Term
| Structure of Skeletal Muscle |
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Definition
| each fiber (muscle cell=fiber) is composed of functional units (myofibrils) that run parallel to the axis of the fiber. Myofibrils are made up of proteins called actin and myosin. The sarcomere is the larger section of the muscle encompassing the myofibrils and muscle fibers. |
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Term
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Definition
| a muscle shortens or lengthens as the strands of actin and myosin slide past each other without actually changing length. Little myosin "hands" (crossbridges) attach and pull the actin strands using energy provided by ATP. |
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Term
| Excitation-Contraction Coupling |
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Definition
| mechanism whereby electrical impulses initiated in the brain & transmitted to the muscle begin the chemical events at the muscle cell surface and cause calcium to be released from stores inside the muscle, which ultimately causes the muscle to contract. It is calcium that allows the myosin "hands" to be bound to the actin strands and pull them towards each other, contracting the muscle. |
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Term
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Definition
| slow oxidative (SO), relatively slow contracting speed compared to Type II, high oxidative capacity (primarily rely on aerobic, or fat metabolism), large & numerous mitochondria (cell compartment where aerobic metabolism occurs), highly vascularized w/high myoglobin content (protein that holds oxygen at the tissue), and high ability to oxidize fat/fatigue resistant. |
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Term
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Definition
| fast shortening speed, active primarily during short-term, high intensity activities to generate powerful contractions; rely primarily on anaerobic, or carbohydrate metabolism for energy. |
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Term
| Type IIa - Fast Oxidative Glycolytic (FOG) |
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Definition
| subdivision of Type II muscle fiber that have high oxidative (aerobic) & anaerobic capacity |
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Term
| Type IIx/IIb - Fast Glycolytic (FG) |
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Definition
| second subdivision of Type II muscle fiber that have high glycolytic/low oxidative capacity and fatigue rapidly. |
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Term
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Definition
| motor neuron and all the muscle fibers it controls; the functional unit of movement, each muscle fiber receives input from only one neuron. Motor units are composed of fibers of ONE fiber type w/similar metabolic profile & fire in an all-or-none manner. The force of muscle action is raised by increasing the number of motor units "recruited" in muscles used for an activity. |
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Term
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Definition
| process of adding more motor units to increase a muscle's force. As the muscle force requirement increases, larger motor units are recruited (size principle). Motor units are selectively recruited to produce the desired force output i.e. lifting a barbell vs. a small object. Slow-twitch units are recruited during lighter effort & for more powerful movements stronger fast-twitch IIa and then IIx units are activated. |
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Term
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Definition
| muscle is activated but force it exerts is equal to the force it is resisting & there is no change in joint angle; used to improve points of poor mechanical advantage & for rehabilitation. |
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Term
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Definition
| change in joint angle - increase (lengthening) or decrease (shortening) in joint angle depending on muscle action type. |
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Term
| Shortening (Dynamic Muscle Action) |
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Definition
| concentric (decrease in joint angle) - muscle action involving moving in the opposite direction of the external force i.e. raise arm against gravity. |
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Term
| Lengthening (Dynamic Muscle Action) |
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Definition
| eccentric (increase in joint angle) - muscle action involving moving in the same direction of the external force and slower than external force i.e. lower arm with gravity. |
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