How am I doing?

That’s a natural question when it comes to health and fitness, especially for men and especially as we age. You want to know whether all your hard work is paying off, or how far you have to go to catch up. And if you’re just starting to work out, you’re interested in how much effort you need to invest to improve and maintain your health.

Experts say there are reliable norms, advice that is solidly based on research and testing, but they recommend that you use the information with caution.

“Age and gender-predicted standards always give you a template to work toward. It lets you know where you are in terms of your fitness level,” said Jonathan Myers, a clinical professor of medicine at Stanford University and a health research scientist at the Veterans Administration Palo Alto Health Care System. “The ‘but’ is that you benefit from exercise without getting too caught up in where you are relative to a standard, without getting too compulsive about measuring your heart rate.”

If there’s one measure you should pay attention to as you get older, it’s your cardiovascular fitness. Here’s why: Numerous studies have proved that it is the single best predictor of mortality from any cause, not just diseases of the heart, lungs and circulatory system.

Men's health: What is fit for your age?

Cardiovascular fitness also improves quality of life — think fatigue, back pain or the inability to climb stairs or do yard work. Best of all, most of the benefits come when you switch from little or no exercise to a regular program. Or, as health experts put it, when you move out of the bottom two quintiles and into the middle.

At the Cooper Clinic in Dallas, doctors have been collecting data from tens of thousands of patients they have pushed to exhaustion in treadmill tests since 1970, producing one of the largest databases of cardiovascular information in the United States.

“We found that just 30 minutes of cardiovascular activity three to five times a week decreases chances of dying from any cause at all by 58 percent and increases longevity by six years,” said Tyler Cooper, chief executive officer of Cooper Aerobics Enterprises. Just moving from “poor” or “very poor” to “fair” on the Cooper scale conveyed most of that benefit, he said.

In fact, cardiovascular fitness is such a reliable predictor of good health that in January, the American Heart Association proposed creation of a national registry of cardiorespiratory fitness data to establish norms and help physicians use them in treating diseases associated with obesity and sedentary lifestyle. A project to compile that information has been launched in a dozen health centers across the country, and the Heart Association hopes to expand it.

“Although [cardiorespiratory fitness] is recognized as an important marker of both functional ability and cardiovascular health, it is currently the only major risk factor that is not routinely and regularly assessed in either the general or specialized clinical setting,” the Heart Association wrote in its policy statement in the journal Circulation.

Still, there are caveats. Normal heart rates can vary by as much as 20 beats per minute, and sometimes people grow overly concerned when their statistics don’t mirror the norm.

“ ‘Normal’ has great variability — even maximal heart rate can be as much as +/- 20 bpm from prediction equations,” Benjamin D. Levine, a professor of medicine, cardiology and exercise science at the University of Texas Southwestern Medical Center in Dallas, wrote in an e-mail. “The problem is when people deviate from ‘norms,’ they get worried.”

Some fitness activities defy efforts to define what is normal. Experts agree that strength training is essential to ward off the roughly 1 percent annual loss of muscle mass that occurs after age 50 and that flexibility and balance exercises are nearly as important. But it’s not easy to offer advice that is applicable to a widespread population.

“It is difficult to set age-related norms for muscle strength because there are so many variables,” said Rosemary Lindle of Professional Fitness Consultants in Bowie. Those include genetics and body size. Some people may have strong upper bodies but weaker lower bodies.

“What a 55-year-old should be able to do in terms of pushing a weight . . . is going to depend on so many other factors,” Myers said, “whereas anyone can get on a treadmill” and take roughly the same exam.

And some tests may not be right for everyone, especially the elderly. “Not all these tests would be appropriate for every single individual,” said Jacque Ratliff, an exercise physiologist for the American Council on Exercise. “Not everybody is going to be able to run 1.5 miles.”

The American College of Sports Medicine offers modified fitness tests for older people, including a sit-and-reach flexibility check that is done on a chair rather than on the floor, according to Barbara Bushman, a professor in the kinesiology department at Missouri State University.

The takeaway, experts said, is to measure yourself against norms where appropriate, consult trainers or other professionals to help gauge your progress, but keep up a regular exercise program at all costs, especially as you grow older.

“Exercise is the best medicine there is,” Cooper said. “It has an effect on everything in a positive way.”