Explanation:
Assuming we can turn on the lightbulb from any distance with a device. We can gradually increase the distance that separates us from lightbulb, in this way, if the speed of light is finite we can see a temporary delay between the moment we turn on the lightbulb and the moment in which we observe its light.
The end or finish of an event or process.
There are two interchangeable concepts that can be applied to this theory. The first one is the moment of Inertia and the second the perioricity. When the runners put their leg forward they reduce their moment of inertia allowing their center of mass to maintain the speed they carry and not waste energy. In this way when they swing, the leg begins to act as a kind of pendulum, and remember that the pendulum is directly proportional to the length, that is,

In this way, by bringing their legs closer they reduce the distance and make the period shorter.