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TYPES OF MUSCLE CONTRACTIONS
 Isometric contraction: when the ms. does not shorten during
contraction while tension is increasing.
 Isotonic contraction: when the ms. shortens or lengthens
while the tension on the ms. remains constant
Isotonic (static) Contraction
Isometric (Dynamic) Contraction
Tension is constant
Tension n the ms. Rises markedly
Length is decreased or lengthened
Length of the ms. is constant
External work is done
No work is done
Mechanical efficiency = 25%
Mechanicl efficiency = 0
Long duration
Short duration
less energy used/contraction
More energy used/contraction
Contraction occurs when the legs are Contraction occurs during standing
moved in walking
to maintain posture against gravity
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Types of Isotonic (static) Contractions:
 Concentric: the muscle shortens, e.g. contraction of the biceps
to produce elbow flexion.
 Eccentric: muscle lengthen or is stretched while contracting,
e.g. lowering a load on the ground.
Tension Variation
1. Passive tension: tension developed in the ms. length is
increased while is not stimulated ( i.e. concentric
contraction).
2. Total Tension: tension that a ms. develops when stimulated
to contract isometrically.This tension also vary with the
change of the initial length.
3. Active tension: is the difference between the total tension
and the passive tension at any length( the amount of
tension) actually generated by the contractile process.
 Tension increases with an increased length, but overstretch
may lead to weakness of the muscle.
 Rupture of the muscle occur when it is stretched to about 3
times its equilibrium length of the relaxed muscle cut from its
bony attachment.
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Types of Skeletal Fibers :
1. Slow Oxidative or Type 1 Fibers:
 In postural ms. as can maintain contractions for long periods.
 Red fibers
 Produces ATP with high efficiency.
 Has a large number of mitochondria & mitochondrial enzymes.
 Has aerobic energy transfer.
 Is innervated by small motor neurons that activate small
number of fibers
2. Fast Oxidative or Type II a Fibers:
 Are moderately resistant to fatigue.
 Have mytochondrias & considerable amount of myoglobin.
 Moderately red fibers.
 Moderately well developed capacity for aerobic & anaerobic
energy transfer.
 Intermediate motor neuron, its activities are e.g; middle
distance runnng, swimming,…
3. Fast Glycolitc or Type IIb Fibers:
 Rely on anaerobic glycolysis.
 Become fatigued easily.
 Few mitochondria.
 Little myoglobin → white fibers.
 Specialised in powerful, brief types of contractions.
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– Large motor neurons that activate large number of fibers
for heavy loads.
– Mixed with other muscle fibers as in limb muscles, eye
and finger muscles.
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