Smartphone fitness applications aim to change people’s behaviors, but often without the most effective tools, a new study shows.

“Behavior change techniques are the tools that have emerged out of decades-old research on behavior change which have shown some level of effectiveness at helping people to modify their behavior,” said David Conroy, the study’s lead researcher from Northwestern University in Chicago.

The "app space" is "exploding,” Conroy said in a phone call. “There are new apps coming out every week, even every day, and I think it would be really hard to tell which one you want to use if you were a consumer.”

More than half of American adults own smartphones - and half of those owners use some type of fitness app, Conroy and colleagues wrote in the American Journal of Preventive Medicine.

But, Conroy said, for the vast majority of these apps, there is no research on their effectiveness. One way to start that evaluation would be to look at what types of behavior-changing techniques the apps use.

In November 2013, Conroy and colleagues identified the 100 top-selling health and fitness apps in the Apple iTunes and Google Play marketplaces. Half were free; the other half were available for a fee.

The researchers looked for any of 93 possible behavior-changing techniques in the apps, including social support, instructions, demonstration, feedback, goal settings, prompt and self-monitoring of behavior.

Altogether, the apps used 39 behavior change techniques. Each app had from one to 21 techniques, with an average around seven per app.

The study team discovered that apps generally fell into two categories. About 48 percent focused on support and feedback through social support, approval from others and feedback on behavior. The other 52 percent offered support and education through social support, approval from others, demonstrations and instructions.

“It seems like almost all of the apps now are trying to find ways to help connect with Facebook, Twitter and Instagram,” Conroy said. “They want people to have a social connection.”

The study shows that social media integration is pervasive, Conroy said, even though there is only limited research showing social media can positively affect behavior.

The researchers only looked at what techniques were include with each app, they did not test whether or not any of the apps were effective in helping people become or stay more physically active.

Sherry Pagoto, a psychologist at the University of Massachusetts Medical School in Worcester, said in a phone interview that the range of behavior change strategies being used in health-related mobile apps is narrow compared to what’s used in clinical practice.

“So I think (there's) just so much more room to grow when it comes to these health apps,” said Pagoto, who wasn’t involved with the new study. “They don't really seem to reflect the behavioral sciences and what we know about behavior change.”

Pagoto said the good news is there are some evidence-based strategies in some of these apps, but app developers could do more.

Conroy said that while some apps have more behavior change techniques than others, none of them are silver bullets. They shouldn’t replace the guidance of fitness and health professionals.

“A lot of these apps, it turns out, are kind of hollow,” he said, adding they look nice and have many features, but no techniques to motivate people who aren’t currently active.