![Runner: ready position.](speed_def.png)
Speed is defined as the ability to move a body part quickly.
Speed is the most important aspect of fitness for some athletes like sprinters, sprint swimmers, cyclists and speed skaters.
In many other sports, including team field sports, good speed is also very important as part of the overall fitness profile.
Movement speed requires good strength and power, but also too much body weight and air resistance can act to slow the person down.