You write with your hands. When you are doing that, it is your muscles which are doing the actual work. But each work is to be done by specialised muscles. You can demonstrate this by doing this experiment. Tie a pencil to your forefinger and with that you write something on a paper. Then tie it to your wrist and again write on the paper. Next tie it to your forearm and write. As you go on using bigger and bigger bones and joints to write, you will find the effort is becoming more and more difficult and becoming more inefficient.
Affect of Gravity on Blood Flow
As with everything else on earth, gravity affects our blood flow also. This can be seen easily by the following experiment. Lift one of your hands and hold it high above your head. The other hand, you hold straight down. Maintain this position for about 1 to 2 minutes. Then look at both your palms. You will find the held high palm to be pale, while the held down palm will be redder.