ACE curriculum needs improvement
I just completed the ACE certification. A friend and I studied together, and we were both able to pass the exam after about 3 weeks of study.
However, we both felt the curriculum was terrible. There are 2 textbooks, and most of the chapters are written by different authors. As a result, there is a great deal of repetition from chapter to chapter, as well as a number of inconsistencies. There is also a painful degree of verbosity and unnecessary padding in the material -- so much so that my friend and I began to suspect that the authors must have been paid by the word. With a decent editor, the text could easily have been cut in half.
After slogging through that frustrating curriculum and completing the sample tests ACE sells at its web site, we sat for the real exam. We were both surprised to encounter a number of questions on material that we had absolutely never seen in our textbooks. In other cases, answers resembled but did not quite match what the texts had taught, or they used metrics (such as VO2max) that the textbooks and sample tests had de-emphasized. Moreover, some of the multiple-choice questions were so vaguely or strangely worded that answering them was more a matter of mind-reading than knowing the course material. Lastly, the 2 multi-part simulation questions were apparently developed by someone who never read those umpteen long-winded chapters about the ACE "Integrated Fitness Training" model in the textbook.
In sum, the curriculum was of such poor quality that it made mastering the material needlessly difficult and unpleasant, and the exam did not accurately reflect either the content or the emphases of the curriculum. Due to this mismatch, I could have studied the textbooks for 6 months (not an appetizing prospect, by the way) and still would not have been significantly better prepared for the exam. So if you go with ACE, be prepared for some frustration!
I have no firsthand knowledge of any of the other personal-trainer certification programs, but I find it hard to recommend ACE. They've tried to dress up their program with a scientific veneer and a trademarked acronym or two, but ultimately they feel like a wannabe to me. They're not inexpensive, either, and I'm not sure you get enough reputational "bang" for the buck.