Wow i just finished reading an article about the Wii and its actions,
apparently some guy ended up in hospital with swolen joints that had to be operated on.
When playing tennis and such energy from the body is sent up the arm and into the bat/club/raquet which then passes on energy to the ball which causes it to move through the air. when playing wii energy from the body is sent up the arm and into the wiimote, however there is no ball to transfer this kinetic energy to so the energy is rebounded back through the wiimote and down the arm where its released in the weakest parts of the arm (i.e. the spaces between joints) apparently this builds up a fluid in the joints and can cause swelling and pain.
man i guess the wiis not so good for exersize lol! however this aint gonna stop me playing it