You may use your fitness tracker mostly to count steps, but don’t ignore your heart-rate metrics—they can tell you a lot about your health. Devices now deliver a variety of heart-rate measurements, including resting rate, walking rate and variability (the variation of time between beats). Some can be programmed to notify you of a possible problem, such as a heart rate that is unusually high, low or irregular. Without getting fancy, however, your basic heart rate alone can be revealing.

The details

The heart rate is usually measured as the number of beats per minute (bpm). In adults, a healthy resting heart rate can range from 60 to 100 bpm. “It is highly variable. There’s no so-called normal,” says Dr. Michael Snyder, professor of genetics at Stanford University’s School of Medicine. For athletes and the very fit, it can be as low as 40 bpm, according to the American Heart Association. Heart rates generally increase while one is walking, running, or conducting a Zoom meeting. Alcohol and altitude increase the heart rate, as does stress.

The ability to monitor heart rates continuously, rather than once or twice a year in a doctor’s office, is relatively new, and physicians warn that the devices aren’t always accurate. The makers often don’t disclose the algorithms they’ve used or how they’ve tested the data the devices deliver, cardiologists and researchers say.

However, some doctors say it may be worth noting if there is a significant difference in your on-vacation heart rate and your at-work heart rate. “From an evolutionary standpoint, there’s definitely a correlation between how long you live and a lower heart rate,” says Dr. Yas Moayedi, a cardiologist and clinical associate at the University Health Network in Toronto, Canada. Being in a stressful environment for a prolonged time certainly can have consequences, she says.

Even if not precise, directional heart-rate patterns can be revealing. Dr. Moayedi experienced that first-hand when her own heart rate went up to 120 bpm on a day she was to give a speech. It wasn’t the unusually high rate that worried her most, it was the consistency of the high reading. Normally, heart rate fluctuates throughout the day, influenced by the physical, mental and behavioral changes that follow a 24-hour cycle. She was pregnant, and it turned out she’d become so severely iron-deficient that she needed an infusion. “My heart was compensating by beating really fast so it could meet my body’s demands,” she says.

“When you’re ill, your heart rate almost always changes,” says Dr. Snyder. “We think it’s better than taking your temperature, particularly for coronavirus.” In a study published in Nature in November, he and other researchers found that 26 of 32 study subjects infected with Covid-19 had elevated heart rates as many as nine days before symptoms; in most, the increases were extreme. Dr. Snyder’s own elevated heart rate alerted him to his Lyme Disease.

Can your heart-rate metrics help you get fit? All types of sports reduced the resting heart rate in healthy people and endurance training and yoga reduced it significantly in both men and women, according to a review of 191 studies published in December 2018 in the Journal of Clinical Medicine. How much exercise it takes to lower the heart rate depends on the person, Dr. Snyder says. “A lot of people say get 20 minutes of a good workout every day, but this exercise business is not all worked out.”

Dr. Harlan Krumholz, a cardiologist and professor of medicine at Yale University, says fitness trackers can be helpful in evaluating patients with heart palpitations or rapid heart rates but haven’t been studied enough to make individualized recommendations.

“I don’t say ‘track your heart rate and try to get it down ten points,” he says. Instead, his advice is generally to get moving: “More activity is better than less activity.”

Write to Betsy Morris at betsy.morris@wsj.com