In order to understand the section before this, you must be familiar with kinetic and potential energy...

Kinetic Energy

Kinetic energy is the amount of energy that an object has at any given moment. It can be represented in the equation K = 1/2mv^2, where m represents mass and v represents the velocity of the object. This means that kinetic energy is directly proportional to the objects mass (If two runners were sprinting at the same velocity, the runner with more mass would contain more kinetic energy than the smaller one). Kinetic energy is also proportional to velocity (the faster the runner, the more kinetic energy he/she possesses). Kinetic energy is measured in joules (J).

Potential Energy (Stored Energy)

There are different types of potential energy. In general, potential energy means that the energy is "stored" and can be used, or converted, into kinetic energy. If you think back to the previous section about pendulums, I mentioned that as you swing your legs up, it creates potential energy. You are moving your legs against gravity, therefore creating gravitational potential energy. One can represent gravitational potential energy by the equation U(g) = mgh, where m represents mass, g represents gravitational pull, and h represents the height of the object.

In the case of sprinting, think about the potential energy of the runners legs. As the leg is swung back and forward, at the peak height is when he or she has the most potential energy. The amount of the potential energy is proportional to the peak height that the knee reaches, there fore the higher the knee, the more potential energy. Thus, with more potential energy, the more kinetic energy can be converted. The result: a faster runner.