Transcript Muscles at Work - Dufferin-Peel Catholic District School Board

Muscles at Work
Chapter 4
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Objectives
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To be able to identify and describe the
different types of muscle contractions
To identify the components of strength
To gain an understanding of the
relationships among strength components
To describe the factors that influence
strength development
To evaluate resistive force and power
patterns of exercise devices
To analyze sports movements and make
movement-oriented exercise prescriptions
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Types of Muscle Contractions
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Types of Muscle Contraction
Forms and types of muscle contraction
Dynamic
Static
Isometri
c
Concentric Eccentric
Isotonic
Auxotonic Isokinetic Plyocentric
Concentric Eccentric
(overcoming,
accommodating) (resistive)
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Types of Muscle Contraction
Forms and types of muscle contraction
Static
Dynamic
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Types of Muscle Contraction
Forms and types of muscle contraction
Static
Isometric
Concentric
Eccentric
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Types of Muscle Contraction
Forms and types of muscle contraction
Dynamic
Isotonic
Auxotonic
Isokinetic
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Plyocentric
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Types of Muscle Contraction
Dynamic
Isotonic
Auxotonic
Isokinetic
Concentric
Eccentric
(resistive)
(overcoming,
accommodating)
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Plyocentric
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Types of Muscle Contraction
Forms and types of muscle contraction
Dynamic
Static
Isometri
c
Concentric Eccentric
Isotonic
Auxotonic Isokinetic Plyocentric
Concentric Eccentric
(overcoming,
accommodating) (resistive)
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Static Contraction
 Muscle
tension or internal force
exerted against an external load
 Internal force is equal to, or
weaker than, the external load
 No visible movement of the
external load occurs
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Static Contraction
 In
most sports, the need for
maximal static contraction is
rare
 Maximal static contraction is
most often seen in gymnastics,
wrestling, and judo
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Activities Requiring Maximal
Static Muscle Tension
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Static Contraction
 Most
sports require low to submaximal static contraction
 Examples of sports that require
this type of contraction include
sail-boarding, alpine skiing, and
shooting events
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Activities Requiring
Sub-Maximal Static Muscle Tension
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Dynamic Contraction
 Muscle
tension or
force is exerted
against an external
load
 Internal force exerted
is greater than the
external load
 Visible movement of
the external load
occurs
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Isometric Contraction
A static contraction
 Muscle contraction against an external
force
 No visible change in muscle length
 External load is greater than the force
generated by the internal force
 No external movement occurs
 No work is performed because no
movement occurs
 A high amount of tension is developed,
energy is used
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Pushing against a stable wall is an
example of an isometric
contraction
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An isometric contraction occurs
during an arm wrestling match
when opponents generate equal
forces
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Auxotonic Contraction
A dynamic contraction
 During dynamic work, continual
changes in joint angle and speed result
in changes in strength needs
 That is, the tension required to move
an external load varies
 The involvement of more or less motor
units allows the muscle to adapt to
changing tension requirements
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Auxotonic Contraction
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1.
2.
3.
4.
For example, the strength
needed to perform a barbell
curl depends on a number of
internal factors
These factors include:
The athlete’s physique
The athlete’s leverage
The angle position of the
limbs
The speed of the movement
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Auxotonic Contraction
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Although the weight of the barbell remains
the same, these factors may compromise
an athlete’s capacity for strength gains at all
joint angles
 Therefore, it is not easy to gain equal
strength gains at all joint angles when
training with free-weights alone
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Isotonic Contraction
 A dynamic
contraction
 A change in muscle length occurs
 Constant tension is achieved and
maintained
 Rarely encountered in sports and
athletic events because a change
in tension is usually required with a
change in joint angle
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Isotonic Contraction
 Lowering
a heavy weight at a slow
and constant speed is an example
of an isotonic contraction
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Isokinetic Contraction
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A dynamic contraction
Involves a constant speed contraction
against a preset high resistance
Generation of a high level of tension within a
muscle at all joint angles
Thus, muscle strengthening also occurs at
all joint angles
With the use of certain machines, constant
tension can be achieved as joint angle and
movement velocity are controlled
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Isokinetic Contraction
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Examples of dynamometers that
allow for isokinetic contraction
include:
CYBEX
2. KINCOM
3. LIDO
4. HydraGym
5. Nautilus
1.
