From version 4.0 onwards, MyMotion and MyMotionFree use Apple Healthkit (when available) to read the users weight and write data related to workout statistics to the Apple Health app. The user must give explicit permission for this.
MyMotion and MyMotionFree collect data from your device for the purposes of providing the user with workout statistics and showing progress on a map. The data is only stored locally on the device unless the user explicitely chooses to share via iTunes, iCloud, email etc.