Re: Anyone taken the ACSM - HFS certification test?
I am both CSCS and HFS (it was HFI back when I took it). I thought the ACSM HFI was more difficult than the NSCA CSCS exam. As far as studying for the CSCS, I used the Essentials of Strength and Conditioning text and hands on experience.
For the ACSM HFI I took a course in grad school that somewhat prepared me for the test. I also used a text entitled the Health Fitness Instructors Handbook (I think) as well as the ACSM's Guidelines for Exercise Testing and Prescription. Also, be sure to practice hands-on testing. You will have to take heart rate, blood pressure, skin caliper measurements, etc. You do this on human subjects usually undergrad or graduate volunteers.