Over one third of the entrants (162/395) in this weekend’s Olympic Marathon Trials in Los Angeles are at least 30 years old. Thirteen are over 40, including two of its top contenders. So in theory, the six <a href=/articles/2014/10/shalane-flanagan>marathoners</a> who make it onto Team U.S.A. could potentially be some of the oldest athletes in Rio. Yet anyone who has ever <a href=/articles/2013/07/marathon-strength-training>trained for a 26.2-mile race</a> knows that the demands of the sport are pretty punishing. Which makes us wonder, how is it possible for runners to thrive for so long in such a challenging, high-impact sport?Case in point: Meb Keflezighi. In 2012, at age 37, he became the oldest man to win the Olympic Marathon Trials. Now 40, Meb will be back again this year, attempting to qualify for his fourth trip to the Olympic Games. But it’s not like he just barely made it onto the roster: Meb’s 2:08:37 qualifying time (from his 2014 Boston Marathon win) is the fastest one on Saturday’s line-up.“From a motor learning perspective, the more time we practice an activity like running, the more potential we have to get better and be more consistent. Also, although somewhat controversial, if a person continues to run throughout their lives, there is research that suggests you increase the volume of Type II slow-twitch (aerobic) muscle fibers as compared to the Type I (fast-twitch) fibers. These slow-twitch fibers are key to effective performances in endurance sports. So theoretically, over time, you’d see improvements,” says Justus Ortega, Ph.D., a kinesiology professor and director of the Biomechanics Lab at Humboldt State University in Arcata, CA.Three-time Olympian Deena Kastor, 42, has not only won a bronze medal in the event (2004, Athens), but she also holds the American Record in both the marathon (2:19:36) and half-marathon (1:07:34). A 2:27:47 finish at the 2014 Chicago Marathon earned her a spot on the starting line this weekend.“I believe consistency is the key to gaining strength,” she says. “When you build your musculature and your cardiovascular systems by running over the years, your body grows in so many unquantifiable ways, creating new capillaries, releasing endorphins and creating a foundation of joy.”Kastor notes that there is more balance in her life and training these days, too. “I’m not sure if I need more <a href=/articles/2015/11/post-marathon>time to recover</a> now, because I’m not running as many miles as when I was younger. I used to narrowly focus on running, but now I have a lot more responsibilities in the day,” says the mom/wife/writer/president of the ASICS Mammoth Track Club/executive producer of Boston, the film. “I simply love my time running because, well, it’s simple. It always gives me whatever I need, whether that’s time to create a to-do list, reflect on my writing or intensely focus on my running goals.”Elites aren’t the only ones enjoying distance running as they get older, either. One recent study showed that the overall participation among master runners (over 40 years old) in the New York City Marathon had increased three-fold for men and seven-fold for women over the last 30 years. And the <a href=http://extremephysiolmed.biomedcentral.com/articles/10.1186/2046-7648-2-21 target=_blank>fastest ultra-marathon times</a> continue to be clocked by runners who are between 30 and 50 years old.It’s important for anyone who wants to keep logging more and more miles to learn how to strike that balance of putting just enough—but not too much—stress on your body, says Ortega. “Too much stress, and the body breaks down (over sore muscles, inflamed/strained tendons and ligaments and/or stress fractures). However, with an appropriate amount of stress from activities like running and biking, our bodies actually respond by growing stronger.”

Why marathoners get better with age

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