Clayton Young, who finished second at the 2024 Olympic Trials with a time of 2:08:00, did something he normally wouldn’t while training for this year’s Boston Marathon: he ran doubles on Saturdays—a long run of 25 miles in the morning, followed by extra 4-6 miles in the evening. It was unique to this training block, as he was coming back from an ankle injury and felt what he called the “urgent mentality” to build his fitness.

Running doubles is common among elite runners, whose mileage peaks in the triple digits. But doubles aren’t limited to the pros; there are good reasons for you to incorporate them in your own training.

Runner in Chief Jeff Dengate loves doubles (or even triples). “When you fire up the engine twice a day, all sorts of cool, important stuff happens under the hood,” he says. When you lace up for the second time during a day, you are increasing mitochondria , he explains, which are found in your cells, turning fuel into energy for your hardworking muscles.…