We manage separate sessions on different devices. An individual can use Trayn from as many devices as they want.

We only have a problem (very theoretical), if the user wants to use different languages on every device, because we save that information and the last setting will be used. 

That means, if the athlete uses the app at school in English, he sees everything as he should. If his mom logs from the iPad at home, but sets the language to Spanish, the experience for her son might be a bit confusing: the app will be in English, but, if Spanish content is available (e.g. for some exercises), the Spanish translation will be used.