Rice, who ran a world record in the marathon in the 75-79 age group last year, has an incredibly high V02 max.

“That would slowly morph into a walk-run,” says Johnson, “and then eventually continuous running.” Begin with short intervals ...

Many training plans recommend the run-walk method as an option for beginners — an on-ramp to continuous running. But for me, it has become the key to maintaining a running habit while navigating ...

It involves a continuous run in which periods of faster running are mixed with periods of easy- or moderate-paced running, rather than periods of complete rest, as with interval training.