To produce power, you need both Strength and speed. Fortunately, both of these ingredients can be increased through the use of appropriate and systematic training. Individual differences account for much of the variation in how different people respond to specific training. Some very strong genetic factors are clearly associated with speed and power capabilities among individuals.
The most important genetic difference related to power development is the amount of muscle fiber that allows for quick muscular contraction. Your body’s skeletal musculature is made up of several types of fibers. Type I fibers, the so-called slow-twitch (ST) muscle fibers, are associated with less powerful, more enduring functions. These fibers, being more aerobic in nature, take longer to develop force and to fatigue.
Type II muscle fibers, the so-called fast-twitch (FT) fibers, are associated with shorter bursts of explosive action. These fibers, which are used during anaerobic performance, develop force more quickly and fatigue more easily. Type II fibers are further subdivided into Type IIa and Type IIb fibers, with a-types having greater ability for aerobic metabolism and more resistance to fatigue.
The proportion and distribution of FT fibers throughout your body depends to a great extent on your genetic makeup. The average person has an approximate 50-50 split of FT and ST fibers throughout the body. Athletes who excel at power events tend to have a higher percentage of FT fibers, however, and those who excel at endurance events tend to have a higher percentage of ST fibers, compared to the average person.
That leaves many of us somewhere in the middle, perhaps not “natural” stars at either sprinting or long-distance events but capable of improving our performance in either extreme with specialized training. While you cannot do anything to alter the number of ST or FT fibers you were born with, stimulating the FT fibers you do have with explosive training improves their ability to fire or contract powerfully. This is the primary rationale for training for increased power: We can improve our FT fibers.
This is an excerpt from Explosive Lifting for Sports-Enhanced Edition.