Deteriorating telomeres are a bad thing, a sign of aging and disease. Anything that helps to maintain telomere health is essentially a good thing. An anti-aging thing. Previous research has shown that exercise protects telomeres and helps them regenerate. That's a very good thing.
Now German investigators have shown for the first time that endurance aerobic training and interval training promote telomere health, while strength training does not. This doesn't mean you should abandon strength training; you shouldn't. It has many benefits. Among them: It helps protect you from falls.
But as far as total health and anti-aging vigor go, it appears that endurance training beats strength training. As the German scientists point out, early homo probably depended more on running (and even sprinting) for survival than on lifting heavy objects. In their paper, the authors conclude: "Our data support ESC [European Society of Cardiologists] current guideline that resistance exercise should be complimentary to endurance training rather than a substitute."
In the actual prospective, randomized, controlled trial reported in the European Heart Journal, it was shown that endurance training (3 x 45 minutes/week) and interval training (3 x 45/wk) improved markers of telomere health while circuit weight training (3 x 45/week) did not.