Maybe this is how we'll work out in the future: throw on a pair of shorts, strap on our virtual reality goggles, and hit the weights.
Researchers from the University of Wisconsin-Madison are doing something like that (although, of course, the weights don't weigh anything) by creating a virtual reality simulator called the Cave Automatic Virtual Environment, or just CAVE, that works by tracking your muscle movements. Users put on a pair of goggles and strap electromyography (EMG) equipment onto their arms, step into a room that projects images of objects, and interact with faux-3-D stuff. Specifically, in the video here, the researchers are having the users pick up a weightless weight.
By using the EMG to track how users pick up a real weight, the researchers can determine the movements necessary to pick up a weight in the invented environment. Grab hold, stiffen your arm, and lift. It doesn't sound like much of a workout, but the researchers say it could be useful in therapy for people recovering from a stroke or other illness.