Research suggests that many fitness-themed Instagram accounts risk doing more harm than good. Here’s how to find #fitspiration you can trust.

In a new study, researchers found that nearly two-thirds of the 100 most popular “fitfluencers” — a term that can describe any influencer who posts content related to fitness — lacked sound advice or posted messages that could negatively affect people’s mental and physical health by, say, promoting exercise as a tool to become skinnier.

“Much of what could be called ‘fitfluencer’ content is really just ‘thin-spiration’ in disguise,” said Renee Engeln, a professor of psychology at Northwestern University who studies how media influences body image and was not involved in the research.

Several previous studies have shown that exposure to images that encourage a specific physique is correlated with a dip in body satisfaction, mood and self-perceived sexual attractiveness. It has also been linked to disordered eating.

Being able to distinguish between health-promoting accounts and potentially harmful ones can be challenging, even for researchers, Dr. Engeln said.

“An influencer might post a useful tutorial on how to safely do squats,” she wrote in an email, “but then follow it up with content promoting ineffective (or even dangerous) weight loss supplements.”

So how can you find credible accounts? What should you look for when deciding which fitfluencers to follow? Here are four rules of thumb from experts.

Stephanie Roth-Goldberg, a clinical social worker and therapist in New York who works with athletes, suggested asking yourself: Does this fitness influencer make you feel good in your own skin?
If browsing the account leads you to feel guilt or body shame, she said, that should be an automatic unfollow, as research has shown that these feelings can fuel unhealthy fitness habits and undermine both the physical and psychological benefits of exercise.

If you’re a parent of teenagers with social media accounts, it’s important to guide them through the same process, according to newly issued recommendations from the American Psychological Association.
The group urges parents to train kids to question the accuracy of social media content — before they even open accounts — and to discourage them from comparing their bodies to what they see online.
“One of the best things parents can do is sit with their kids and open up a conversation”  about social media, Ms. Roth-Goldberg said. Not only can this help parents understand what their kids are getting out of each account, it can also provide kids with language to describe how what they see makes them feel.

 Find accounts that focus on what your body can do. Take a close look at the images, videos and text featured on an account. When we are exposed to content that encourage us to exercise for functionality, strength and mental health, we are more likely to cultivate a healthy relationship with our bodies.

Make a point to follow accounts that focus on finding joy and confidence in movement itself, but be wary of fitfluencers who share before-and-after photos that highlight fat loss, or images, like glistening abs or disembodied legs, that treat body parts like objects that need to be perfected.

 Kelly K. Roberts, a running coach and body-positive fitness influencer based in New York City who has nearly 70,000 followers on Instagram, initially built a following by posting images that charted how her physical appearance changed through running. But when she discovered that her own social media habits were causing her to fixate on her weight, she switched to posting about running for the fun of running.

 “Any time you post about your body, you’re giving people an opportunity to self-compare and self-objectify,” she said. “You’ll rarely see me talking about my body anymore. I just exist in it.”

 To find accounts that focus on movement, search hashtags like #joyfulmovement, #intuitivemovement, #inclusivefitness and #bodypositivefitness. Seek out fitfluencers with official credentials. You’re best off following professionals who have formally trained in the field you are interested in, said Cedric Bryant, the president and chief science officer of the American Council on Exercise. “You can’t rely on the number of likes that a person has or number of followers as being an indicator of the quality of their advice,” he said. Instead, look for references to their credentials and experience, whether it’s a master’s degree or a coaching certificate. Be wary of fitfluencers who offer advice outside their expertise, Dr. Bryant said, particularly regarding diet and nutrition.

“Even if a person has fitness credentials, if they don’t also have proper training in nutrition, I would tread carefully,” he said. “Make sure they’re staying in their lane.” Look for influencers who feature a range of body types, ages and abilities. Fitness looks different for everyone, despite long-held cultural misconceptions about exercise and body shape and size. “Seeing a range of body types engaging in fitness activities is a key step in moving away from the stereotype that fitness is just for young, thin, completely able-bodied people,” Dr. Engeln said. The more our fitness feeds feature a diversity of bodies, the more we can expand our ideas about what we ourselves are capable of, she said, and “feel more comfortable trying new things.”

 Danielle Friedman is a journalist in New York City and author of “Let’s Get Physical: How Women Discovered Exercise and Reshaped the World.”