Hi! This project is right up our alley. We've created multiple apps using google maps' API and tracking the user for live updates to the server. We've been using react-native and ionic for quite some time now, and we should not face any problems building your app according to your specifications. There is no particularly hard part in creating the app, however what will need a lot of work will probably be, by my understanding, the refresh rate of checking on the user's location to ensure that they are still at the gym (finding the best rate as to not overwhelm the server, and testing it to make sure it works properly). Hope to hear from you soon!