If you wanted to spend two weeks cycling through Denmark, you've just missed a good chance. A research team at the University of Copenhagen arranged just a 2700km cycling trip, to study how older people respond to exercise. The scientists measured the metabolism of the bikers and found a problem, although not necessarily the problem most people would have anticipated.
Their definition of "older people" involved a lot of wiggle room. The group doing the trip included 71-year-olds, but also included people as young as 46 -- which only counts as "senior" if you're at a Justin Bieber concert or trying to found a start-up. However widespread the sample of ages, the group did find something interesting: The test group had a problem increasing how much they ate as they exercised more.
We all have a basal metabolism -- the rate at which we expend energy when we're just sitting around. During the trip, the older biker's metabolisms went up to four times their basal metabolism. This is a good sign. It puts them only slightly behind Tour de France cyclists, who expend up to 4.3 times their basal metabolism.
Tour de France cyclists are able to up their food intake to catch up with the energy they're expending. These bikers didn't. They were hungry -- or as the study puts it, they had "increased motivation to eat" -- but they couldn't put away enough food to compensate for the rate at which they were burning energy. It was only a two-week study, and it's possible that, given time to adjust, the older bikers could start eating more or biking less. If there's a real barrier to eating enough food as we age, that presents a problem for people who want to be very active when they're older.