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Concentric and Eccentric Contractions
Concentric Contraction:
Involves muscle shortening as it goes
through a range of motion; usually
termed flexion
Eccentric Contraction:
Involves muscle lengthening during
movement; usually termed extension
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Examples of Concentric &
Eccentric Contractions
Moving the heel closer to
the buttocks is an example
of a concentric contraction
of the hamstring
Moving the heel away
from the buttocks is an
example of an eccentric
contraction of the
hamstring
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Plyocentric Contraction
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A hybrid contraction
The muscle performs an isotonic concentric
contraction from a stretched position
Involves a “pre-stretching” of the muscle to
initiate the Golgi tendon organ reflex
The reflex causes the muscles to contract
Plyocentric training can result in functional
strength gains beyond those that can be
achieved through strength training alone
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Plyocentric Training
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Factors Influencing
Muscle Contraction
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Factors Influencing the Force and
Power of Muscle Contractions:
1.
2.
3.
4.
5.
6.
7.
8.
The individual’s state of health
The individual’s training status
Joint angle
Muscle cross-sectional area
Speed of movement
Muscle fibre type
Age
Gender
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Joint Angle
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The type of contraction and the force required
to resist an external load change as the joint
angle changes
 The contraction type and force required
depend on whether the external force
exceeds, or is less than, the internal (applied)
force
 Static, dynamic, concentric, and eccentric
contractions may all be required
 Coordination between agonist and antagonist
muscles is required
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Joint Angle
Maximal force is produced at a joint angle that
corresponds to maximal cross-bridge interaction
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Muscle Cross-Sectional Area
Body mass is positively correlated with
strength, provided that the mass is
primarily muscle tissue or lean mass
 The larger the muscle cross-sectional
area, the more force it can generate
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Muscle Cross-Sectional Area
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Muscle Cross-Sectional Area
 The
heaviest weights
of all are lifted by
athletes in the superheavyweight
category
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Maximal and Absolute Strength
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The greater the active body mass, the greater
the maximal or absolute strength
However, individuals of a smaller and lighter
physique may possess a relatively high
strength potential when the following factors
are considered:
Intramuscular coordination
Intermuscular coordination
Anatomical structure
Muscle elasticity
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Maximal and Absolute Strength
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Maximal and absolute strength are
important to athletes who are required to
overcome the resistance of a partner or
equipment
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Relative Strength
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The performance of athletes classified
by weight, or athletes who must
overcome their own body mass,
depends on the proportion of maximal
strength to body mass
Relative Strength = Maximal Strength
Body Mass
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Relative Strength
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Gymnasts rely
heavily upon the
development of
relative strength
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Relative Strength
Recreational athletes are usually
interested in increasing active
strength and reducing body mass
 This method is also used by
overweight athletes who want to lose
fat mass
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Relative Strength
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Relative strength can also be gained
by increasing strength and stabilizing
body mass
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Relative Strength
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Young recreational athletes should strive
to develop strength in addition to
increasing active body mass
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Speed of Movement
As speed of movement increases, the
force a muscle can generate decreases
 Cross bridges are compromised since
they cannot couple and uncouple fast
enough
 Thus, there is a decreased ability to
establish and maintain a large number
of cross bridges
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Speed of Movement
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Three main components of
strength related to speed of
movement are:
1. Maximal strength
2. Power
3. Muscular endurance
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Maximal Strength
Maximal Strength:
The ability to perform maximal
voluntary muscular contractions in
order to overcome powerful external
resistances
One Repetition Maximum (1RM):
The greatest force that can be exerted
during one repetition for a given
contraction of muscles
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From Greek Mythology…
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The alertness and
great strength of
Hercules, the hero of
Greek mythology,
allowed him to perform
extraordinary deeds
 The name Hercules
suggests a human
being of giant stature
and great physical
strength
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Maximal Strength
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Greater absolute strength is necessary
for activities such as weightlifting and
field events in track & field
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Power
Power:
The ability to overcome external
resistance by developing a high rate of
muscular contraction; also known as
‘speed-strength’
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Power
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Important for
performance in
activities that
require mastering
quick movements
Includes sprinting,
speed-skating,
jumping, throwing,
rowing, etc.
