Hi! Sorry for the delay but I'm rather new to this and hadn't checked back on topics I had replied to. CPK levels are the reading that comes from bloodwork that indicated if there is tissue damage in the muscles. Usually if it is high, it could indicated that one has had a heart attack. My reading was around 800, normal is under 100 but mine was (most likely) from running a 1/2 marathon in October and again in May. So all the training ruined me. I haven't run since, I'm too fatigued If you aren't aware, we do not heal well because of our sleep disorders (no REM stage means NO healing). Anyhow, if your friend worked out with weights or had some vigorous workout prior to the bloodwork that too work create a high reading. I hope this helps! If you have any other questions, just ask!