Well, HIT has come in A LOT of different guises over the years but I think that Mentzer’s original ideas for Heavy Duty were pretty good. Most of us are gym rats anyway so we can’t really stand his more recent recommendations of training once every 9-12 days. Bascially you work using pre-exhaustion and work to failure in a 6-10 rep range. That’s it. So a program would look something like this:
MONDAY - chest/delts/triceps
Incline flyes/incline presses
WEDNESDAY - legs
Leg curls/stiff leg deadlift
Shrugs/bent over row
Barbell curl/supine grip pullup
Now, Mentzer recommended a few warmup sets (‘no more than necessary’) and then one all-out, balls-to-the-wall, “if you’re not dying you’re not doing it right” set. Rep cadence is fairly slow and deliberate and you make sure you get a full ROM on each rep. That’s a basic HIT program from the old days.