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CHAPTER
MUSCLES
AT WORK
6
ASSESSMENT CATEGORIES
Application
Communication
Knowledge and Understanding
Thinking
Activities in this chapter:
1
2
Types of Muscle Action 68
Review Your Key Terms
Get into Action
Factors Influencing Muscle Action 69
Review Your Key Terms
Graph the Relationships
Factors Affecting Muscle Contraction
3
Check Your Understanding 71
4
Chapter Culminating Assignment 73
CHAPTER
Muscles at Work
6.1
TYPES OF MUSCLE ACTION (Textbook pages 118-121)
1
6.1.1 Review Your Key Terms
concentric action
dynamic action
eccentric action
isokinetic action
isometric action
plyometric action
static action
6.1.2 Get into Action
A. Complete the flow chart below and provide an example for each numbered muscle action.
ER
S
Muscle Action
Dynamic
W
1. Static
2. Concentric
Order of dynamic muscle actions may vary.
1. Static: any isometric activity such as arm
wrestling, pushing against a door frame,
maintaining a hold in gymnastics
3. Eccentric
4. Isokinetic
3. Eccentric: Movement that involves muscle
lengthening such as lowering weights
during an arm curl, leg curl, bench press
AN
S
6
5. Plyometric
5. Plyometric: Box/depth jumping;
bounding exercises
2. Concentric: Movement that involves
4. Isokinetic: Weight training with
muscle shortening to overcome resistance
dynamometers such as CYBEX, Nautilus
such as arm/leg curl, bench press
B. Identify the types of muscle action represented by each of the following activities.
Activity
68
Type of Muscle Action
Activity
Type of Muscle Action
Isometric
Concentric/Eccentric
Concentric/Eccentric
Isometric
Plyometric
Concentric/Eccentric
Isokinetic
Concentric/Eccentric (Isometric if
position is held)
Kinesiology Student Workbook
CHAPTER
Muscles at Work
6.2
FACTORS INFLUENCING MUSCLE ACTION (Textbook pages 121-130)
2
6.2.1 Review Your Key Terms
absolute strength
apoptosis
maximal strength
muscular endurance
one repetition maximum (1RM)
power
relative strength
repetition maximum (RM)
sarcopenia
speed–strength
strength endurance
6.2.2 Graph the Relationships
S
If you consider Olympic lifting events as an example, definite relationships can be graphed comparing (A) body
mass and maximum load lifted and (B) body mass and relative strength. Graph the linear relationships on the
graphs below, and explain what factors account for these effects.
A
ER
450
400
350
300
250
0
52
67.5
SW
Total Load Lifted (kg)
500
There is a close connection between body mass and
strength. The greater one’s stature the greater one’s
strength – provided body mass is composed mainly
of muscle and not fat. This fact is emphasized by the
performances of weightlifters across various weight
categories. The world record in the bantamweight
division (56 kg) is greater than that in the flyweight
(52 kg) division; and in the featherweight (60 kg)
division it is higher than in the bantamweight
division. The heaviest weights of all are lifted by
athletes of the super-heavyweight category.
82.5
100
110
B
AN
Body Mass (kg)
A linear relationship exists between body mass
and relative strength – as one increases the other
decreases. The performance of athletes classified by
weight (such as weightlifters), and athletes who must
overcome their own body mass (such as jumpers,
runners, gymnasts, etc.), depends less on maximal
strength than on the proportion of maximal strength
to body mass. Relative strength can be increased by
increasing strength and stabilizing body mass or
by stabilizing maximal strength and reducing body
mass.
5.8
Relative Strength
5.4
5.0
4.6
4.2
3.8
3.4
52
67.5
82.5
100
110
Body Mass (kg)
Studying Human Movement and Health
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CHAPTER
Muscles at Work
6.2.3 Factors Affecting Muscle Action
A. List the main factors that influence muscle contraction and force output in humans.
1 Joint angle
4 Muscle fibre type
2 Muscle cross-sectional area
3 Speed of movement
5 Age
6 Sex
B. Expand your knowledge by conducting research on one of the factors you listed above. Discuss how and why
the selected factors influence muscle contraction.
Answers will vary.
