If you find that you cannot push the turned end through, twist it in the same direction several more times, then try to push it through.
This is done to loosen up the knot. Once it loosens, pull the knot apart with your hands. Do not pull as hard as possible or you might break the knotted material.
Slip the implement of your choice into the knot. Wiggle it back and forth a bit. Without removing the implement you worked into the knot, pull at one portion of the knot to see it if it comes apart. If the knot is still too tight to untie, wiggle the implement you placed in it a bit more, or take it out and try to push something with a slightly wider girth into the space you opened up. Afterwards, try to untie it again.
Be sure that whatever is beneath the knot will not be damaged by the impact.
The amount of time you will need to spend walking or running before your tight knot is loosened sufficiently varies depending on the severity of the knot. Very tight knots will take longer to loosen than knots that are merely tight. Start by walking about for 10 minutes or so, then testing the knot in your shoelace. If it is still tight, walk a bit more.
