It's really fascinating. It's written in 1904 and rails against the problem of obesity and a general lack of good health. His solution is to do 15 minutes worth of exercises each day to help promote good "core health" (abs/back, organs, skin). It's kind of crazy that we're still dealing with the same issues today.
So, Jessi and I have been doing the exercises this week. My core is definitely sore! We'd like to keep it going as long as possible... we'll see... We do skip the bath in the middle and just take a shower at the end. Since we're just starting it takes us around 25 minutes, but it will easily be shorter once we have all 18 exercises memorized.
Since the book is free, I recommend downloading and checking it out. It's only 15 minutes.