Tren puts a strain on your cardio system, which will be stained already if you were 17% fat or higher however electronic body fat scales are notoriously inaccurate so it might not be that high, basically if you don't have at least a very visible four-pack you're too fat to be on cycle, Tren also has the ability to produce nasty sides related to raised prolactin, which is the hormone responsible for making your dick go limp after ejaculation, some users, typically those who don't run caber or prami on cycle and/or use nolva in their PCT (which exacerbates this issue) experience long term erection and/or libido problems as a result of this...