Most guys who are serious about fitness these days know that interval training is good for them. Cranking up the intensity for brief bursts makes you a better athlete and certainly makes for a more lively gym session than riding an exercise bike for an hour. But did you know that it's also one of the best things you can do to protect yourself from a deadly heart attack?

That's the implication of a recent study that's part of an important shift in the way the medical community thinks about cardio. Any of you still zoning out at the gym in front of CNN really need to get with the program. Athletes swear by intervals because they train the body to withstand the intense exertion of game conditions. Now cardiologists are swearing by them too, because they get the heart used to efficiently speeding up and slowing down like a finely tuned Porsche, a Porsche that will help you steer clear of a heart attack -- or survive a collision with one. In the study, published in the New England Journal of Medicine last year, French researchers measured the heart rates of 5,713 healthy men on exercise bikes, then followed them for 23 years to see which ones died of heart attacks. Of all the factors -- whether the guys were regular exercisers, how long and hard they could cycle -- the most telling was the ability of a guy's heart to rocket up through the rpms and then quickly return to a purring idle. In fact, those with the biggest ranges between their heart rates during intense exercise and at rest were four times less likely to drop dead of a heart attack than those with the smallest.

With this plan, from California performance coach Alwyn Cosgrove, you don't even need an exercise bike. Once your doctor has cleared you for intense exercise, test your heart responsiveness below, then start integrating the workout into your regular routine twice a week. Do Round 1 at a brisk clip without stopping. (It should take about a minute; if it takes much less, add a few reps per exercise.) Walk around for three or four minutes to catch your breath. Do Round 2, recover the same way, and repeat, pushing yourself even harder. Add a round a week, so you're doing five in the second week (three of Round 1 and two of Round 2), six in the third, seven in the fourth. After a month test yourself again and see how much you've reduced your risk of a heart attack.

FIRST ROUND
Standard Push-Up
12 reps
You know the drill: Assume the position, lower your chest to the floor, and push back up.

Body-Weight Squat
12 reps
Stand with your feet shoulder-width apart and your arms straight out in front of you or folded across your chest. Push your hips back, as if you are sitting down in a chair, and lower yourself until the tops of your thighs are parallel to the floor. Stand up and repeat.
 

Body-Weight Lunge
6 reps with each leg
Stand with your feet hip-width apart, step forward with your left foot, and lower your body until the top of your left thigh is parallel to the floor, then push back up to the starting position. Immediately repeat with your right leg, and alternate until you finish all your reps.

Bench Dip
12 reps
Stand with your back to a bench. Place your palms on the lip of the bench and extend your legs in front of you. (Only your heels should touch the floor.) Start with your arms straight and your butt just slightly in front of the bench. Lower yourself until your upper arms are parallel to the floor, or until your butt and legs are about to touch the floor. Push back up and repeat.

SECOND ROUND
T Push-Up
3 reps on each side
Do a standard push-up. At the top of the motion raise your right arm until it's straight up in the air and perpendicular to the floor. Return to the starting position and do another push-up, this time raising your left arm.

Diagonal Lunge
6 reps with each leg
Stand with your feet hip-width apart and your arms at your sides. Lunge 45 degrees to your left, push back to the starting position, then lunge to your right. Push back and repeat, alternating legs.

Step-Up
6 reps with each leg
Stand in front of a bench or step. Step onto the bench with your left foot, rising until your right foot is even with your left. Immediately lower your right foot to the floor, then your left. Repeat, stepping up with your right foot. Alternate feet.

Decline Push-Up
12 reps
Same as number one, but place your toes on a bench or step and end with your head lower than your hips.