The 5BX plan of exercises, developed by The Royal Canadian Air Force has always struck me as a very scientific way of keeping fit, in the confined spaces of modern urban housing, not to mentions small rooms one gets cooped up in while travelling. Absolutely no equipment is required and all parts of the body are worked out.
I heartily recommend the programme to everyone who cares to listen. (It is another matter that I am able to stick to the exercise program pretty sketchily and skipping the hard parts! I am a rather generous person when it comes to putting myself through pain-producing exercise regimen and excuse myself readilly every now and then. It has something to do with the fact that my weight fluctuates around the 66 kg mark, with a tolerance of 1 kg and I consider myself a successful weight-watcher.)