Video gaming is traditionally a sedentary pursuit, but that's changing thanks to interfaces that turn a player's motions into onscreen actions.

Already, more than 1.5 million copies of Dance Dance Revolution, which challenges players to shimmy in sync with animated characters, have been sold; more than one million units of the EyeToy, a motion-tracking PlayStation camera that inserts players into games, have been sold through February.

This year, Nintendo will introduce a game console whose controller contains a motion-tracking chip; in order to, say, thrust a sword in the game world, a player simply waves the controller in the air. And a startup called GameRunner has invented the first custom treadmill that controls off-the-shelf, first-person computer games. As the player walks, sensors underneath the belt translate its motion into in-game running or walking.