The giants of technology have made one thing abundantly clear this year: You’re out of shape and need their help to get fit! Microsoft, the newest would-be coach, just rolled out a wristband-and-app pairing that was built to work with iOS, Android and Windows Phone.

Microsoft execs say the company is getting into the wearable business as a first foray into a big problem: how to identify useful intelligence in heaps of personal data. Microsoft says it can take sensor information from wearables and interpret it in the cloud...