Most athletes have never heard the word "telomeres", but as you age and want to stay completive telomeres become a very important term behind the scenes in human performance. Telemores are protective caps on the ends of your DNA strands and have an effect on how rapidly cells age. As we age the telomeres shorten, structurally they weaken, and cells age and die faster. Shorter telomeres are now associated with many forms of health issues including cancer, stroke, cardiovascular disease, diabetes etc.
There is a German study (reported in the New York Times) as well as others that showed that highly active runners over 50 had maintained telomere length close to highly active runners in their 20s. When compared to the sedentary population over 50 the sedentary crowd has shortened telomere length by about 16% suggesting that endurance training had kept the cells in excellent condition. In some Euro countries that think out of the box with regards to maintaining good health (unlike America) there's a serious push for Telomere testing. Unfortunately many people seem to gravitate to slower and less stressful activity levels over time as if we’ve somehow earned it, hopefully over time this mentality will change. Here's a link to an excellent article by Joel Friel as he explains in depth the relationship with exercise and Telomere health. http://www.joefrielsblog.com/2013/09/aging-an-excuse.html