I listened to it as an audiobook. It's a decent pop science book. Focuses on the physiology and psychology of feats of athletic endurance. It mainly focuses on running (long distance) and cycling, which is not too surprising since these sports are well studied. Trekking, both in cold and heat, free diving, mountain climbing, and a few other feats of endurance also make appearances.

The author is runner, and seems to be from Ottawa or at least has run the Ottawa marathon which neat. The author is definitely a good runner based on his half and full marathon times

While I said the book was about  psychology, it's more about mechanical brain-body connections than beliefs, although those are addressed also. My biggest takeway is that my brain is automatically processing signals from my body in the background in a sophisticated way, then presenting this information in a manner that can be a bit crude and make it hard to understand exactly what is happening in my body. Also, a lot of the regulation is anticipatory, rather than immediate feedback on current state. For example, swishing a sports drink in your mouth can improve performance, even if you don't swallow, probably because of detection of carbs. Also, don't need to overdrink. Your body is complicated, and even if you lose some water weight, doesn't mean that you're dehydrated to point of impeding health or performance.