Slow-twitch simply means that these fibers contract at a relatively slow rate of speed. People with a lot of slow-twitch fibers make good endurance runners, swimmers, and cyclist. They are the ones that usually turn out to be the best football, basketball, and baseball players. The only problem with high fast-twitch composition is that they fatigue rather quickly. In other words, they don t possess a lot of endurance.
Training has no affect on fiber ratio.
You have what you are born with, i.e., the ratio is genetically determined. In general, strength is determined by the number of fibers contracting and the frequency of muscle fiber stimulation. The frequency of muscle fiber stimulation refers to the influence the nerve impulse has on force production. The greater the frequency of firing of the nerve from the brain, the greater the force. All of this is determined by the demand placed on the muscular system.