Caveat: I didn't read the book and I'm not an expert. For me it doesn't make any sense. 4 hours a week is simply not enough for your body. According to some study even 30 min. a day is not enough. Just sitting 8+ hours a day has deleterious effects that exercise cannot make up for:

http://mashable.com/2011/05/09/sitting-down-infographic/

EDIT: If you want to live healthy it's really about changing the whole lifestyle, including dieting and the way you work(standing desk!). Just 4 hours a week won't cut it.