“We’ve got an app for that.”

For gym owners, this is no longer just a trendy catchphrase—in fact, they now can utter those words with confidence. A growing number of all-star programs are recognizing the popularity and usefulness of mobile apps by developing customized apps specifically for their gyms. And the timing is right: more than half of mobile subscribers now use apps instead of Web browsing on their smartphones, according to Internet marketing research company comScore.