Sports performance is influenced by multiple factors, with genetic factors determining between 20-80% of the variation in different traits such as cardiac performance, oxygen consumption and muscle fiber composition. It is the proportion in the two types of muscle fibers that determines whether we can have a greater or lesser facility to perform power or endurance physical activities.
Muscle performance is the ability of a muscle or group of muscles to perform a repetition effort against resistance. Performing several repetitions of an exercise is a form of muscular performance as is running or swimming. If your muscles have to contract in a similar manner more than once you are using muscle performance.
Among the factors that determine muscle performance are strength, fiber type, training and diet. A larger, stronger muscle can perform the same task under load more times than a weaker muscle. A large muscle also has more glycogen (sugar store used for energy) than a small one so it can sustain a series of contractions or perform a job for a longer period of time.
The composition of muscle fibers is strongly predetermined by the individual's genetics and, therefore, the facility to perform one sporting activity or another. In a sedentary middle-aged person, the percentage of type I or slow fibers is 45-55% (in women this percentage increases slightly).
Sprinters tend to have more type II or fast twitch fibers in the legs while endurance athletes show a predominance of slow twitch fibers. Biopsies in the vastus medialis muscle of the leg reveal that the proportion of fast fibers in throwers and jumpers in track and field, as well as in weightlifters, can be up to 3 times higher than in sprinters.The proportion of fast fibers in the medial vastus medialis muscle can be up to 3 times higher (60% fast fibers) than that of long-distance runners (17% fast fibers) and 50% higher than that of bodybuilders, for example (40% fast fibers).
There are two types of athletes according to the predominant type of muscle fiber: power and sprint athletes (fast fibers) and endurance athletes (slow fibers).
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