Some fitness fads come and go (we see you, Shake Weight), but others, like yoga or Pilates, aren't going away anytime soon. Another trend that's definitely here to stay? High-intensity interval training, or HIIT, which involves short bouts of extreme effort alternated with periods of rest. "HIIT workouts are quick and dirty, never lasting more than 30 minutes including a warm-up and short cool-down," explains Gina Harney, certified personal trainer and creator of "You're working as hard as possible for a short amount of time and then reaping the rewards throughout the day."

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While there's no such thing as a fitness miracle, HIIT workouts come pretty darn close. Research suggests that HIIT can super-charge fat burning High-Intensity Intermittent Exercise and Fat Loss. Boutcher, S.H. Journal of Obesity, 2011; 868305. , boost metabolism Metabolic Profile of High Intensity Intermittent Exercises. Tabata, I., Irisawa, K., Kouzaki, M., et al. Medicine & Science in Sports & Exercise, 1997 Mar;29(3):390-5. , and improve cardiovascular fitness Six Sessions of Sprint Interval Training Increases Muscle Oxidative Potential and Cycle Endurance Capacity in Humans. Burgomaster, K.A., Hughes S.C., Heigenhauser G.J., et al. Journal of Applied Physiology, 2005 Jun;98(6):1985-90 . Plus, the vigorous nature of HIIT ensures you'll continue to torch even more calories for hours after your workout ends. Bottom line: HIIT is quick, effective, and the perfect way to train for anyone who's short on time and wants to see results stat. (And who isn't and doesn't?)

Intrigued? Get started with this exclusive upper-body workout for women from Harney's new book HIIT It! In less than 30 minutes, these highly effective circuits will target and strengthen every muscle above your waist. All you need is a set of medium-weight dumbbells and your own bodyweight.

To warm up, perform 5 minutes of moderate cardio (such as jogging, jumping rope, or cycling). Complete 3 rounds of circuit 1, then rest for 30 seconds to 1 minute. Boost your heart rate again by running or walking 1/4 mile. Then complete 3 rounds of circuit 2, followed by a cool-down stretch—and you're done.

Upper-Body Workout: Circuit 1

1. Overhead Press

12 reps
Overhead Press

Hold a set of dumbbells and create 90-degree angles with each arm so upper arms are parallel to the ground and dumbbells are at about head height. As you exhale, press the weights overhead (without clanking the weights together). Return to the starting position, not letting elbows droop below shoulder height to keep some resistance.

2. Triceps Kickback

12 reps
Triceps Kickback

Hinge forward from your hips, keeping core tight and flat back. Bending elbows, glue your upper arms to your sides. On an exhale, straighten your arms as much as possible. Inhale to bend elbows back to starting position. Be sure to maintain a neutral spine and neck position.

3. Chest Press

12 reps
Chest Press

Lie faceup on a mat. Bring elbows out in line with shoulders to create a 90-degree angle. Press the weights up without clanking them together, focusing on engaging the muscles in your chest. Lower weights back to the starting position.

Upper-Body Workout: Circuit 2

1. Side Plank With Lateral Raise

12 reps per side
Side Plank with Lateral Raise

Start in a side plank (either full or modified by keeping your bottom knee on the floor) and hold a light dumbbell in your top hand. Bring weight in front of the center of your core. Keeping your arm slightly bent, lift weight up to shoulder height. Return to starting position. For even more of a challenge, you can lift your top leg and touch it to the weight between each rep.

2. Push-Up

15 reps

Start in plank position with hands planted directly under shoulders (slightly wider than shoulder-width apart). Ground your toes into the floor to stabilize the bottom half of your body. Keeping your spine straight (don't lift hips, and keep neck in line with your spine instead of dropping it forward) and knuckles pressing into the floor, lower your body until your chest almost grazes the floor. Exhale as you press back up.

3. Triceps Dip

15 reps
Triceps Dip

You can perform these on a bench (hands on the bench, feet on the floor) or on the floor. Point your fingertips toward your toes and bend your elbows, making sure to keep your hips lifted. Straighten your arms by engaging your triceps. For an added challenge, straighten your legs, balance on only one leg, or place a flat weight on your lap.

The Quick and Dirty Upper-Body Workout
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