PDHPE only overlaps slightly with Bio during Prelim, and even then it's just the names of muscles and bones, which don't apply to the actual HSC at all.
Funnily enough, PDHPE overlaps A LOT with Biochemistry of movement (an elective in Chemistry!), with the energy systems and whatnot.
Technically, PDHPE is a branch of science, but not as hardcore as Chemistry, Physics, or Biology. It's considered a social science, which I suppose means it's not AS difficult as the aforementioned sciences.
But yes, it is like other sciences in some aspects, Chemistry in particular. That being said, I find it a highly enjoyable subject and if you can get past the muscles/bones, you should be okay. It's a good subject.
I hope that cleared some things up for you! C: