“So, Samson, how many days per week should I practice?”  -That’s a good question.
If you don’t practice enough, you won’t be improving to your full potential.  If you practice too much, you will likely get burned out or injured.  At one point, China went to a longer workweek without giving days off … and they weren’t productive.  In one particular country, at a national table tennis training center, the coach decided to do 28 days of practice, and then two days’ rest.  The players were getting injured and didn’t have sufficient rest.  I think that we see the best balance to this question in the Bible, Genesis 1:31-2:3 And God saw everything that he had made, and behold, it was very good.  And there was evening and there was morning, the sixth day.  Thus the heaven and the earth were finished, and all the host of them.  And on the seventh day God finished his work that he had done, and he rested on the seventh day from all his work that he had done.  So God blessed the seventh day and made it holy, because on it God rested from all his work that he had done in creation.
I think this is the perfect balance for table tennis and for life – six days of hard work and one day of rest.  God made us.  God designed us.  God knows our bodies more than we could ever possibly know.