Biochemical

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Biochemical Contractile
Properties of Muscle
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Biochemical Properties of Muscle
1. Oxidative Capacity
2. Type of ATPase Isoform
Oxidative Capacity
Determined by
1. of mitochondria within the fibre (cell)
2. of capillaries surrounding the fibre
3. amount of myoglobin in the fibre
- more mitochondria ? more ATP generating
capacity (aerobic)
- more capillaries ? increases oxygen to the
fibre during contraction
- more myoglobin ? more oxygen binding capacity
resulting in more oxygen available to the
mitochondria and therefore, a higher aerobic
capacity and more fatigue resistance
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Biochemical Properties of Muscle
1. Oxidative Capacity
2. Type of ATPase Isoform
ATPase Isoform
Many isoforms of ATP exist, and they differ in
their activity
(i.e. the speed they catabolize ATP)
- ATPase isoforms with high ATPase activity
degrade ATP rapidly ? rapid muscle contractions
- ATPase isoforms with low ATPase activity ? slow
muscle contractions
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Contractile Properties of Muscle
1. Maximum Force Production
2. Speed of Contraction
3. Efficiency
Maximum Force Production
Force Produced
Specific tension
Fibre Cross-sectional area
Contraction Speed
- the highest speed at which a fibre can shorten
(rate of cross-bridge cycling)
- Vmax depends on ATPase activity
(higher ATPase activity ? higher Vmax)
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Contractile Properties of Muscle
Efficiency
Energy input (ATP used)
Muscular efficiency
Energy output (work done by muscle)
- more efficient muscles require less energy
input to perform a certain amount of work
- type I (slow twitch) fibres develop less
tension and are more efficient than type IIB
(fast twitch) fibres
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Fibre Types

Related Functions
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Fibre Types
Type I (Slow Twitch)
Type IIB (Fast Twitch)
Type IIA (Fast Twitch)
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Type I - Slow Oxidative(SO)
Slow oxidative or slow twitch muscle fibres
appear red due to myoglobin content.
? contain large of mitochondria
? more capillaries (surrounding)
5 - 500 fibres per motor unit
? more myoglobin (oxygen store)
? fewer fibres per motor unit
? low Vmax (slower contraction rate)
? greater efficiency
Result Greater capacity for aerobic metabolism
and high resistance to fatigue
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Type IIB - Fast Glycolytic (FG)
Fast Glycolytic or fast twitch muscle fibres
appear white due to deficit of myoglobin.
? contain fewer mitochondria
? limited capacity for aerobic metabolism
5 - 2000 fibres per motor unit
? large of glycolytic enzymes
? high Vmax (fast contraction rate)
? lowest efficiency of all fibre types
? more force produced due to greater of fibres
per motor unit
? more developed sarcoplasmic reticulum
Result Greater capacity for anaerobic
metabolism, greater power and less
resistance to fatigue
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Type IIA - Fast Oxidative Glycolytic (FOG)
? intermediate fibres
(characteristics b/w type I and II)
? fast oxidative, glycolytic fibre characteristics
? adaptable with endurance training to increase
oxidative capacity levels equal to type I fibres
Some muscle groups have predominantly one type of
fibre or the other. However, most muscle groups
contain equal numbers of both fast and slow
twitch fibres.
The percentage of fibre type depends on
1. Genetics
2. Blood level of hormones
3. Exercise habits
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Type I II Fibres
Type I fibres dark Type II fibres light
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Table 5.3Characteristics of different muscle
fibre types
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Muscle Type and Fibre Type
Tonic muscles
Muscles that assist in maintaining posture or
stability while sitting, standing or during other
types of movements.
- contain high percentage of slow twitch fibres
(high endurance, low explosive capability)
e.g. erector spinae, rectus abdominus, soleus,
forearm muscles
Phasic muscles
Muscles involved in powerful movements such as
lifting, jumping.
- containing large percentage of high twitch
fibres
(low endurance, high explosive capability)
e.g. bicep brachii, quadriceps, gastrocnemius
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Fibre Types and Performance

