U.S. troops keep up with their training even when they’re deployed to areas where they have nothing to work out with but the ground beneath them.

If the lack of a gym membership and equipment is the excuse you’ve been using for avoiding workouts, let this plan—designed by a 20-year Marine—set you straight.

How it works

Basic exercises like the leg raise and flutter kick will never die. Partly because they can be done anywhere, but mostly because they work. Unfortunately, they also burn. Working with higher reps and holding uncomfortable positions for time will condition your abs along with your heart, and may toughen you up mentally, too.

Directions

Perform the exercises as a circuit, completing one set of each in sequence without rest. Afterward, rest 60 seconds, and then repeat the circuit once more.