It really is, and a while ago I had seen another article where they were doing a 100 swings a day and after 2 weeks on top of my normal training schedule I was hurting. Dan has gone and multiplied that by 5. FYI anything he says make sure you understand how monumentally hard it will be from the get go and do the challenges as he wrote.
I'm trying this out. I've been ulc for three weeks, but after the first day of this work, I realized that carb backloading is a must. I went small and just added a potato and a little rice with dinner. My body sucked those carbs right up and this morning, I'm still in Ketosis despite 100 or so grams of carbs.