A loud bang, the dam bursts, blue liquid tumbles and boils down the streambed and all is swept aside. Fifteen minutes later, a little tongue of water reaches out miles from the site of the event and wets the earth. A new river flows and life follows.

That's what a cross country race looks like! And, none so much as the middle school competition. Hundreds of bodies blocked behind a long white line, building up energy, exerting pressure on the invisible dam as the starter counts down to zero. Then a mass of mid-sized sprinters, each expecting to win the race. A few moments later a line...