Runners love numbers. Whether it's pace, finishing times or resting heart rate, we view figures as a sign of our progress, accomplishments and dedication to the sport. So it's no surprise that many of us struggle with one number that increases each year, regardless of how hard we train: our age.
But thanks to all the health benefits that running brings, you don't need to sweat each time a candle is added to your cake. "There's a big difference between biological age, or how old your body thinks you are, and chronological age - how old the calendar says you are," says Steven Hawkins, professor of exercise science at California Lutheran University in the US. "The biological ages of runners are at least 10 years younger than their chronological ones, and this gap widens with time."
To help you keep that biological clock fooled, Runner's World takes a look at the life span of a runner, decade by decade, with advice from medical experts, trainers, nutritionists and amazing runners who define peak performance.