A former personal trainer, Carol Nigut, 63, takes twice-weekly brisk walks, does strength training three times a week, keeps flexible with yoga and maintains an enviable body mass index.

Nigut doesn’t need to gauge her fitness level; she sees the results. “While friends are having joint replacements, I’m avoiding surgery,” said Nigut, of Oro Valley, Arizona. “I don’t need to take medications. And I’m able to try new ways to stay active. Bird-watching, dancing, whatever; I’ll try it.”

If training is not on your résumé, though, how do you know if you’re fit? Google “How many situps should a 30-year-old male do?” or “How long should it take for a 50-year-old female to run a mile?” and you get thousands of answers, mostly from random sources that have nothing to do with fitness.

Enter the gold standard, the Adult Fitness Test (www.presidentschallenge.org):

“Every trainer organization has its own assessment and we don’t advocate one over another,” said Joy Keller, of the IDEA Health and Fitness Association, which educates trainers through publications and conventions. “But we recommend using some assessment before you start a new exercise so you can track your progress. If you’re not assessin’, you’re guessin’.”

Your four goals

The Adult Fitness Test measures four key components — aerobic endurance, muscle strength, flexibility and BMI. They are intertwined, in a good way. Run farther for more endurance and your legs get stronger. Practice ballet to gain flexibility and your BMI improves. No need for trainer supervision; you can do this test at home.

To gauge your aerobic endurance, run or walk a half mile, mile or mile and one half, then take your heart rate afterward. (To learn how, visit the American Heart Association’s website, www.aha.org).

To calculate your flexibility, use the “sit-and-reach” test. Put a yardstick on a box, with the 15-inch mark even with the edge of the box. Sit on the floor with your feet against the box, with the yardstick pointing toward your groin. Your score is how far on the yardstick you can reach.

For a BMI calculator, go to www.presidentschallenge.org.

Caveat: Muscles weigh more than flab, so a super-fit person can have a higher BMI than someone who considers reaching for french fries his exercise. So it’s no wonder many exercise buffs ignore this part. “After having seven kids, I’ll never have the same measurements,” said Vanessa Quigley, 42, of Orem, Utah. Instead of worrying about her BMI, her yardstick is her energy level, which usually reads “high.”

Some trainers who have served in the military prefer the U.S. Army Physical Fitness Test (www.army-fitness.com).

Your kid vs. national model

The kids’ version of the Adult Fitness Test is the FitnessGram (www.pyfp.org):

Baby boomers recall FitnessGram’s predecessor, the grueling, “Kennedy test” that required them to do as many situps as they could while wearing one-piece uniforms that didn’t stretch. Officially called the President’s Challenge Physical Fitness Test, its nickname reflected President Kennedy’s pledge to make America’s youth fit. It did measure performance.

Thank the Dallas, Texas-based Cooper Institute for developing FitnessGram in 1982, even though it was 2012 before the Presidential Youth Fitness Program officially adopted it and “sunsetted” the Kennedy test.

If you think kids should get participation trophies and high schools should ditch class ranks, you will applaud FitnessGram’s comparisons to “the norm.” If running faster than the others on his track team is your child’s goal, recycle his FitnessGram and cheer him on.

Do this at home

If you just want to know where you rank on the couch potato-Olympiad continuum, look to the fed’s Physical Activity Guidelines for Americans (www.fitness.gov).

Kids should have at least an hour of physical activity a day, said the guidelines. It should be mostly aerobic, but include muscle- and bone-strengthening activities at least three times a week.

Adults should spend at least 150 minutes a week doing aerobic activities, plus muscle- and bone-strengthening activities like pushups, situps and weightlifting at least two days a week. If this sounds too lofty, do what you were going to do today anyway. Whether it’s walking the dog or weeding the garden, chances are it’s on the guidelines’ activity list. As long as it keeps you in motion, it “counts.”

Fitness tips

Whether you exercise to maintain or improve your fitness level, consider these tips from trainers and trainees in the trenches:

• Strength training is the component many ignore, but it helps protect us from injuries, said Matt Cubbler, a 44-year-old trainer from Collegeville, Pennsylvania. “It gives you denser bones, like an inside coat of arms,” he said.

• Mix up your routine so it doesn’t get boring. “I work every muscle group each week, but vary the machines,” Nigut said.

• Set realistic goals. “If you’re 50, your goal can’t be to look like an underwear model because your body has changed,” Cubbler said. “But you can learn to lift weights you couldn’t lift when you were younger.”

• When you reach a goal, reward yourself with something other than food. Think spa day or a fresh yoga mat.

• An assessment should consider your gender, said Carol Ewing Garber, spokeswoman for the American College of Sports Medicine. “Women have lesser arm strength, for example,” she said.

• “Camaraderie helps you stick with it,” said Quigley, who attends an exercise boot camp with a friend. “We have a friendly competition.”

• If you can’t afford the local gym, check out park district classes, which often cost less.

• “Parents, don’t feel guilty for setting aside exercise time for yourself,” said Garber. “Consider it an appointment you have to keep — with yourself.”