This weekend will see thousands of charity runners taking part in this years London Marathon and engineering researchers may be able to provide some helpful tips as they believe they have solved the riddle of why shoelaces come undone by themselves.

After a detailed study, they discovered that two forces act like invisible fingers, first loosening the knot and then pulling until the laces are left trailing on the ground. They used a slow-motion camera filming a person running on a treadmill to understand how the failure of the knot occurs in seconds after it is triggered by an interaction of complex forces.

It was found that the running foot exerts a force seven times greater when landing on the ground than the one exerted while standing.  This then forces the knot tying the laces together to stretch and relax and loosening it slightly. At the same time, as the knot loosens, the swinging of the laces that occurs as the leg moves forwards and backwards causes an inertial force to be applied on the free ends of the laces, which then pulls the already-loosened knot apart. The researchers believe that this finding could have knock-on uses when applied to other intertwined structures, like DNA for example.

Adding weights to the loose ends of a swinging laces showed that they untied themselves more often, as the inertial forces on their ends were greater. The study also found that, while some laces might be better than others for tying knots, they all suffered from the same fundamental cause of knot failure.

The solution – the typical “Granny Knot” that most of us use is more prone to working itself undone.  Therefore, the consensus online is that a “Surgeons Knot”, which involves running the loop around and through the middle a second time, is the most secure way to tie your shoelaces.

Good luck to all those of you taking part in the London Marathon this weekend!