One way to maintain a healthy weight is to stay physically active. But sometimes you say to yourself, "I just don't have time."

Oh, yes you do. The secret: HIIT.

HIIT, or high-intensity interval training, alternates between bursts of max effort and brief rest periods, generally between 10 and 30 seconds. HIIT workouts usually involve several rounds of a defined series of exercises.

The idea is to concentrate your efforts into a workout that's both effective and short enough to easily fit into your day. Most HIIT routines don't last longer than 30 minutes, and many (such as the one shown below) are much shorter than that.

"Despite how short the workout is, it can produce health benefits similar to twice as much moderate-intensity exercise," says Grant Tinsley, PhD, of Texas Tech University.

The following workout should last roughly seven minutes. After each exercise, rest for 10 seconds. Do two rounds of the complete set. (See your healthcare practitioner before starting a HIIT-based fitness routine, especially if you have a pre-existing condition.)

High Knees (15 seconds)

Stand with your feet hip-width apart. Lift your left knee up to your chest, then your right knee. Keep moving at a sprinting or running pace.

Pushups (10)

Start on the floor: hands next to shoulders with fingers splayed, arms extended with a straight back and up on the balls of your feet. Engage your core, then bring your chest down toward the floor, keeping your back straight, before rising again. (Do pushups from your knees if you don't have sufficient arm strength.)

Jump Squats (10)

Stand with your arms at your sides, feet hip-width apart. Pull your shoulders back and down without arching your low back, then shift your hips backward and downward to bend the knees. Lower yourself until your heels are nearly lifting away from the floor. Pause briefly, then then jump upwards in an explosive motion as you extend your knees, hips and ankles.

Crunches (10)

Lie down on your back with your feet on the floor, hip-width apart, and bend your knees so they're facing the ceiling. Then place your arms across your chest, contract your abdominal muscles, inhale and, using your core, slowly lift your body up to your knees and exhale. Inhale on your way back down and return to the starting position.

Triceps Dips (10)

Sit on the edge of a chair with your legs straight and together, and place your hands next to your hips, fingers around the edge. Then tighten your abs, straighten your arms and lift yourself up, moving forward until your weight is supported by your arms. Keeping your hips close to the chair and your elbows close to your body, slowly lower yourself until your upper arms are parallel with the floor before slowly straightening your arms and returning to the start position.

Lunges (5 each side)

Stand up straight, then step forward and down with either leg into a 90-degree bend while keeping your upper body straight. Do not let your knee travel forward of your toes.

Mountain Climbers (15 seconds)

Get into a plank position and pull your right knee into your chest, then pull that knee out and your other knee in. Keep rotating sides and focus on bringing your knees in and out as far and as fast as you can.

Side Planks (15 seconds per side)

Lie on your side and place one leg on top of the other. Then lift yourself up on one hand (you can also use your elbow instead of your hand if you need to).

Jumping Jacks (15 seconds)

Stand up straight, legs together, arms at your sides. Then, bending your knees slightly, jump up, spreading your legs to roughly shoulder-width apart while stretching your arms out and over your head. As you land, return to the starting position.

Planks (15 seconds)

Assume a high pushup position, placing your hands under your shoulders with toes on the floor. Squeeze your glutes and focus on the floor for stability, keeping your head in line with your back.