If I get the chance, which doesn't always happen, I like to do a few minutes of gentle stretching (qi gong or yoga) before meditating. It improves circulation, as I think Guy said, and flexibility so I'm able to sit more comfortably. It also provides a cut-out from my other activities, helping my mind to settle more quickly when I do sit down.
As for 'workout', working up a sweat for the sake of fitness ... I'm sorry, that must be something other people do.
I play a bit of sport and like the fact that it helps me stay fit, but I find exercise for the sake of exercise so excruciatingly tedious I just can't bring myself to do it.