If you're interested in flatter abs and a stronger core, the plank is one of the key exercises you should be doing. Once the normal abdominal plank gets too easy, you've got a variety of options to make it more challenging, more interesting and more effective.

This is one of those options!

This is nice variation of the plank that involves dynamic transitions between two different plank positions...forearm and straight arm planks. The benefit lies in the moment of transition between the two positions.

You can do this type of dynamic plank on the floor, but I prefer to do it on a flat bench and a barbell set in the power rack (or another bar set at the right height, be it Smith machine or even the handle of another machine). I'll tell you why this is effective once I show you the exercise.

So first, set the bar a little above the level of the bench and set the bench about four or five feet away from the bar. Where you place it will depend on how tall you are...you'll need to adjust it to get the spacing right.

Set your forearms on the bench then hook your toes over the bar, keeping your body straight and stiff.

Now, the reason I use the bar is I find that when going the plank on the ground on the toes, it increases leg/hip flexor contribution to the stabilization of the core. When you hook the toes over, it takes some of that away and focuses more on the core for the stabilizing tension.

This will immediately make the plank harder to do.

The next step here is to transition to a straight arm plank.

Lean over onto the right arm then set your left hand on bench.

Straight out your left arm then set your right hand flat on the bench. At multiple points in this transition, you're basically planking on one arm.

Then just repeat on the opposite side, setting your left forearm on the bench while bending your right arm.

Now you're back with your forearms flat on the bench.

Repeat the maneuver until you can no longer support your body in the plank position.

Now, this one sounds simple but it's actually surprisingly tough to do. The transitioning with the majority of the tension go through one side while your toes are hooked over the bar instead of set on the floor puts a whole different tension on the core.

If you're new to the plank, this is not the version you should jump in and start with it. If you're already familiar with the plank, you're going to really enjoy this variation and how it targets the obliques and deep transverse abdominus muscles with the dynamic repositioning of the arms.

Great core training!