For such an age-old problem, it's gotten surprisingly little scientific study. But now physicists at Berkeley think they've figured out why the knots of our shoelaces come untied, reports the BBC. Through slow-motion video, they found that it's a complex combination of stomping (your foot hitting the ground) and swinging (your leg gearing up for the next step). The forces exerted on the laces are surprisingly high, "more than twice the g-force astronauts feel during a typical rocket launch," in the words of the Christian Science Monitor. And the unraveling happens in two stages: a slow, gradual weakening followed by sudden failure. The scientists say the work has grand implications, but ordinary folks may be more interested in a takeaway noted at Science: The research confirms that square knots are better than the familiar "granny" knots many people use.
"I've been tying it a new way for about two years now," grad student Christine Gregg, whose running was captured in the video, tells NBC News of her switch to square knots. (A slew of websites explain how to tie one, and Science also directs people to this TED Talk.) The study is published in the Proceedings of the Royal Society A, and researchers say it's "far from exhaustive" in that it doesn't take into account factors such as shoelace material. But as for those grand implications: "When you talk about knotted structures, if you can start to understand the shoelace, then you can apply it to other things, like DNA or microstructures," says co-author Christopher Daily-Diamond. The study is the "first step toward understanding why certain knots are better than others, which no one has really done." (Another study found that running might actually make knees healthier.)