To stretch or not to?

"More surprising, when researchers compared the runners’ flexibility scores to their best times in a 10K road race, those with the tightest, least flexible hamstrings tended to be the fastest. They also had the best running economy , meaning that they used the least energy to go the same distance as other runners. Probably , the researchers concluded, tighter leg muscles allow “for greater elastic energy storage and use” during each stride. Think of a rubber band. If it’s overstretched and limp, it doesn’t snap back when pulled and released. So, too, with your hamstrings: If they’re loose, they don’t efficiently lengthen, shorten, and snap back into place with each stride. To some degree, as an endurance athlete you can be as flexible as Morph, or you can be good."