All of the above plus muscle atrophy that makes stuff like IT band issues feel like knee pain. I'm in phenomenal shape for a 40+ year old and I have to spend a significant amount of gym time doing yoga and correctional lifting instead of body building style lifting.
I actually started working on the next revision that will have 4 USB-A ports in a panel via extension cables so the pi used is irrelevant AND it will look much more slick.
I wanted to leave it open so it's more universal in what can be fitted in there but I may make a revision in the future that is more model specific if I end up printing another one for a 5.