Skeletal muscles are made of cellular units called muscle fibers because of their shape. The fibers contain contractile structures – myofibrils which are made of thick and thin protein filaments which are arranged in specific units sarcomeres. During the muscle contraction these filaments slide over each other by the means of so called myosin cross-bridges. The skeletal muscles consist of different types of muscle fibers which are adapted either for endurance or for strength. The skeletal muscles when stressed adapt and improve their function. The fundamental adaptation to resistance training is an increase in muscle mass. This occurs primarily by enlargement of the muscle fibers – hypertrophy. The benefit of increased cross-sectional area is an increased ability to generate force. Numerous studies have shown that fast-twitch fibers show greater increases than slow-twitch fibers. Recently, considerable evidence has indicated that the enlargement of the muscle may be the result not only of the hypertrophy of existing fibers but also of an increase in fiber numbers – hyperplasia.

Temeljne medicinske znanosti