Without the Nervous System –
Muscles will not contract.
Sport Books Publisher
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Nerve-Muscle Interaction
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Skeletal muscle activation is initiated through neural activation
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The Nervous system can be divided into central (CNS) and
peripheral (PNS)
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It can also be divided in terms of function: motor and sensory
activity
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Sensory: collects info from the various sensors located
throughout the body and transmits the info to the brain
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Motor: conducts signals to activate muscle contraction
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Activation of motor unit and its innervation systems
1. Spinal cord 2. Cytosome
3. Spinal nerve
4. Motor nerve 5. Sensory nerve 6. Muscle with muscle fibres
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Motor Unit
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Motor nerves extend from the spinal cord to the muscle fibres
Each fibre is activated through impulses delivered via motor end plate
Motor unit: a group of fibres activated via the same nerve
All muscle fibres of one particular motor unit are always of the same
fibre type
Muscles needed to perform precise movements generally consist of a
large number of motor units and few muscle fibres
Less precise movements are carried out by muscles composed of fewer
motor units with many fibres per unit
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All-or-none Principle
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Whether or not a motor unit activates upon the
arrival of an impulse depends upon the so called
all-or-none principle
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An impulse of a certain magnitude (or strength) is
required to cause the innervated fibres to contract
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Every motor unit has a specific threshold that must
be reached for such activation to occur
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5
Intra-muscle Coordination
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The capacity to apply motor units simultaneously
is known as intra-muscle coordination
 Many highly trained power athletes, such as
weightlifters, wrestlers, and shot putters, are able
to activate up to 85% of their available muscle
fibres simultaneously (untrained: 60%)
 Force deficit: the difference between assisted and
voluntarily generated maximal force (trained:
10%, untrained: 20-35%)
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Intra-muscle Coordination cont.
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Trained athletes have not only a larger muscle mass than
untrained individuals, but can also exploit a larger number
of muscle fibres
Athletes are more restricted in further developing strength
by improving intra-muscular coordination
Trained individuals can further increase strength only by
increasing muscle diameter
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Inter-muscle Coordination
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The interplay between muscles that generate movement
through contraction (agonists) and muscles responsible for
opposing movement (antagonists) is called inter-muscle
coordination
 The greater the participation of muscles and muscle
groups, the higher the importance of inter-muscle
coordination
 To benefit from strength training the individual muscle
groups can be trained in relative isolation
 Difficulties may occur if the athlete fails to develop all the
relevant muscles in a balanced manner
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Inter-muscle Coordination cont.
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High-level inter-muscle coordination greatly improves
strength performance and also enhances the flow, rhythm,
and precision of movement
Trained athlete is able to translate strength potential to
enhance inter-muscle coordination
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9
Muscle’s Adaptation to Strength Training
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Individual’s performance improvements occur through a
process of biological adaptation, which is reflected in the
body’s increased strength
Adaptation process proceeds at different time rates for
different functional systems and physiological processes
Adaptation depends on intensity levels used in training and
on athlete’s unique biological make-up
Enzymes adapt within hours, cardiovascular adaptation
within 10 to 14 days
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