Treadmill running with heavier shoes tied to slower race times

It makes sense that running with heavier shoes on will cause you to exert more energy than running with lighter shoes. That was proven several decades ago. But does using more energy while running with heavier shoes translate into slower running times? That's also a yes, say researchers who designed a clever study to show that running times slow when running shoe weight is increased, even if only by a few ounces.