Download The Distribution of Muscle Fibre Types

MUSCLE FIBRE TYPES
 certain muscles and groups of muscles are more adapted to one
energy production system than another
 there are 2 muscle fibre types:
a) slow-twitch muscle fibres
 red or dark in colour
 generate and relax tension relatively slowly
 low levels of myosin ATPase which the body uses to provide
constant energy for muscle contraction
 produce lower tension and/or contraction levels over a long period
of time
 activities: long distance running, swimming, and cycling
b) fast-twitch muscle fibres
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pale in colour
ability to tense and relax quickly
generate large amounts of tension with low endurance levels
high level of myosin ATPase
these fibres can activate at a rate of 2-3 times faster than slow
twitch fibres, therefore, they can perform powerful muscular
contractions
 activities: short sprints, power lifting, explosive jumping
 myoglobin is a protein that stores oxygen and delivers oxygen to
working muscles
 the more a muscle uses aerobic process for energy production, the
more it is able to sustain long-term activity
 therefore, slow-twitch muscles contain high levels of myoglobin,
whereas, fast-twitch muscles are low in myoglobin
3 Fibre Types
1) Type I or Slow Oxidative (SO)
 slow-twitch muscle fibres
 red in colour
 slow contraction
 used in aerobic energy systems
 high concentrations of myoglobin
2) Type II or Fast Oxidative Glycolytic (FOG)
 fast-twitch muscle fibres
 reddish-white in colour
 contraction is moderately fast
 used in anaerobic glycolysis systems
 moderate concentrations of myoglobin
3) Type IIB or Fast Glycolytic (FG)
 fast-twitch muscle fibres
 white in colour
 fastest contraction
 used in anaerobic alactic systems
 low myoglobin concentration
(see chart 5.3 on p.92 in text book)
The Distribution of Muscle Fibre Types
 a muscle’s fibre makeup determines its function
 there are two types of muscles that are described based on their
functions:
a) tonic muscles
 assist the body with maintaining posture or stability
 type I fibres: slow-twitch, cannot function explosively, and
have a considerable endurance capacity
b) phasic muscles
 high percentage of type IIA and type IIB
 explosive movements and low endurance capacity