Seems to me that the quotation below gets to the core of that author’s concerns / objections. Sports scientists are great at finding underlying mechanisms and evidence for why certain adaptations occur or why certain stimuli are beneficial. Coaches tend to be much more interested on figuring out whether something works, not why it works.
Concern number one is that the authors provide no reference for this data so that the efficacy of the testing could be checked. One has no idea if these data were ever peer-reviewed by experts or if the data are published. Using unpublished data is not appropriate for supporting generalized conclusions published in a book. Concern number two centers around the relevance of cross sectional data on individuals to any generalized advice. Without an understanding of many other factors (some confounding) that will influence the results shown, these data really have no scientific basis. They are cherry-picked graphs used to support a point being made in the text- something that is not acceptable. Use of representative peer-reviewed data from published references is the only acceptable alternative and even this type of data can be very deficient in this field of study. Without longitudinal data as well as data on individual enzymatic profiles (profiles which are temporal) there is no ability to put any generalized interpretation on what is presented. This is not to say that the arguments presented by the authors cannot be supported, just that they do not provide the appropriate references to peer-reviewed publications- an unfortunate oversight.