A quote from Today's Times
"Why do some feel the need to exercise more than others? It may be all in the Brain according to a study in Behavioural Neuroscience. Experiments with mice showed that those who ran the most had greater activity in the areas of the brain involved in craving food, drugs or sex when denied access to running wheels."
So what do you do when unable to train? Well I guess the boffins didn't offer the mice a keyboard and access to the RW Forum? :-)