Your skeletal muscular system composes the largest organ in your body. Cells and fibers in your muscular system are embedded in a matrix of collagen that forms tendons, which connect your muscles to bone, according to Muscle Physiology. Your skeletal muscular system allows you to perform physical activity that ranges from daily low intensity activity, to activity that requires intense bouts of energy. Different types of muscle fibers support different kinds of activity.
Muscular Fibers
The contractile and energy producing capacity of different components of your skeletal system determine the primary function of particular components. Your skeletal muscular system consists of three primary muscle fiber components: white fast-twitch, red fast-twitch and red slow-twitch fibers. A particular type of muscle fiber may dominate individual motor units such as your biceps, quadriceps and deltoids. Genetics determine relative concentrations of each type of muscle fiber in your body, according to National Federation of Personal Trainers and Bodybuilding.
Speed and Strength
White fast-twitch motor units in your muscular system are responsible for speed and strength based activities like power-lifting and bodybuilding. Your white fast-twitch muscle fibers contain the highest concentrations of myofibril components. Myofibrils are the contractile components of your muscles. Strong white fast-twitch skeletal muscle supports your ability to perform heavy, intense and low repetition weightlifting.
Endurance
Red slow-twitch motor units function by producing energy over long periods of time for continuous muscular contractions. High endurance activities like marathon running, distance cycling or swimming rely on support from red slow-twitch motor units. Red slow-twitch skeletal muscle tissue contains the highest concentrations of mitochondria. Mitochondria use oxygen to produce muscular energy aerobically. Red slow-twitch skeletal muscle supports your ability to perform daily activities such as walking. Your red slow-twitch muscle fibers adapt to low weight, high repetition resistance training by increasing the amount of mitochondria in these skeletal muscle tissues, notes National Federation of Personal Trainers.
Stamina
The function of red fast-twitch motor units helps you sustain high intensity muscular contractions for longer periods of time. Activities that require physical stamina such as basketball and boxing rely on your red fast-twitch motor units. Red fast-twitch musle fibers contain more balanced concentrations of myofibrils and mitochondria. This skeletal muscle tissue contains fewer myofibrils than white fast-twitch fibers, but more than red slow-twitch fibers. Red fast-twitch tissues also contain more mitochondria than white fast-twitch fibers, but fewer than red slow-twitch fibers.
