An Olympic medalist was 'prepared to implode' before running the Chicago and Boston marathons on back-to-back days

• Shalane Flanagan is attempting to run the world's six major marathons in 43 days.
• The Olympic medalist wants a sub-3-hour finish in each and did in the first four so far

Shalane Flanagan was "prepared to implode" while gearing up for her second marathon in as many days.

But midway through running the 125th Boston Marathon on Monday - just hours after completing the Chicago Marathon more than 800 miles away - the Marblehead, Massachusetts, native had a stunning realization.

"I looked over at my incredible running buddy [Andrew Bumbalough] and said 'I think I feel better than I did yesterday,'" she wrote on Instagram after the race. "'I think I'm having a good day.'"

She was right, and it showed in her results. In her hometown marathon, Flanagan bested her Chicago time by a full six minutes despite carrying the fatigue of having run an entire 26.2 miles the day before. Now, she's just two marathons away from achieving her highly ambitious goal: running each of the world's six major marathons in under three hours - all in 43 days.

"My body is going to let me do something that's never been done before," Flanagan wrote on Instagram. "And it feels so good to have that realization at home."

"6 marathons, in under 3 hours, feels so close I can taste it," she added.

Flanagan - who won the 2017 NYC Marathon nine years after earning a silver medal in the 10,000 meters at the Beijing Olympics - retired from professional running in 2019. But after having "fallen back in love" with running, as she wrote in an Instagram post this September, Flanagan decided to step back into the spotlight for a feat of epic proportions.

The condensed marathon schedule this fall - Berlin, London, Chicago, Boston, Tokyo, and New York City in six weeks - presented a unique opportunity to check all of the world's major races off her bucket list in rapid succession.

"I was like, this is incredible! Someone should do all of them this fall!" Flanagan told POPSUGAR in September. "And I thought, 'Why wouldn't I?' It's always been a bucket list item for me to do all of them."

Still, there were doubts she could get it done. The now 40-year-old went under the knife for two significant knee surgeries shortly after announcing her retirement. As The New York Times noted earlier this month, "her patellas have hamstring tendons from cadavers."

Completing just one sub-three-hour marathon would be a feat for anyone, let alone a runner with reconstructed knees. Running six of them? Ambitious is an understatement.

"I had to kind of assess, can I do that?" she told POPSUGAR. "I'm retired, and I'm a coach, and a mom, and I've had two knee surgeries. So I just was like, I don't know if I'm capable of it, but I really want to have a goal again."

She's proven everyone - herself, naysayers, father time, and physics inclusive - wrong so far. Berlin, the first of her slate of six, took her just two hours 38 minutes. A week later, she shaved off three minutes to cross the finish line in London two hours and 35 minutes after she started.

She placed 34th in Chicago on Sunday with more than 10 minutes to spare on her three-hour goal, and finished Boston in 2 hours and 40 minutes. Though she's run the race five times in her career, Flanagan says Monday's edition was "my best Boston, by far."

"I have NEVER loved it more than I did this morning," Flanagan wrote on Instagram a few hours after crossing the finish line. "... Running down Boylston meant more today than it ever has before."

A virtual version of the Tokyo Marathon is next on her docket. Though the in-person race has been postponed due to Japan's continued battle against the COVID-19 pandemic, Flanagan is planning to complete 26.2 miles in Oregon this coming weekend as a substitute.

Flanagan will round out her tour in New York City. In 2017, she finished in 2:26:53 to become the first American woman to take first place in the race in 40 years. Though she's not aiming for the podium this time around, she's hoping to find similar success as she crosses the finish line in Central Park on November 7.