In his second book, The 4-Hour Body he claims to have recorded every workout he has done since his late teens. Along with a variety of fitness and weight loss methods he has studied, his workout records are the basis on which the book was created. Of the over-abundance of authors nowadays who claim to have discovered the latest and greatest workout / diet secrets, Tim Ferris has years of data and testing to back his discoveries. He notes specifics when needed and his claims are in no way outrageous.
Even though Ferris has no medical or biology background, as a reader you find yourself wanting to believe him. His matter of fact way of explaining the information presented allows you to understand both the background and the “why” of what he is reporting. He also practices what he preaches. Throughout the text he gives real life examples of how to perform the exercises he teaches. There are also virtually no start up costs to anything in the book as well.