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Muscular Endurance
Muscular Endurance:
The ability to resist fatigue in strength
performance of longer duration; also
known as ‘strength endurance’
 Muscular endurance determines
performance capacity in events that
occur over longer periods of time,
such as rowing, swimming, and crosscountry skiing
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Muscular Endurance
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Muscular endurance is important in acyclic
events that involve strength and endurance,
including gymnastics, wrestling, boxing, and
downhill skiing
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The Relationship Between Maximal
Strength and Power
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Common misconception that
increases in maximal strength lead to
slowed muscle performance
In fact,
•
The more internal force that can be
generated to overcome external resistance,
the more movement acceleration increases
•
The higher the external resistance to be
overcome, the more important the maximal
strength for power performance
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The Relationship Between Maximal
Strength and Power
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Fast-twitch muscle fibres
increase in diameter in
response to high-resistance
training
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The Relationship Between Maximal
Strength and Power
Development of maximal strength through
hypertrophy of myofibrils
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The Relationship Between Maximal
Strength and Power
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Improved intra-muscular
coordination results in a
progressive increase in the
number of fast motor units
that can be mobilized
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The Relationship Between Maximal
Strength and Power
Development of maximal strength through
increased intra-muscular coordination
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The Relationship Between Maximal
Strength and Power
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Therefore, maximal strength
training can be beneficial to
the development of power
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The Relationship Between Maximal
Strength and Power
Development of maximal strength through
hypertrophy and increased intra-muscular
coordination
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The Relationship Between Maximal
Strength and Muscular Endurance
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The number of repetitions that can
be performed against a highresistance is dependent on maximal
strength
That is, the greater an athlete’s
maximal strength, the greater the
muscular endurance at a particular
load (as a percentage of 1RM)
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The Relationship Between Maximal
Strength and Muscular Endurance
Resistance
Level
100%
95%
90%
85%
80%
Repetition
Maximum
1
2-3
5-6
7-8
10-12 12-16
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75%
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Issues Related to the Relationship
Between Strength and Endurance
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Vigorous cardiovascular
training can lead to an
associated decrease in the
diameter of fast-twitch muscle
fibres
Thus, increased endurance
can be associated with
decreased muscle strength as
a result of a corresponding
decrease in muscle volume
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Issues Related to the Relationship
Between Strength and Endurance
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Repetitive maximal strength training
decreases endurance, but increases
strength
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Issues Related to the Relationship
Between Strength and Endurance
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A Nordic event skier competing in ski
jumping and cross-country skiing must
combine training for maximal strength as
well as muscular endurance
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Issues Related to the Relationship
Between Strength and Endurance
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Relatively high levels of both strength and
endurance can be achieved either by training
for strength and endurance in separate
training sessions, or in combination
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Muscle Fibre Type
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1.
2.
3.
The greater the fast-twitch fibre
content of a muscle…
The greater the force output;
The greater the overall speed of
contraction; and
The greater the fatigability will be
when the muscle has been maximally
activated
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Muscle Fibre Type
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The greater the slow-twitch fibre
content of a muscle…
1. The lower the force-producing
capacity
2. The slower the contraction speed
3. The greater the endurance
characteristics of the muscle
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Age
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Aging affects muscle force output
There is a loss of fast-twitch fibres
associated with aging
May occur as a result of apoptosis
May occur as a result of disuse
‘Sarcopenia’ is the medical term that
describes muscle loss
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Age
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Diminished strength and balance is
associated with muscle loss
This may lead to falls and bone fractures
Falls and fractures are a major cause of
age-related disabilities
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Gender
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The absolute force and power
capacity of women is often less than
that of men
However, there is not much
difference between males and
females when force and power data
are normalized to selected
anatomical variables
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Gender
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The differences
between males
and females is
mainly due to
the difference
that exists in
muscle volume
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