We all know exercise makes you live longer. But this will actually get you off the couch.

When someone dies in the intensive care unit, the first thing the nurse does is turn off the EKG monitor. That’s because the heart can go on depolarizing — writing its electrical signature on the screen, if not actually pumping blood — for many minutes after everything else stops. It’s creepy, but touching, too. The heart is the soldier who can’t bear to surrender until long after the battle is lost.

Because the heart is the last organ to die, it’s no surprise that medicine has expended much effort to get it to live longer. What’s surprising is that the best strategy is to work it harder, not go easy on it. The ceaselessly pumping organ is happiest if you test its limits in a controlled fashion on a regular basis.

In other words, if you exercise.

Exercise requires time and tolerance for discomfort, and you can’t store it up. For that reason, it lags behind other behaviors that doctors, the government and our consciences tell us to do (or not do). Only 50 percent of American adults get at least 150 minutes of aerobic exercise a week, which is the current recommendation. Larger fractions of people aren’t obese (65 percent), get at least seven hours of sleep a night (65 percent) and don’t smoke (83 percent). Nevertheless, there’s no getting around the benefits of exercise. The evidence keeps piling up.

Over the past two decades, research has shown that exercise reduces the risk of heart attack, helps control weight, decreases inflammation, lowers the risk of developing diabetes and certain cancers, increases the chances of survival after a heart attack, lifts mood, slows the decline of sexual performance and prolongs independent living in the very old. “It’s really hard to find something that is not improved with exercise,” said Michael J. Blaha, a preventive cardiologist at Johns Hopkins Hospital and a researcher in the field. “Everyone can benefit from it. Even at higher age, when you’re at increased risk of dying, exercise is able to add time to your life.”

Small benefits that add up

Although many organs, and the body as a whole, are helped by exercise, the cardiovascular system — the heart and blood vessels — is helped the most. Many people think exercise’s principal benefit operates through blood lipids, the compounds that contribute to artery-clogging atherosclerotic plaques. In fact, exercise alone has only a small effect on them. Total cholesterol, LDL (the dreaded “bad cholesterol”) and triglycerides go down a little, and HDL (“good cholesterol”) increases. However, the dramatic improvement in lipid profiles that many first-time exercisers report is more an effect of weight loss than exercise per se. Instead, exercise’s action on the heart and the blood vessels is the sum of small benefits acting through many physiological pathways.

What goes wrong in our bodies when we park ourselves for nearly eight hours per day? A chain of problems from head to toe. CLICK IMAGE TO VIEW GRAPHIC

Exercise lowers blood pressure. It makes the body more sensitive to the action of insulin, which lowers blood glucose. It makes platelets — the mini-cells that trigger clots in strokes and heart attacks — less sticky, and increases the amount of clot-dissolving enzyme in the blood. It reduces some markers of body-wide inflammation, such as C-reactive protein. It slows the accumulation of calcium in arterial walls, a risk factor for heart attack. It increases the nitric oxide made by arteries, which allows them to expand and carry more blood when circumstances demand. Exercise also lowers the resting heart rate, which benefits the heart over the long run. Studies in lab animals show that moderate-intensity exercise has measurable and even visible effects on the heart.

The body loses muscle mass with age, and the heart, being mostly muscle, isn’t spared. (A 70-year-old man has roughly 30 percent fewer heart muscle cells than a man in his 20s.) Exercise slows the process. It reduces the rate at which cells are lost both through wear and tear and through the programmed process of cell death called apoptosis. Aging rats forced to swim an hour a day have hearts far younger-looking — less thickened and scarred — than their sedentary brethren.

On your feet

What it all adds up to is longer life. But it isn’t an all-or-nothing relationship. Instead, the more a person exercises, the more the risk of heart attack and premature death goes down. Only at extreme and prolonged exercise do worrisome effects appear, and even then there’s no evidence that such behavior shortens life. This “dose-response” relationship is apparent as soon as you get off the couch and do almost anything. It’s like a signing bonus.

A study of 221,000 Australians age 45 and older found that those who simply stood more than two hours a day had a death rate 10 percent lower than people who stood for less than two hours when followed over the course of four years. People on their feet for eight hours a day had a 24 percent lower death rate. If you walk instead of stand, the payoff, not surprisingly, is bigger. A study of 1,239 Japanese men recruited at age 64 found that those who walked at least two hours a day had half the chance of dying over a 10-year period as those who walked less than 30 minutes a day.

In general, the greater a person’s exercise capacity, the lower the risk of dying. That became clear when researchers looked at the experience of 33,000 people (with an average age of 57) who took exercise stress tests at the Henry Ford Health System in Detroit. Treadmills measured the intensity of their exertion in METs (metabolic equivalent of task). A MET is the ratio of energy expended during an activity to energy expended while sitting motionless. Working at a computer is 1.5 METs. Bicycling at less than 10 mph requires 4 METs, and very brisk walking requires 5 METs; both fall into the category of moderate-intensity activity. Playing basketball is 8 METs, and running at a 10-minutes-per-mile pace is 10 METs. They are considered vigorous-intensity activities.

In the 10 years after the stress tests, 41 percent of men and 23 percent of women who didn’t achieve 6 METs had died. However, for those who achieved more than 12 METs, mortality was only 3 percent for the men and 1 percent for the women. (All the patients in this comparison were taking statin drugs to lower their cholesterol). Fitness paid off, even among people unlucky enough to suffer heart attacks. A study published this month using the same group of patients found that the risk of dying in the month after a heart attack was 14 percent in the under-6-METs group but only 6 percent in the over-12-METs group.

“Your baseline fitness now predicts your survival of that first heart attack. That’s an important message,” said Blaha, one of the authors of the new study. Exercise’s ability to reduce a person’s chances of dying from cardiovascular disease extends well beyond the weekly 150 minutes of moderate exercise (or 75 minutes of vigorous exercise) currently recommended for adults. An analysis of data from studies in the United States, Europe and Taiwan found the mortality risk bottomed out when a person did nine hours of moderate exercise or 4.8 hours of vigorous aerobic exercise per week (roughly 3 1/2 times the recommended amount). At that point, a person’s risk of cardiovascular death was half that of someone who didn’t exercise at all.

So that’s the good news. The bad news is that exercise isn’t enough. You also have to stop sitting around when you’re not exercising. It turns out that sedentary behavior — defined as anything that takes less than 1.5 METs of effort — increases the risk of cardiovascular disease even if a person gets enough exercise. A study of AARP members who got at least seven hours a week of moderate-to-vigorous exercise found that over an eight-year period, people who watched at least seven hours of TV per day were twice as likely to die of heart disease as people who watched less than an hour. Other studies have found similar effects.

The average American spends more than half of all waking hours in sedentary behavior, principally commuting or sitting in front of a computer screen or television. There are no government guidelines on the matter, but some experts say 10,000 footsteps a day — the equivalent of five miles of walking — should be the goal. (That would more than satisfy the exercise recommendation if done briskly enough.)

Track your steps

Taking that many steps is virtually impossible in an indoor job, even with standing desks and walking meetings. Nevertheless, people can make headway with the help of devices that count steps and chart them by hour, day, month and year. “Tracking what’s happening is half the battle in pretty much everything that involves changing behavior,” said Haitham M. Ahmed, another preventive cardiologist at Hopkins. He advises his patients to use pedometers on wristwatches or smartphones, calling wearable activity tracking “a big breakthrough.”

So, if you don’t have one yet, there’s probably another screen in your future to obsess over, perhaps to better effect than Twitter and Instagram.

By David Brown for The Washington Post