How much exercise do you need to increase to your chances of surviving if you have a heart attack? A higher level of fitness improves the likelihood that you’ll live and may help cut the risk of heart attack in the first place. Yet only 20 percent of Americans know how long they need to swim, walk or practice yoga every week to save their lives, according to a new study.

The magic number of minutes for moderate activity is only 150 minutes a week. Take just 22 minutes out of your busy day to walk, and you’ll meet researchers’ recommendations. The same protection is afforded by 75 minutes of vigorous activity. Jog for 11 minutes every day, and you’re covered. Mix up your exercise routine with some combination of vigorous and moderate if you get bored.

Those are the findings from research that appears in Mayo Clinic Proceedings conducted by the Henry Ford Health System in Detroit and Johns Hopkins in Baltimore.

What’s stopping us from putting in the effort that could help us live longer? The answer is work for 41 percent of those surveyed in a study conducted by the Cleveland Clinic.

Another 37 percent said fatigue is getting in the way, and 28 percent said spending time with family and friends keeps them from exercising.

If you think those excuses are used by a tiny fraction of Americans, consider this: 40 percent of the population does not put in the recommended moderate aerobic exercise time of 2.5 hours a week.

The Henry Ford Health System in Detroit and Johns Hopkins in Baltimore investigators looked at 2,061 adults who had a first heart attack after taking an exercise stress test. An average of six years elapsed between the stress test and the heart attack.

Getting fit before the heart attack helped protect people after it happened. The researchers measured their subjects one month, three months, and one year following the attacks. Fewer than half of those studied were women. The ages of most was early 60s.

Those with heart disease need to get the same exercise as those who do not, but only one-third of Americans understand that, according to the Cleveland Clinic study. Cleveland Clinic researchers found those who exercise saw a 50 percent reduction in chances they will develop heart disease. Those who suffered from cardiac problems saw a 30 percent to 50 percent reduction in their risk of dying if they were active in a cardiac rehabilitation program, researchers said.

The Cleveland Clinic researchers recommend 30 minutes of exercise each day most days of the week if not all. They say that is a minimum, and they point out that the more you commit to exercise, the more benefit you gain.