You put on your shoes, tie them as firmly as possible, but soon after the laces come undone.

Now scientists think they know what causes one of life’s knotty problems.

They found the force of a foot striking the ground stretches and then relaxes the knot, while a second force caused by the leg swinging acts on the ends of the laces, like an invisible hand.

The researchers say an understanding of shoelaces can be applied to other structures, such as DNA.

Using a slow-motion camera and a series of experiments, mechanical engineers at University California Berkeley found “shoelace knot failure” happens in a matter of seconds, triggered by a complex interaction of forces.

Lead researcher Christopher Daily-Diamond said: “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, that fail under dynamic forces.

“This is the first step toward understanding why certain knots are better than others, which no one has really done.”

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