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Human Body Systems
Lesson 21 Terms and Definitions
Q: Why do muscles get
tired?
Muscle Fatigue
Muscle Fatigue – the reduced ability of a
muscle to contract.
http://run4change.files.wordpress.com/2009/04/exhuasted-runner1.jpg
http://shakeout.files.wordpress.com/2008/11/tired_runner.jpg
Muscle Fatigue
Why?
1. Muscles need energy (ATP) from cellular
respiration
2. Fatigue happens when… ATP produced
cannot keep up with ATP needed by
muscles
Light exercise
• Aerobic respiration can produce most of
the ATP energy needed for light exercise.
• When there’s not enough Oxygen present,
Anaerobic Respiration occurs.
– Lactic acid builds up, causing fatigue
– Lactic acid is washed out of muscles within 30
minutes after exercise.
Muscle Fatigue
• Avoid fatigue by training and practicing.
Slow Twitch Muscles
• Muscle fibers are slow to contract
• Endurance
• More mitochondria, more myoglobin
– Myoglobin – reddish protein that
stores O2 and gives muscle fibers
color.
• Found in Athletes that sustain a
moderate level of activity for
extended periods of time. Ex.
Cyclist, marathon runners, etc.
http://z.about.com/d/bicycling/1/0/6/1/-/-/71398008.jpg
Fast Twitch Muscles
• Fibers contract
rapidly
• Fewer Mitochondria,
Less myoglobin
• Found in: athletes
that do rapid activites.
Ex. Weight lifters,
sprinters.
http://www.baspeed.com/userfiles/sports/lianalambert%20weightlifter.jpg
Fast
Slow
Chickens/Turkey
White/Light meat
Don’t fly
Fast Twitch Fibers
Less endurance
Less myoglobin
Ducks
Dark meat
Fly A LOT!
Slow Twitch fibers
Lots of endurance
More myoglobin
A CRAMP!!!
AAAAHHHHH A
MUSCLE CRAMP!!!
A cramp
• Cramp – a sustained muscle contraction
of a muscle group.
– WHEN: during/following exercise/NO
apparent reason.
– CAUSES: could be low blood sugar,
electrolyte depletion (sodium/calcium), and
dehydration
Q: How do muscles
contract?
Muscle Contractions
1. Nerve sends a signal to muscle
2. Actual Contraction (2/3’s its size).
3. Relaxation
Contraction takes
approx. 10-100 milliseconds!!