slow-twitch and fast-twitch muscle...
TRANSCRIPT
Slow-Twitch and Fast-Twitch Muscle Fibres
© 2015 Thompson Educational Publishing, Inc.
Certain muscles and muscle groups are
more adapted to one energy production
system than another. Exercise
physiologists find it useful to distinguish
different kinds of muscle fibres:
• Slow-twitch muscle fibres are red or
dark in colour, and generate and relax
tension relatively slowly. The trade-off is
that they are
able to maintain a lower level of tension for
long durations.
• Fast-twitch muscle fibres are more pale in
colour, have the ability to tense and relax
quickly, and can generate large amounts of
tension with relatively low endurance levels.
The Role of Myoglobin in Sustaining Energy-Producing Reactions
© 2015 Thompson Educational Publishing, Inc.
The differences in muscle fibre types are due mainly to the
extent to which a muscle relies on oxygen in the production of
energy.
•The protein myoglobin is the oxygen storage unit that
delivers oxygen to working muscles, thereby enabling
energy-producing reactions to be sustained over a
long time period.
•Slow-twitch, red muscle fibres are high in myoglobin
and ideal for endurance activities.
•Fast-twitch fibres (with low myoglobin
concentrations) are more adapted to shorter bursts
of effort.
Myoglobin
Comparison of Fibres
Muscle Fibre Types and Physical Activity
© 2015 Thompson Educational Publishing, Inc.
Slow-twitch muscle fibres
These are ideal for activities
such as long- distance
swimming, cycling, and
running.
Fast-twitch muscle fibres
These can activate at a rate two to
three times faster than slow-twitch
muscles, making them ideal for
the fast, powerful muscle
contractions needed for activities
such as short sprints,
powerlifting, and explosive
jumping.
Type I Fibres
[Slow-Oxidative (SO) Muscle Fibres]
© 2015 Thompson Educational Publishing, Inc.
Kinesiologists distinguish not just two but three different types of
muscle fibre, using a combination of tension-generating features and
the metabolic properties of the fibre.
Type I or slow-oxidative (SO) muscle fibres generate energy slowly,
are more fatigue- resistant, and primarily depend on aerobic
processes.
Type IIA Fibres
[Fast-Oxidative Glycolytic (FOG) Fibres]
© 2015 Thompson Educational Publishing, Inc.
Type IIA or fast-oxidative glycolytic (FOG) muscle fibres are intermediate-type muscle fibres.
• They allow for high-speed energy release as well
as glycolytic capacity.
Type IIB Fibres
[Fast-Glycolytic (FG) Muscle Fibres]
© 2015 Thompson Educational Publishing, Inc.
Type IIB or fast-
glycolytic (FG)
muscle fibres
store lots of
oxygen and
sufficiently high
levels of enzymes
necessary for
quick contraction
without requiring
oxygen.
© 2015 Thompson Educational Publishing, Inc.
Feed Me!
Type 1: They rely on their legs to get
them around. The active muscles, such
as the legs and thighs, are full of blood
vessels. These blood vessels contain
myoglobin (or muscle hemoglobin), which
delivers oxygen to the muscles. The
more myoglobin the muscles contain, the
darker the muscle.
Type 2: white meat is the result of well-
rested muscles. The breast muscles,
which are used for flying, are hardly used
by turkeys. There is no need to have a
rich supply of oxygen delivered to these
muscles.
Determining your fibre type
1 RepMax
number of reps at 80% muscle fiber type
< 7 > 50% fast twitch (FT)
7 to 12 equal proportion of fiber type
> 12 > 50% slow twitch (ST)
MUSCLE BIOPSY
Implications for Training
For elite athletes, differences in muscle fibre types are often very pronounced. Olympic sprinters, for example, may possess as muchas 70-80 percent fast-twitch muscle fibres.Athletes in marathon-style events may possessthat equivalent in slow-twitch fibres.
• But many factors
contribute to an
individual’s athletic
performance.
• Physiology is just one
of them.
© 2015 Thompson Educational Publishing, Inc.
The Puzzle of East Africans’ Dominancein Distance Running
For some time now, athletes from Kenya and Ethiopia have dominated long-distance running.
• These countries
typically account for
medals in the 5000 m,
the 10 000 m, and the42.2 km marathon.
• The achievement of
these runners is one of
the most puzzling and
most studied topics in
sport science.
© 2015 Thompson Educational Publishing, Inc.
Consistently Outstanding Resultsfor East African Men and Women
© 2015 Thompson Educational Publishing, Inc. 60
On the men’s side, the world records in competitions ranging from the 800 m to the marathon show that 17 of 21 records are held by East Africans.
• On the women’s side, Ethiopian Triunesh Dibaba
won gold at the 2012 Olympics in the 10 000 m,
and two Kenyan women won silver and bronze.
• In the 5000 m event in London, Dibaba’s teammate
Mesaret Defar won gold, with Vivian Cheruiyot
placing second and Dibaba placing third. (Dibaba
had also won the 10 000 m race at the 2008
Olympic Games in Beijing.
Victory for Kenya & Ethiopia at the World Athletics Championships, 2011
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Possible Physiological andCultural Explanations
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• Some researchers theorize that these athletes’ bodies have a
higher capacity to take in and use oxygen—a capacity known as
“VO2 max.”
• Others argue that low overall body fat, long legs, and low resting
heart rates help these athletes run faster, longer, and more
efficiently.
• Children in Kenya and Ethiopia tend to walk and run
everywhere, thus building up a strong background in long-
distance running.
• Budding athletes in these countries often see running as a
means of supporting their families through prize money and
endorsements.