This post has been updated. 

If browsing the Apple App Store for a fitness app and going through the hundreds of choices is enough to make your brain explode, check out this study from the University of Florida.

Researchers rounded up 30 popular free fitness apps for the iPhone, dissected what they do, and compared this against American College of Sports Medicine guidelines for physical activity.

In scoring the apps, researchers looked at everything from warm-ups, cool-downs and stretching to safety and assigned them a score for three separate categories: aerobic exercise, strength/resistance and flexibility.

More than half the apps met some of the criteria for aerobic exercise, 90 percent for some strength/resistance, but many fell short in flexibility. In all, two-thirds did not meet any flexibility criteria, the researchers wrote in the Journal of Medical Internet Research.

The final result, when the scientists combined those three scores to come up with a total quality score: Only one app -- the Sworkit Lite Personal Workout Trainer -- met more than half the criteria from the guidelines.

"The issues with these apps place users at risk for injury because the apps fail to prepare them to take on the exercises, use proper techniques and address safety issues," said Francois Modave, lead author of the study and an associate professor in health outcomes and policy.

Modave said he hopes the study, which he says is the first to explore the extent to which fitness apps are adhering to the ACSM guidelines, "starts a conversation" about how to design apps in a better way.

Here's a ranking of the apps that were tested. The total possible score is 14.

Update: Johnson & Johnson said the study "does not appear to be a fair or accurate rating and assessment" of its Johnson & Johnson Official 7 Minute Workout. The company said the app is based on a workout described in a peer-reviewed publication in the ACSM Health and Fitness Journal and is consistent with ACSM's guidelines.

Richard Cotton, national director of certification for the American College of Sports Medicine, said in an e-mail that the organization applauds the study for intending to “raise the bar in technology for physical activity.”

He said the ACSM is “very clear “ that all three components of exercise – aerobic, strength and flexibility – are necessary to meet guidelines related with respect to a comprehensive exercise program. He clarified, however, that the organization does not expect every app to include all the components of fitness (i.e. aerobic, strength and flexibility exercises).

Even apps that only address one area provide “potential value for the user making an exercise technology decision based on their individual health and fitness needs,” he explained, citing the Johnson & Johnson workout as an example. He said that app was designed to improve the muscular strength and endurance component while also encouraging progression to meet the aerobic guidelines and is consistent with ACSM guidelines in this regard.

“We encourage everyone to look for the technology support most appropriate to their goals and needs, and for the industry overall to continue its impressive progress, stimulated by such things as this study,” Cotton said.

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