Air Force Basic Training!

A plank is getting into a pushup position but hold it and tighten your abs in the process. Plus make sure your arms are under you or as if you are doing tricep pushups. If your recruiting station has "pt" and some do, GO. This will kinda give you an idea of what is to come. I run with a 20lbs weight vest but thats just me.

If you find the planks with arms extended difficult at first you can also do them on your elbows (same effect just a bit easier on the wrists). Start at 30 seconds and increase by 15 second increments as your body adjusts.