A former personal trainer, Carol Nigut takes twice-weekly brisk walks, does strength training three times a week, keeps flexible with yoga and maintains an enviable body mass index. Nigut, who is 63, 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 resume, 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 at adultfitnesstest.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, in San Diego, 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.’ ”

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 a half, then take your heart rate afterward. To learn how, visit the American Heart Association’s website, aha.org.

Baby boomers recall the grueling, “Kennedy test” that required them to do as many situps as they could while wearing one-piece gym 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.

If you just want to know where you rank on the couch potato-Olympiad continuum, look to the federal Physical Activity Guidelines for Americans, at fitness.gov. Adults should spend at least 150 minutes a week doing aerobic activities, plus muscle and bone-strengthening activities like push-ups, 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.”

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

n Strength training is an important 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.