This workout routine is designed after the U.S. Marine Corps’ combat-conditioning program presented on Men’s Health. The title says “Marine”, but one secret to staying in shape means learning to mix up your routines. The general idea of fitness is keeping your body guessing.

If you have been on Stew Smith’s 20-minute routine for a while (say, 2-4 weeks), it’s time to switch to a workout that will give your body a different challenge. The different challenge prevents your body from adapting as it gets used to performing repetitive movements from the same workout routine for a long period of time. Adaptation is good, but once your body has adapted, its time to introduce new stresses.

Think of your body as a set of gears in a car. After running on first gear a bit, the speed remains constant until you shift to second. When your body is not introduced to different or even more challenging stresses, your gains start to slow down, and you eventually end up at a certain fitness level. This is known as a fitness plateau.

Like any new fitness routine, make sure to follow the plan indicated to gradually prepare physically and mentally for the demands of this new fitness program.

The workout routines suggested in Men’s Health are to be performed 3 times a week, assigning a day of rest in between sessions. It is also suggested that you start your routine with core-specific exercises, particularly non-moving exercises such as planks and side bridges.