Fonty
I don't work now xander but have done so in the past. A personal care job with long hours and heavy lifting as well as regular strenuous karate workouts. I still do the karate workouts today without any problem. I read somewhere, it may have been Shelton, that it was suspected that some at least of the exhaustion felt while fasting was psychosomatic. They found very often that those who believed they could work through a fast were able to do so. Many who planned to be resting however ended up bedridden during their fasts and barely able to get up a lot of the time. In these cases the very first taste of food would bring a return to incredible energy, long before the food sugars could have broken down and entered the bloodstream to be of any use.
I don't plan to take time out, I just allow more time for rest before and after working out. And if I have my kids I don't have any trouble keeping up with them as a rule either. I don't even need water for my karate workouts and have done hard sweaty sessions after 5 days or more without food or water.
I think at least part of the reason I stay active is that I send a message to my body each morning with my Early Morning Stretch that I need to be active. It's not strenuous in itself but it loosens all the joints and stretches all the major muscles in preparation for the day. I swear by it, it should be part of everyone's daily health regime.
Andrew.