• The brain controls motor units, and motor units innervate muscle fibers
• The number of motor units varies from muscle to muscle and a single motor unit can inebriate anywhere from 2-3 fibers up to several thousand muscle fibers.
• Actin and myosin are the “base” contractile components that make up a sarcomere
• A series of sarcomere create myofibril, which is bundled by tissue called sarcolemma, which form a single muscle fiber. Muscle fibers are bundled by tissue called fascicles, that bundled together form skeletal muscle.
• Actin and Myosin produce force through continual crossbridging, pulling, and releasing.
• Concentrics are more energy taxing. (More metabolic byproduct)
  Eccentrics cause more muscle damage, require less metabolic expenditure, and involve more passive tissue.