One day in the summer of 2000, Peter Walsh decided to take up marathon running. And being a fatherly sort, he allowed his two young daughters, Dana and Alice, to tag along on a training run. "He thought we were falling behind and kept stopping, but three miles into it we were still right with him," Dana recalled one day last week. Peter Walsh eventually completed the New York City Marathon, but he never succeeded in outpacing his twin daughters. Now both 16, Alice and Dana Walsh are two of the best high school runners in the city and have long since moved on from jogs with their father to speedy training runs on their own. "We do everything in unison," Alice said while seated alongside Dana in a room at Convent of the Sacred Heart on the Upper East Side, where the two are juniors. "We got really competitive. We did the same events, and once we started we realized we wanted to win, not just have fun. In 8th grade, we started training much harder. Running has become a part of us. It's one of my favorite things to do, even though I know a lot of people would think that's crazy." Sacred Heart is a small school, with only about 50 students in each grade, but the Walsh twins have helped its cross country and track and field teams achieve outsized accomplishments. Earlier this month, Dana finished second at the New York State Association of Independent Schools (NYSAIS) Cross Country Championships, with a time of 20 minutes, nine seconds over five kilometers (Alice was out with a knee injury). At the track and field championships last spring, Dana won the 800 and 1,500 meters, while Alice finished second in the 400 hurdles. And they teamed up to lead Sacred Heart to second place in the 4x400 relay. Dana also holds league records in the 400, 800 and 1,500, while Alice has her heart set on capturing the 400 hurdles mark this spring. And in perhaps her most impressive feat, Dana won the 1,500 and set a new meet record in April at the Mayor's Cup, a competition for both public and independent school students in New York City. Alice finished eighth in the 400 hurdles. For both of them, the path to excellence began with their father and took a big step forward during a two-mile race at the NYSAIS Championships in 7th grade. "I wasn't doing well," Dana said, "but then Alice was screaming from the sideline, 'You're going too slow.' And that's when I realized that in running you shouldn't be comfortable at any point in the race." The duo's teamwork has been similar ever since. They fit the common stereotype of identical twins, often finishing each other's sentences. But when it comes to competition, their skills are complementary. Though they tend not to run in the same events, they both vividly remember a 400-meter race four years ago that came down to the wire, with both diving headfirst across the line. "We used to be really competitive," Dana said. "Now, we just help each other out. I help her in training and try to push her to work harder." "And I help her calm down when I think she's going to pass out from being nervous," Alice added. "I always tell her that she's definitely going to win. She's always been better than me, and I used to be kind of jealous. But now I just use it to motivate myself to work harder. It's a good thing. We work together, push each other. Having someone train next to you only makes you better." Despite their cheerful, bubbly nature, the twins' shared intensity is obvious. In the fall, while their friends play soccer, they run hill repeats to get ready for the cross-country course in Van Cortlandt Park. For three straight summers, they have attended a weeklong running camp upstate. And when they ran into Kara Goucher, an Olympian and the third-place finisher in the New York City Marathon several weeks ago, during a training trip to Florida, they managed to stay alongside her for a lap. Dana, meanwhile, carries enormous expectations for herself. She considers 8th grade her only successful fall season, even though she won the NYSAIS title as a freshman and finished second this year. At Nike Nationals, an elite track competition for the best high school runners in the country, she won the freshman mile two seasons ago. Running the mile again last June, however, she fainted midway through the race. "It was about 95 degrees and so humid," Dana said. "I just saw black and went down. I had the 800 the next day, and everyone was telling me not to do it. But I said, 'I didn't fly to North Carolina not to race.' I got a personal record." "This is normal," Alice said with a shrug. "It becomes completely about your mentality. I love track and cross country because there are times when you're by yourself, and how well you do is entirely in your control." The Walsh twins had time for an interview last Friday because classes were canceled for parent-teacher meetings. But instead of spending the rest of the day relaxing, they promptly zipped up a pair of windbreakers and decided to go for a training run in Central Park, conveniently located about 50 feet from Sacred Heart's front door. "I think we're going to do five," Alice said. Five kilometers? In ice-cold weather and freezing wind? "File miles." And off they went.