How are muscles structured at the most basic level?

Muscles are structured at the most basic level by a hierarchy that begins with individual fibers. Muscle fibers, also known as myocytes, contain myofibrils, which are further divided into sarcomeres—the smallest functional units of muscle contraction. Sarcomeres contain the machinery necessary for muscle contraction, specifically the actin and myosin filaments.

Understanding this hierarchy is crucial in grasping how muscles contract and produce movement. The organization of fibers into myofibrils, and then into sarcomeres, explains the striated appearance of skeletal muscle and their function in producing force. Each level of this organization plays a crucial role in how muscles contract, the efficiency of movements, and muscle growth through resistance training.