On April 19, 1967, Kathrine Switzer — registered as K. Switzer — found herself about to be thrown out what was then the all-male Boston Marathon before a husky companion, Thomas Miller of Syracuse, threw a block that tossed a race official out of the running instead. (Associated Press)

Thousands of runners will fill the streets of Washington on Sunday morning for the 45th annual Cherry Blossom Ten Mile Run, likely unaware of how one woman running among them has impacted so many of their lives.

More women are expected to participate in Sunday’s race than men, but when Kathrine Switzer, the first woman to formally enter and complete the Boston Marathon in 1967, won the women’s division of the inaugural Cherry Blossom race in 1973, she was one of only 12 female finishers.

Comparatively, more than 60 percent of the 16,279 finishers in last year’s race were women, and according to data collected by not-for-profit organization Running USA, female finishers annually have outnumbered males at all U.S. running events combined since 2010.

Switzer, 70, has been at the forefront of this revolution.

“It’s incredible it’s happened so quickly,” Switzer said earlier this week from her home in New York’s Hudson Valley. “I always knew women’s running would be popular and publicizable, and I said it’s as popular and publicizable as men’s, but I had no idea it would become almost a women’s sport now. Women are driving the sport, and it’s because of the empowerment and self esteem from running.”

Kathrine Switzer training in Wellington, New Zealand in March 2017 in preparation for the Cherry Blossom Ten Miler. (Courtesy of Hagen Hopkins)

In a few weeks, Switzer will celebrate the 50th anniversary of her life-defining moment at the Boston Marathon by running the race for the first time since 1976. Sunday in the District will be part training run and part meet-and-greet for Switzer, who still runs regularly while splitting time between New York and New Zealand. To prepare for Boston, she has averaged 35 to 40 miles a week.

Switzer’s desire to use the sport as a force for social change began shortly after Boston Marathon co-director Jock Semple attempted to physically remove from her from the 1967 race.

National newspapers printed the photographs showing Semple lunging at Switzer’s bib number a few miles into the race, which immediately brought public attention to the plights of female runners during a time when women were thought to be too fragile for long-distance running.

“When I think of Kathrine Switzer, I just think of somebody that’s a daredevil but also a trendsetter and a pioneer for what my life has become,” said 2004 Olympian Carrie Tollefson, who will run the Cherry Blossom race for the first time Sunday. “I owe a lot to her and other women of her era who didn’t exactly have the opportunities that I have.”

In 1984, Switzer successfully campaigned for the women’s marathon to become an Olympic sport, a pivotal moment that helped pave the way for professional female runners like Tollefson. More recently, Switzer started a nonprofit, 261 Fearless, that aims to empower women around the world through running.

And her story continues to resonate. Switzer still receives tear-stained letters of gratitude, and her bib number from the 1967 Boston Marathon — 261 — has reached mythical status for some runners who wear it on their arms as inspiration or, in some cases, honor it in the form of a tattoo.

“It obviously meant so much to them to have this sense of fearlessness,” Switzer said of what her bib number represents. “They’ve really inspired me that way.”

Kathrine Switzer running at the Cherry Blossom race in 1997, where she placed 17th out of 102 women in the 50-54 age group. (Courtesy of George Banker)

When Switzer attended high school at Madison and then Marshall in Northern Virginia — a place she said “will always be home” — opportunities for young female athletes were limited in the pre-Title IX era.

The only girls’ teams available at Marshall were field hockey, basketball, softball and tennis, and Switzer initially wanted to become a cheerleader until her father encouraged her to shine on the playing field instead, an exchange that remains one of the most impactful moments of Switzer’s life.

“All you need to do is to give kids the opportunity. . . . Positive reinforcement is everything,” said Switzer, who ended up playing field hockey and basketball in high school. “I don’t start any speech without telling that story of my dad saying, ‘Cheerleaders cheer for other people. You should have people cheer for you. Life is to participate, not to spectate.’ It was critical.”

Switzer registered for the 1967 Boston Marathon under the name “K.V. Switzer” not with the intention of becoming a radical women’s pioneer in the sport but to prove to her coach, Syracuse’s Arnie Briggs, that yes, women can run 26.2 miles.

The then-20-year-old finished the race in 4:20:02, but Semple later disqualified her for a list of reasons, including running with men. She said the hate mail started to pour in, and acceptance of Switzer at races was gradual. But Switzer had little doubt that what once seemed extreme would become the norm.

“I’m a long-term gratifier,” she said. “I’m willing to wait it out. I’m willing to take it step by step.”

When Switzer ran the Cherry Blossom race again in 1997, she placed 490th out of 2,149 female finishers. She also spent time as an elite runner, winning the women’s title at the 1974 New York City Marathon and running a personal best 2:51:37 at the 1975 Boston Marathon before turning her focus to a sports broadcasting career. In more ways than one, Switzer has not stopped participating in the world she helped change.

She says her global foundation “is probably going to be biggest thing I’ve ever done,” and believes that if she had the opportunity, she would have been an elite ultrarunner. When talking about her post-Boston goals, Switzer lowered her voice and spoke with a passion of someone who is always looking ahead.

“One of the races that’s always been on my bucket list has been the [56-mile] Comrades Marathon in South Africa,” she said. “I’ve wanted to run that ever since I first heard about it in the late ’60s, so who knows, I might get there yet.”

45th annual Cherry Blossom Ten Mile Run

More than 16,000 runners from all 50 states and 14 countries will convene Sunday to run one of the marquee 10-mile road races in the nation’s capital. The scenic route takes runners around the tidal basin near the cherry blossom trees, across the Memorial Bridge and around the East Potomac Park. There will also be a 5K run/walk and a 1K kids’ run. The elite women will start at 7:18 a.m., followed by the elite men and first wave at 7:30 a.m.

Best viewing locations: Along Independence Drive and on the west side of the Lincoln Memorial as runners run over and back the Memorial Bridge

Defending champions: Men’s — Sam Chelanga (48:26); Women’s — Veronicah N. Wanjiru (53:12)

Website: Race results will be posted at www.cherryblossom.org