There are three types of connective tissue - epimysium, perimysium, and endomysium - that surround and interconnect muscle fibers. The sarcomere is the smallest contractile unit of a muscle, composed of the proteins actin and myosin. Muscle fibers come in two main types - type I (slow twitch) and type II (fast twitch) - and vary in length, number of nuclei, and ratio between individuals. The type of muscle fibers predominantly used depends on the sport or activity, such as type I fibers for marathon running and type II fibers for sprinting. Motor units are composed of a motor neuron and either type I or type II muscle fibers, and vary in size depending

1. Muscle Anatomy 101

2. Three Types of Connective Tissue: Epimysium, Perimysium, and Endomysium

3. Sectional View of a Muscle Fiber

4. Sarcomere Smallest contractile unit Composed of 2 proteins Myosin Actin Run from Z-line to Z-line

5. Interaction Between Actin and Myosin Filaments

6. Muscle Fibers Vary in length Held together by connective tissue Multi-nucleated Two types Type I – high oxidative (slow twitch) Type II – IIa = oxidative-glycolytic (fast twitch) IIx = high glycolytic (fast twitch)

7. Muscle Fibers Hereditary factors vary ratio amongst people Fiber type cannot be changed Exception IIa IIx *not 100% positive

8. Relative Involvement of Muscle Fiber Types in Sport Events Event Type I Type II 100-m sprint Low High 800-m run High High Marathon High Low Olympic weightlifting Low High Barbell squat High High Soccer High High Field hockey High High Football wide receiver Low High Football lineman High High Basketball Low High Distance cycling High Low

9. Motor Units Motor Neuron + Muscle Fibers Type I or Type II Not located adjacent to each other Sizes vary Smaller unit = fewer fibers = more precision Larger unit = more fibers = gross movement

10. A Motor Unit

12. Muscles of the Body Primary movers = agonist Assistant movers = synergists Opposing muscles = antagonists

13. Muscles of the Body Origin = closest to core of body Insertion = furthest from core of body Multiple heads provide fine tune function Spanning over more than one joint allows muscle to serve more than one function