Q: Why do my shoelaces untie so easily when I run?

A recent study at the University of California-Berkeley answered this exact question. The researchers used slow motion cameras to record what happens to shoelaces as a test subject ran on a treadmill. The video revealed that laces untie due to a combination of two forces. A runner’s foot strikes the ground at seven times the force of gravity, which causes the knot to stretch and then loosen. Meanwhile, the swinging leg whips the free ends of the laces forward. The result is the laces are slowly being pulled outward in the same way that you untie your shoe by pulling on the ends. When researchers attached weights to the ends of the laces to test that concept, laces untied even faster.

So what’s a runner to do? For one, start with the proper knot. A common shoelace bow tie knot can be tied in two ways. The stronger version of the knot is based on a square knot, with the two laces crossings done in opposite directions. (Google “reef knot” for precise instructions.) The other version, known as a false knot, the laces crossings are done in the same direction, causing the knot to twist instead of laying flat. And of course, double-knotting helps to reduce the risk of untying as does tucking the lace ends under the laces further down on the shoe.