Could we use it for regular martial arts training? The DBZ article for the HTC mentions no non-emergency use, and a little thought leads us to conclude that, probably not: inside the HTC, time passes as normal, which means that you don’t save any time. All the HTC is doing is rearranging relative time between groups. If you step in, you still age a full year before stepping out, and you will now die a year early by the realtime calendar. So what’s the point?

Plenty of people would benefit from an opportunity to adjust their life's timeline a bit relative to the rest of the world. To stick with the training premise, you might take a year to recover from an injury and get back up to form in time for the Olympics.