How Often Should I Train At A Sport, Martial Art, Or Exercise?

This is a tricky one, because there are several theories and many different ways that are borne out in practise.  Let's imagine a bench line at three times per week.  If you can practise a minimum of three times per week, you will make significant strides towards your goals.  More than that can be over tiring or actually have less effectiveness. Developing good physical and mental habits takes time and three times per week increases your ability to get those habits locked into you.

However, if you want to work out, then you can work out about five or six times, as long as your exercises change on a daily basis so not to over stress any part of your body too much.

You should have at least one day to rest regardless, consider it the time when your body and mind seem to relax, but end up doing most of the hard work of changing.