Re: Role of Tension and Body Conditioning in Aikido
For a place to start you can have a closer look at the warm up exercises done in aikido. You can use them to train moving in a relaxed way, moving from your center, keeping in touch with the ground, connecting different body part to each other.
For a simple example of what I mean: you know the exercise where you bend forward and backward with your hands somewhere vaguely above your head? Try that one with your hands clasped behind your head and see how it feels. It should make it more difficult to move from the shoulders, and help you make the movement more with your center. Once you've got that, you can keep your hands, still clasped together, just above your head, and try to do the whole movement without letting them drift away, but still keeping your shoulders relaxed.