By Trevor Mayfield Speed can be broken down to 4 main factors:

1. Agility
2. Endurance
3. Top Speed
4. Acceleration

Agility by definition is the ability to change your direction of movement quickly.  You decide on a movement pattern, and the CNS decides what muscles you need and in what sequence they should be contracted. Once the basic pattern is in place, the CNS can make adjustments by changing the number of muscle fibers involved or the frequency of their stimulation. Therefore, the more you practice the movement the better you get. Endurance is directly affected by the type of muscle fibers that you have specifically trained and developed. It is generally accepted that muscle fiber types can be broken down into two main types: slow twitch (Type I) muscle fibers and fast twitch (Type II) muscle fibers. These distinctions seem to influence how muscles respond to training and physical activity, and each fiber type is unique in its ability to contract in a certain way. Human muscles contain a genetically determined mixture of both slow and fast fiber types. On average, we have about 50 percent slow twitch and 50 percent fast twitch fibers in most of the muscles used for movement. Slow Twitch (Type I) The slow muscles are more efficient at using oxygen to generate more fuel (known as ATP) for continuous, extended muscle contractions over a long time. They fire more slowly than fast twitch fibers and can go for a long time before they fatigue. Therefore, slow twitch fibers are great at helping athletes run marathons and bicycle for hours. Fast Twitch (Type II) Because fast twitch fibers use anaerobic metabolism to create fuel, they are better at generating short bursts of strength or speed than slow muscles. However, they fatigue more quickly. Biomechanically, the human body generates a spring-like reaction through the ankle and legs when sprinting called ground reactive force (GRF) or ground contact force (GCF). According to the USA Track and Field Level 1 Coaching Curriculum (2006), knee drive has a direct relationship to the amount of force applied to the ground. A low knee drive is a result of weak ground contact force. Greater knee drive and an increased stride length are byproducts caused by a greater force being applied to the running surface. By understanding that maximum speed is a product of greater ground contact forces and shorter ground contact times there are many ways you can introduce those concepts into your training. Sprinting involves a quick acceleration phase followed by a velocity maintenance phase. During the initial stage of sprinting, the runners have their upper body tilted forward in order to direct ground reaction forces more horizontally. In order to achieve these high velocities, it has been found that sprinters have to apply a large amount of force onto the ground to achieve the desired acceleration, rather than taking more rapid steps.The muscles responsible for accelerating the runner forward are required to contract with increasing speed to accommodate the increasing velocity of the body. During the acceleration phase of sprinting, the contractile component of muscles is the main component responsible for the power output. Power is defined as the amount of work performed per unit of time. Power is an element of skill-related fitness that is needed to excel in athletic performance. Increased strength does not always translate into increased power. For example, a strong upper body lifts a high amount of weight. However a strong upper body does not always have the ability to throw a shot put very far if enough speed cannot be generated. Explosive power is needed in any athlete who requires hard and fast movement. It is also important to develop power-endurance in many circumstances so that power may be called upon into later stages of fatigue.