The plank is a classic ab
exercise. Simple...uses just bodyweight...very effective.
If you haven't seen it, basically lay flat on your stomach
on the floor then hold yourself up on your forearms, keeping
your body straight like a plank.
Now it's time to kick it up
a notch, because you know me...I'm all about taking the
easy way out and doing things like a "normal"
person...
RIGHT!
Basically, you're going to
do a plank but with a weight dip belt hanging off you for
added resistance.
Naturally, you can't do this
off the ground - you'll need to do it in a rack or between
two benches - either way is fine.
Set the rails of the rack
a couple of feet off the ground. I like to put a towel over
the rail that I'll be putting my forearms on. Load up a
dip belt with a plate or two (I'm using a two 45-lb plates
in the demo here) and get it around your waist.

Now here's the trick...hike
the belt up so it's not on your waist but about mid-back.
This is easier on the lower back for this exercise - it
places the weight in a better position for the abs to work
against.

Reach up and back with one
leg and hook it over the rail.

Get the other leg up and on
the rail. You'll notice I'm not completely board straight
in this position. The demands of adding extra weight mean
you should bend your knees a bit so that they're not locked
out and taking all the stress into the knee joints.

Now just hold yourself in
that position for as long as you can, keeping your abs and
entire core area VERY tight.
When you can't hold yourself
up anymore, just set one leg on the floor, then other and
stand up. All done!
This one works great for
building core strength. It's the abdominal plank times 10.