I like physical work, but only for one or two hours (because I'm already old and I don't want to hurt any of my body parts:)

I also like mental work.

Two thousand years ago, one of the Greek philosophers said "everything in moderation".

So, a bit of mental work and a bit of physical work is a good combination. 

My major has involved to much brain works and if I don't have physical motions I can't focus more...

''How do you rest when you get tired of mental work.''

I do sport, playing energetic music and dance (Hip hop, Arabic dance,...), gym, going outside, break and cooking, making tea, go to the party, talking, etc...in this way, my mind is more ready for doing rest of brain work...I created an sport group and made my friends to join me after some hours brain works..because they needed too and I wondered how they could  have brain works for many hours without motions ans sports...