
https://charlesbarguedrawingcourse.com/courses/
I didn't have this book or course but did the next best thing: used sculpture as models. You have untold resources on museum websites; Classic Roman and Greek sculpture. Particularly marble lends itself to rendering value correctly.
Charles Bargue http://www.amazon.com/Charles-Bargue-Jean-L%C3%A9on-G%C3%A9r%C3%B4me-Ackerman/dp/2867702038
Godfried Bammes "Die Gestalt Menschen" http://www.amazon.ca/Die-Gestalt-Menschen-Gottfried-Bammes/dp/3862300013 or Der nackte Mensch