weekly blog--one for the ages
Learning how to tie your shoes before being able to enter kindergarten was a rite of passage in my hometown. It was the beginning of a lifelong battle to keep the laces from coming apart. Now I know the reason why it happens thanks to a new study by a group of mechanical engineers at UC Berkeley.
The researchers found that when running, your foot strikes the ground at seven times the force of gravity. The knot stretches and then relaxes in response to that force. As the knot loosens, the swinging leg applies an inertial force on the free ends of the laces, which rapidly leads to a failure of the knot in as few as two strides after inertia acts on the laces.
Of course, when a person goes walking or running, their shoelaces don’t always come untied. Tightly tied laces can require more cycles of impact and leg swinging to cause knot failure than one might experience in a day’s worth of walking or running.
For the elderly, lacing up a pair of shoes can present its own challenges. There are many assistive devices available to help. Shoelaces, such as Coilers, are available with coils that never need tying, and there are elastic shoelaces that allow shoes to be slipped on and off without tying and untying. Those who are unable to reach their feet can use a long handle shoe horn, a handicap grabber or push their feet into shoes equipped with elastic self-fastening laces.