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Unformatted text preview: Slow-twitch muscle fibers
Fast-twitch muscle fibers • “Oxidative” or “red” muscle.
• Contain myoglobin: oxygen binding protein.
• Contain many mitochondria. ! • Are well-supplied with blood vessels.
• Maximum tension develops slowly, but is highly
resistant to fatigue. ! What Determines Muscle Strength and Endurance? ! Slow-twitch fibers have reserves of glycogen and
fat; can produce ATP as long as oxygen is
Muscles with high proportion of slow-twitch fibers
are good for aerobic work (e.g., long distance
running, cycling, swimming, etc.)
! What Determines Muscle Strength and Endurance? ! Fast-twitch fibers: • “Glycolytic” or “white” muscle.
• Fewer mitochondria, fewer blood vessels, little
or no myoglobin. • Develop greater maximum tension faster, but
fatigue more quickly. • Can’t replenish ATP for prolonged contraction. ! Type I (slow; dark fibers) and Type II (fast; light fibers) human skeletal muscle. LM. Slow-and Fast-Twitch Muscle Fibers (Part 1) Distance cyclist Sprinter ! ! Slow-twitch Fast-twitch ! ! What Determines Muscle Strength and Endurance? The proportion of fast- and slow-twitch fibers in
skeletal muscles is determined mostly by genetic
heritage. Training can alter muscle properties to a certain
! What Determines Muscle Strength and Endurance? Exercise:
• Anaerobic activities increase muscle strength:
new actin and myosin filaments form, muscle
• Aerobic activities increase endurance: oxidative
capacity is enhanced by increasing number of
mitochondria, blood vessels, myoglobin, and
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This note was uploaded on 02/13/2014 for the course MCDB 1B taught by Professor Weimbs during the Winter '08 term at UCSB.
- Winter '08