• Studies have shown no sex or age differences in
  fibre distribution

• Average nonathlete possesses 47 53 (approx.
  equal amts) of
• slow or fast twitch fibres

• It is believed that successful elite athletes
  have widely disparate
• numbers of slow/fast fibres as shown in the
  table below

Typical Muscle Fibre Composition in Elite Athletes
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Activity and Motor Unit Recruitment
Muscles consist of motor units. Motor units
consist of a motor neuron and all the muscle
fibres (cells) that are connected to it. Because
all of the muscle fibres of one motor unit are
attached to the same motor neuron, they are
subject to the same stimuli and therefore must be
the same fibre type (all-or-none).
Motor units containing Type I (SO) fibres have
lower threshold stimuli and therefore are more
easily contracted.
e.g. When walking, motor units in the quadriceps,
hamstrings, and calves containing type I
fibres are stimulated to contract first. They
can continue to contract for long periods of time
(great aerobic capacity).
When the walk breaks into a jog and then a run,
the type I fibres cannot continue to function at
that level, a stronger stimuli results in the
recruitment of motor units containing type II
muscle fibres. These fibres are very powerful
but cannot continue to function for a long period
of time (low aerobic capacity) before
insufficient energy and a buildup of lactic acid
results in muscle fatigue.
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Activity and Motor Unit Recruitment
Therefore, motor unit recruitment is progressive,
with motor units containing type I fibres and
having a lower threshold stimulus always being
recruited first. These units are responsible for
smaller, more tactile movements requiring less
force and possibly of a longer duration.
Whether motor units containing type II fibres are
recruited and how many are recruited depend on
the amount of force necessary for an activity.

The greater the force necessary, the more type II
motor units recruited.
Type I motor units ALWAYS RECRUITED FIRST!
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Force Regulation in Muscle
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Force Regulation in Muscle
Factors responsible for regulating force during
muscle contractions
1. Number and type of motor units recruited
2. Initial length of muscle at time of contraction
3. Nature of neural stimulation
Number and type of motor unit recruited
- More motor units recruited ? more force (vice
versa)
- Fast twitch ? more force
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Force Regulation in Muscle
Initial length of muscle at time of contraction
Less than Optimal length
Greater than Optimal length
Optimal length
No cross-bridge interaction no tension
development
Maximal cross-bridge interaction max. tension
development
Fewer cross-bridge interactions reduced tension
development
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Force Regulation in Muscle
Nature of neural stimulation
Sustained muscle contractions occur because of
rapidly repeating neural impulses from the motor
neurons to the muscle fibres they innervate
(motor units). Neural impulses do not arrive at
the same time to all of the units. Some motor
units are contracting, while others are relaxing.
The first few contractions of muscle fibres are
twitches. As frequency of stimulations is
increased, the muscle does not have time to relax
between stimulations, and the force appears to be
additive. The response is called summation. If
frequency of stimulation increases futher,
individual contractions are blended in a single
sustained contraction called tetanus.
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Muscle Hypertrophy, Atrophy and Hyperplasia
Hypertrophy -
Muscle growth in response to overload training
Transient hypertrophy (pump) -

increase in fluid (blood)
accumulation to a specific muscle exercised. The
effects are temporary with the blood leaving the
muscle soon after completion of exercise.
Chronic hypertrophy -

increase in muscle size as a result of
1. Increased capillary density
2. Increased actin and myosin
3. Increased storage capacity for glucose,
glycogen, ATP and creatine phosphate
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Muscle Hypertrophy, Atrophy and Hyperplasia
Atrophy -
The shrinking of muscle in size and strength due
to lack of exercise, malnutrition or disease
Form of muscle growth that involves the splitting
of muscle fibres into daughter cells. The
process occurs in animals but has not been shown
to take place in humans
Hyperplasia -
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