You don't have time for endless cardio, and it doesn't seem to work for you any more anyway. Hours in the gym with a personal trainer isn't in the cards either. There's got to be some way to get a lean body, flatten your abs, and add a little muscle without giving up on having a life. There is: It is called HIIT.

What the Heck is HIIT?

HIIT stands for High-Intensity Interval Training. This kind of workout involves cycles of short, high-intensity exercises, followed by short recovery periods. When you work out this way, your heart rate continually varies, going from a relatively low level to near your maximum, then back down again. HIIT workouts are tough, but short.

A basic workout will involve a warm-up period, several cycles of high-intensity work, and a cool down period. The whole workout will usually take less than an hour and should be repeated no more than 3 times a week to allow your muscles to recover between workouts.

Some programs incorporate a short abs workout at the end of the session (before the cool down phase) for those looking to specifically build great abs. One example of such a program is the HIIT-based The Truth About Six Pack Abs (HIITSixPackAbs) which combines whole-body exercises, specific abs exercises, and a filling, natural diet into a comprehensive fitness program.

Compare the HIIT approach to more traditional approaches that feature fun things like jogging for hours, swimming endless laps, and heavy dieting. Short intense workouts are certainly more fun and more likely to fit into your busy life.

But does HIIT work?

In recent years, several scientific studies have shown that short, high-intensity workouts are more effective for losing fat while maintaining muscle mass than high-volume, lower intensity aerobic work-outs like jogging. This is true even though your body burns fat most efficiently during those aerobic workouts.

With HIIT, your body burns more calories between workouts due to the higher metabolic rate triggered by the high-intensity workouts.

What is a HIIT Program Like?

At this point, you're probably wondering what a HIIT program is like. Well, they vary depending on who designed the particular program, but they generally have some characteristics in common. In particular, they usually involve multi-joint movements.

That is, you do exercises like deadlifts that involve multiple muscle groups, instead of curls, which involve a single muscle group. Involving multiple muscle groups in each exercise really cranks up the intensity while allowing you to get a lot done in a short time.

Perhaps the ultimate HIIT workout is sprinting. A sprinter's frequent short bursts of maximum effort followed by rest periods is high-intensity interval training in a pure form. And if you've ever looked at the physiques on sprinters, you've seen what this kind of training program can do for you.

More and more, short, high-intensity workouts are being recognized as the best way to get in shape, tone your body, strengthen your heart, and burn fat. If you want to be fit and lean by summer, with a flat belly, solid muscles, and a healthy heart, try a HIIT workout program.