But after a physiologist revamped his once-leisurely training, adding some strenuous pedaling, Mr. Marchand decisively bettered his own records and, at the age of 103, set a new world mark for the most miles pedaled in an hour by a centenarian.

His efforts help to belie a number of entrenched beliefs about older people, including that physical performance and aerobic capacity inevitably decline with age and that intense exercise is inadvisable, if not impossible, for the elderly.

Other studies this year reinforced the notion that age need not be a deterrent to hard exercise and that such workouts could be key to healthy aging. An animal study that I wrote about in July, for instance, found that frail, elderly mice were capable of completing brief spurts of high-intensity running on little treadmills, if the treadmill’s pace were adjusted to each mouse’s individual fitness level.

After four months of this kind of training, the exercised animals were stronger and more aerobically fit than other mice of the same age, and few remained physically frail. Perhaps most striking, “the animals had tolerated the high-intensity interval training well,” one of the scientists who conducted the study told me.

But of course, mice are not people. So it was another study this year that to my mind provided the most persuasive evidence that strenuous exercise alters how we age. In that study, which I wrote about in March (which became my most popular column this year), scientists at the Mayo Clinic compared differences in gene expression inside muscle cells after younger and older people had completed various types of workouts.