Their answers revealed that, although the men remained physically active, none were competitive athletes at this point. In general, they exercised for a few hours each week by walking, jogging or cycling.

But their fitness remained relatively outsized, she found. Each man’s VO2 max had declined significantly since 1968, when he was in his 20s and competing, and also since the second testing in 1993. But their 2013 VO2 max numbers still placed them in the top 10 percent or so of older American men, based on tables developed in recent years using cardiovascular testing data from thousands of aging people.

These findings might indicate that the former athletes were genetically gifted, Dr. Everman says. They might be physiological outliers whose lucky cardiovascular quirks lingered into old age and allowed them to remain unusually fit in comparison to other older people.

But she is skeptical of that reading. Numerically, the men’s VO2 max levels declined more during the 45 years of the study, she says, in terms of the percentage of the capacity they lost per decade, than would be considered normal, based on data from nonathletes.

But they were declining from such a height of fitness that, even as their capacities contracted, the men’s fitness stayed above average, she says.

Such data suggest that squirreling away fitness when we are young with sustained, frequent exercise might help to blunt some of the losses later, she says.

But the broader message of the study, she says, could be that we may need to rethink what normal fitness is or should be in older people. The tables that doctors and other experts currently use to determine “normal” fitness have been constructed with data gathered from typical older people today, many of whom have been sedentary for years.