In physical education, speed is defined as the maximum frequency at which an individual can cover a distance or make a movement in a specific period of time. It is one of the main components of physical fitness and is important for success in many sports. Speed is not just how fast someone can run, but is dependent on acceleration, maximal speed of movement, and speed maintenance. Movement speed requires good strength and power, but also too much body weight and air resistance can act to slow the person down. Speed can be improved through training focusing on strength and technique, although some factors may limit speed, such as inherited characteristics, body type and size, and the duration of the event in which one is participating. Some of the sports that emphasize speed include athletics, swimming, skating, hockey, cycling, basketball, football, tennis, boxing, and martial arts, among others.