I believe that as long as the physical ideal includes a certain level of musculature (or lack of body fat), there will be motivation to continue to exercise and try to develop one’s body. But I would agree with the judgment implicit in your question that driving a mile to the gym and running on a treadmill for 2 hours is ludicrous. If we want to get into sci-fi forecasting, though, I don’t think that the future you described would be at all sustainable. I believe that we will not be able to produce levels of energy sufficient to sustain our lazy lifestyles, and will be forced to bike places, generate our own power, and maybe even grow our own food.