If the most exercise you did today was walking from your office to the cafeteria to get lunch, you're not alone: According to a survey from the United Health Foundation, 26.2 percent of Americans haven't gotten off their butts outside of going to work in the past month -- up from 23.9 percent a year ago.

There's no sugarcoating it: That's bad. Being inactive kills as many people a year -- by increasing your risk of heart disease, type 2 diabetes, and cancer -- as cigarette smoking, according to a 2012 study in The Lancet.

We understand if you're pressed for time and can't afford a daily trek to the gym, but here's the thing: A good workout doesn't have to be an hour long. In fact, the majority of gains from exercise come in the first 20 to 30 minutes, and at the right intensity, they come within the first 10, BJ Gaddour, C.S.C.S., metabolic training expert and creator of the Speed Shred DVD series, tells MensHealth.com.

And if all you've got is 4 minutes to spare? That's OK, too. Follow these three routines for optimal results -- no matter how much time you have:

4 Minutes
Follow the Tabata protocol, an interval routine developed for the Japanese Olympic speed skating team. Do 20 seconds of maximal effort in one muscle group (think: pushups) and rest for 10 seconds. Repeat with a non-competitive exercise (like squats) and rest for 10 seconds. Repeat for a total of 4 minutes. According to a study by Japanese researchers, this 4-minute workout can boost your aerobic fitness by 14 percent.

What's more: It could also boost your anaerobic capacity -- a measure of how long you can exercise at your highest intensity -- by 28 percent. Pro tip: Minimize cross-fatigue by alternating between non-competitive muscle groups like upper and lower body, Gaddour suggests. (Need more of a challenge? Follow along with Gaddour in the new DVD series from Men's Health, Speed Shred.)

10 Minutes

Blast through a bodyweight circuit before breakfast, but keep it short: Ten minutes of intense circuit training provides the same all-day fat-burning results as a 30-minute-long circuit of the same intensity, Gaddour says.

Do this:
20 Jumping Jacks
12 Prisoner Squats: Stand with your hands behind your head, your chest out, and your elbows back. Sit back at your hips and bend your knees to lower your body as far as possible without losing the natural arch of your spine. Squeeze your glutes and push yourself back up to the starting position with your legs.
15 Pushups
12 Forward Lunges with each leg
10 Stickups: Stand with your back to the wall and feet about 4 inches from the wall. Place the back of your arms against the wall, with upper arms parallel to floor and forearms at 90 degrees. Raise your arms overhead while keeping them against the wall at all times. Slowly return to below the starting position, tucking your elbows into your sides and bringing shoulder blades together.

Rest for one minute between sets, and repeat as many times as you can before the time's up. For more new exercises from the country’s leading experts, sign up for the Men's Health Exercise of the Week newsletter.

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15 Minutes
Tweak four muscle-building standards to carve your core. According to research published in The Lancet, 15 minutes of exercise five times a week can add three years to your life by cutting your risk of developing cancer. Try this quick upper-body workout that also really hits your abs.

Do 10 reps of each of the following moves, rest for a minute in between sets, and repeat for a total of three sets.

Chinups with Knee Raises: Hang from a chinup bar using a shoulder-width, underhand grip. Pull your chest to the bar while also raising your knees to your chest. Pause, and slowly lower your body while also lowering your knees. If you can't complete a chinup, simply raise your knees while hanging from the bar.
Standing Single-Arm Shoulder Presses: Stand holding a dumbbell just outside your shoulder, with your palm facing you. Set your feet shoulder-width apart and keep your knees slightly bent. Raise the weight until your arm is completely straight, and then lower it to the starting position. Do 10 repetitions with each arm.
Pushups with Row: Start in a pushup position as you grip a pair of hex dumbbells placed shoulder-width apart, your palms facing in. Lower your body, pause, and push yourself back up. Now pull the dumbbell in your right hand straight up to the side of your chest. Pause, and lower it. Repeat the move with your left arm.
Lying Tricep Extensions: Lie faceup on a bench with your feet flat on the floor. Hold a pair of dumbbells at arm’s length above your head, your palms facing each other. Without moving your upper arms, bend your elbows to lower the weights until your forearms are past parallel to the floor. Pause, then lift back to the starting position.

For more get-fit-quick workouts, test yourself with one of the Men's Health Train for Life Challenges.

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