structure of skeletal muscle

(muscle cell = fiber)

- each fiber in composed of functional units called myofibrils that run parallel to the axis of the fiber; myofibrils are made up of proteins called actin and myosin

- alternating dark and light bands give muscle its striated appearance,which repeat themselves in the functional unit of skeletal muscle called sacromere

- slow oxidative

- relatively slow speed of shortening

- high oxidative capacity, primarily rely on aerobic metabolism

- high ability to oxidize fat and are fatique resistant

- fast shortening speed

- active primarily on short term high intensity activities; rely on anaerobic metabolism

- Type IIa: fast oxidative glycolytic (FOG) have a high oxidative and anaerobic capacity

-Type IIx: fast glycolytic (FG) have a high glycolytic/low oxidative capacity; fatigue rapidly

- a motor neuron and all the muscle fibers it innervates (controls)

- functional unit of movement

- slow twitch motor units are recruited during lighter effort, and for more powerful movements there is a progressive activation of the more powerful fast twitch IIa and the IIx units

- if intensity high enough acid production in muscle contributes to fatique

- muscle activated but the force is exerts is equal to the force resisting and there is no change in joint angle

- sometimes used to improve points of poor mechanical advantage and in rehab settings

- change in joint angle

- Concentric (shortening): decrease in joint angle, a muscle action involving moving in the opposite direction of the external force (ie, raise arm againt gravity)

- Eccentric(lengthening): increase in joint angle, a muscle action involving moving in the same direction of ext force but slower than ext force