Original 531 Challenge, Page 173 Forever

Anyone try this? It looks like an awesome way to get lifts up quick.

I have a question about the sets though. For the sets, it says “3x5,PR set” Is the PR set done as the last set of five, or is it an additional set?

It would look like this:
65% x 5
75% x 5
85% x 5 or more reps (a good goal if you set your training max properly is 10)

As Assault says
Except the last 85% set when it is a PR set, you try to beat your previous best with that weight.
So if last time you got 10 reps with 100 you try to get 11 reps.
Or if you are a little beat up, knowing you are not going to get 10 reps, you set your PR set before the lift. Saying I want to get 9 reps. Then 9 is the goal.
But try to beat your previous rep record at that weight.
There is a little difference between a AMRAP set and a PR set.
AMRAP is taken to failure, PR is just beating a previous rep PR or a goal in mind before the set. PR could be an AMRAP (for me it often is) but not necessarily.