Telomeres are the endcaps on chromosomes, and telomeric shortening is thought to govern the number of times a cell can divide. The gradual shortening of telomeres through cell divisions leads to aging on the cellular level and may limit lifetimes. A study by Ulrich Laufs, of Saarland University (Germany), and colleagues has found that physical activity has an anti-aging effect at the cellular level, suggesting that exercise could prevent aging of the cardiovascular system.  The team studied two groups of trained professional athletes, one comprised of 32 professional runners, average age 20, from the German National Team of Track and Field, and the other composed of middle-aged athletes with a history of continuous endurance exercise since their youth, average age 51 years, comparing their blood samples with a healthy control group who did not regularly exercise.  The blood cells of the study subjects engaging in long-term exercise training exhibited molecular indicators of reduced aging.  Dr. Laufs commented that: “The most significant finding of this study is that physical exercise of the professional athletes leads to activation of the important enzyme telomerase and stabilizes the telomere,” continuing that: “This is direct evidence of an anti-aging effect of physical exercise. Physical exercise could prevent the aging of the cardiovascular system, reflecting this molecular principle.”