1. Muscles at Work
Chapter 4
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2. Objectives
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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3. Types of Muscle Contractions
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4. Types of Muscle Contraction
Forms and types of muscle contraction
Static
Dynamic
Isometric
Isotonic
Auxotonic
Isokinetic
Plyocentric
Concentric
Eccentric
Concentric
Eccentric
(overcoming,
accommodating)
(resistive)
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5. Types of Muscle Contraction
Forms and types of muscle contraction
Static
Dynamic
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6. Types of Muscle Contraction
Forms and types of muscle contraction
Static
Isometric
Concentric
Eccentric
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7. Types of Muscle Contraction
Forms and types of muscle contraction
Dynamic
Isotonic
Auxotonic
Isokinetic
Plyocentric
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8. Types of Muscle Contraction
Dynamic
Isotonic
Auxotonic
Isokinetic
Plyocentric
Concentric
Eccentric
(overcoming,
accommodating)
(resistive)
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9. Types of Muscle Contraction
Concentric
Eccentric
Isometric
Static
Isotonic
Auxotonic
Isokinetic
Plyocentric
(overcoming,
accommodating)
(resistive)
Forms and types of muscle contraction
Dynamic
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10. 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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11. 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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12. Activities Requiring Maximal Static Muscle Tension
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13. Static Contraction
Most sports require low to sub-maximal static contraction
Examples of sports that require this type of contraction include sail-boarding, alpine skiing, and shooting events
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14. Activities Requiring Sub-Maximal Static Muscle Tension
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15. 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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16. 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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17. Pushing against a stable wall is an example of an isometric contraction
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18. An isometric contraction occurs during an arm wrestling match when opponents generate equal forces
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19. 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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20. Auxotonic Contraction
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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21. Auxotonic Contraction
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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22. 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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23. Isotonic Contraction
Lowering a heavy weight at a slow and constant speed is an example of an isotonic contraction
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24. Isokinetic Contraction
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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25. Isokinetic Contraction
Examples of dynamometers that allow for isokinetic contraction include:
CYBEX
KINCOM
LIDO
HydraGym
Nautilus
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26. 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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27. 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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28. Plyocentric Contraction
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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29. Plyocentric Training
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30. Factors Influencing Muscle Contraction
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31. Factors Influencing the Force and Power of Muscle Contractions:
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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32. Joint Angle
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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33. Joint Angle
Maximal force is produced at a joint angle that corresponds to maximal cross-bridge interaction
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34. 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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35. Muscle Cross-Sectional Area
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36. Muscle Cross-Sectional Area
The heaviest weights of all are lifted by athletes in the super-heavyweight category
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37. Maximal and Absolute Strength
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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38. Maximal and Absolute Strength
Maximal and absolute strength are important to athletes who are required to overcome the resistance of a partner or equipment
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39. Relative Strength
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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40. Relative Strength
Gymnasts rely heavily upon the development of relative strength
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41. 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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42. Relative Strength
Relative strength can also be gained by increasing strength and stabilizing body mass
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43. Relative Strength
Young recreational athletes should strive to develop strength in addition to increasing active body mass
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44. 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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45. Speed of Movement
Three main components of strength related to speed of movement are:
Maximal strength
Power
Muscular endurance
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46. 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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47. From Greek Mythology…
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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48. Maximal Strength
Greater absolute strength is necessary for activities such as weightlifting and field events in track & field
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49. 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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50. Power
Important for performance in activities that require mastering quick movements
Includes sprinting, speed-skating, jumping, throwing, rowing, etc.
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51. 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 cross-country skiing
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52. Muscular Endurance
Muscular endurance is important in acyclic events that involve strength and endurance, including gymnastics, wrestling, boxing, and downhill skiing
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53. The Relationship Between Maximal Strength and Power
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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54. The Relationship Between Maximal Strength and Power
Fast-twitch muscle fibres increase in diameter in response to high-resistance training
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55. The Relationship Between Maximal Strength and Power
Development of maximal strength through hypertrophy of myofibrils
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56. The Relationship Between Maximal Strength and Power
Improved intra-muscular coordination results in a progressive increase in the number of fast motor units that can be mobilized
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57. The Relationship Between Maximal Strength and Power
Development of maximal strength through increased intra-muscular coordination
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58. The Relationship Between Maximal Strength and Power
Therefore, maximal strength training can be beneficial to the development of power
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59. The Relationship Between Maximal Strength and Power
Development of maximal strength through hypertrophy and increased intra-muscular coordination
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60. The Relationship Between Maximal Strength and Muscular Endurance
The number of repetitions that can be performed against a high-resistance 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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61. The Relationship Between Maximal Strength and Muscular Endurance
Resistance Level
100%
95%
90%
85%
80%
75%
Repetition Maximum 1
2-3
5-6
7-8
10-12
12-16
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62. Issues Related to the Relationship Between Strength and Endurance
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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63. Issues Related to the Relationship Between Strength and Endurance
Repetitive maximal strength training decreases endurance, but increases strength
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64. Issues Related to the Relationship Between Strength and Endurance
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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65. Issues Related to the Relationship Between Strength and Endurance
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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66. Muscle Fibre Type
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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67. Muscle Fibre Type
The greater the slow-twitch fibre content of a muscle…
The lower the force-producing capacity
The slower the contraction speed
The greater the endurance characteristics of the muscle
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68. Age 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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69. Age 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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70. Gender
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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71. Gender
The differences between males and females is mainly due to the difference that exists in muscle volume
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