U.S. Olympian Kim Conley has managed to maintain an unusual running streak largely through relentless effort: She's in her 16th straight year of beating her personal record in the variety of distances she competed at, from 1,500 meters to 10,000 meters.

"I didn't start out as fast as some of the other runners. But I have a constant desire to continually improve myself," said Ms. Conley, who lives in Sacramento, Calif., and is an assistant track coach at University of California, Davis.

The 28-year-old began her college running career at UC-Davis, where she majored in exercise biology, with a 17:27 time in the 5,000 meters and graduated with a 16:23 personal record. She competes at other distances, including the 3,000 meters. This winter she handily outran the field in the 3K at the ultra-competitive Millrose Games, an annual indoor track-and-field event in New York.

Ms. Conley burst onto the international track-and-field scene at the U.S. Olympic trials in 2012. In the last heat, she went from fifth place to third in the final 200 meters and earned a 5,000 meters spot on the U.S. Olympic team. She qualified for the London Olympics with a time that was just under 15:20.

She didn't qualify for the finals in London, but she still shaved her 5K time to 15:14. Ms. Conley is hoping to qualify for the 2016 Olympics in Rio by running the 5,000 meters in close to 15 minutes.