An 80-year-old woman has an elite VO2 max. She's as healthy as a 60-year-old thanks to a simple routine.

Linda Kelly built elite fitness over the years by staying consistent. Nathaniel Wilder for BI "I have always seen myself as a very ordinary person with no real athletic ability," said Linda Kelly. Still, at 80, she has completed multiple half-marathons and routinely hikes, bikes, and runs around her part-time home in Anchorage, Alaska. Kelly is as fit as someone decades earlier, with the lab results to prove it. Her son, cardiologist Dr. Jake Kelly, put Kelly to the test on a treadmill and f...