First, some not-so-shocking but slightly reassuring news: a whopping 76 percent of Americans aren't getting enough aerobic and strength-training exercise. This is according to the latest data from the Centers for Disease Control and Prevention. The report states that less than 25 percent of U.S. adults currently meet the requirements set by the US Department of Health and Human Services: at least 75 minutes of vigorous activity or 150 minutes of moderate activity per week, plus muscle training at least twice a week.

But here's the good news: if you're a fairly active guy, you likely only need a few days of training to ensure you're hitting that goal. And if you're looking to target your midsection (and honestly, who isn't?), then this workout aims right at the core. If you want shredded six-pack abs, experts agree that you need to limit your carbohydrate intake, get plenty of sleep and minimize stress. And while you can't spot reduce fat, you can focus your workouts to target muscle groups that can help sculpt and tighten your midsection, while helping your inner washboard shine through.

It's important to remember that there's more to abs than just sit-ups. These three simple moves will translate to a slimmer, more defined stomach—not to mention a stronger, more stabilized core. They also require no equipment, which means you can do them in your bedroom, at the park or in your hotel room.