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AN
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6
C.Minor-league hockey teams can see a 45-kg difference between players, especially players 11 to 14 years old.
Discuss the advantages and disadvantages of organizing minor hockey teams by weight categories instead of
simply by age. This question can be debated as a class or completed on your own.
Answers will vary. Reduction of injuries....
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Kinesiology Student Workbook
CHAPTER
Muscles at Work
Name: ______________________________________
CHECK YOUR UNDERSTANDING
3
1. Which of the following statements regarding static
muscle actions is false:
A) Maximal static action can occur in sports such as
gymnastics and wrestling.
B) Most sport activities require low to submaximal static
action.
C) Maximal static action is very common in most sports.
D)Flexing the arm against the resistance of a fixed bar is an
example of static contraction.
E) None of the above.
Answer: C
3. Which of the following is not a factor that affects a
muscle’s force and power output:
A) muscle length
B) joint angle
C) age
D)sex
E) none of the above
AN
Answer: A
Fill in the blanks for the following statements using words
from the word bank below. Place the corresponding letter
from the word bank in the blank spaces provided.
1. Dynamic contraction occurs whenever the internal
force generated by the muscle contraction results in
movement.
2. In isokinetic contraction, the neuromuscular system
can work at a constant speed during each phase of
movement against a preset high resistance.
3. The main components of strength are maximal strength,
power, and muscular endurance.
4. The ability of an athlete to resist fatigue in strength
performances of longer duration is known as muscular
endurance.
SW
Answer: D
Fill in the Blanks
ER
2. Which of the following statements regarding dynamic
muscle action is false:
A) It can include both concentric and eccentric actions.
B) It occurs when the external force is smaller than the
internal force generated by the athlete.
C) It is very common in all types of sports events.
D)It may occur without any visible change in muscle
length.
E) None of the above.
D)All of the above.
E) None of the above.
Answer: E
S
Multiple Choice
Date: _______________________________________
4. Which of the following statements regarding power is
true:
A) It is often referred to as speed–strength.
B) It is desirable in sporting events such as the high jump.
C) It determines the speed of movement execution.
D)All of the above.
E) A and B only.
5. During maximal responses, the greater the FT fibre
content of a muscle, the greater the force output, the
greater the overall speed of contraction, and the lower
the resistance to fatigue.
Word Bank
a. concentric e. isometric
i. power
b. dynamic
f. lower
j. relative strength
c. greater
g. maximal strength
k. stamina
d. isokinetic
h. muscular endurance l. static
Answer: D
True or False
5. Which of the following statements regarding the
relationship between maximal strength and power is
false:
A) The higher the external resistance to be overcome,
the more important maximal strength is for power
performance.
B) The greater the proportion of maximal strength
mobilized to perform the movement, the slower the
movement occurs.
C) The greater the maximal strength, the higher the
movement acceleration.
Indicate whether each statement is true (T) or false (F). If
the statement is false, provide the correct answer.
1.Isometric contraction occurs against a load that is
beyond the capability of the muscle(s) to move.
Answer: true
2.During a concentric contraction, extension usually
occurs.
Answer: false (Correct: flexion)
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3.The importance of maximal strength for an athletic
performance decreases as the resistance that must be
overcome in competition is reduced and as the period of
competition decreases.
5.The process of preprogrammed death of muscle cells is
called sarcopenia.
Answer: false (Correct: apoptosis)
Answer: true; false (Correct: increases)
4.Strength training and increases in maximal strength lead
to slowed muscle performance.
Answer: false (Correct: do not lead to)
Think and Link
1.Using a leg curl to provide examples, explain the differences between concentric and eccentric contractions.
W
ER
S
A concentric contraction is one in which the muscle shortens as it goes through the range of motion;
this is usually termed flexion. An eccentric contraction is one in which the muscle lengthens during the
movement, usually termed extension. During a leg curl, bringing the heels towards the buttocks (i.e.,
flexion of the hamstrings) is a concentric contraction. The movement of the heels away from the buttocks
area (i.e., extension of hamstrings) is an eccentric contraction.
AN
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2.Explain the figure below, and describe the relationship between FT muscle fibre hypertrophy and strength training.
Development of Strength Capacity
6
The figure illustrates the development of maximal
strength through muscle hypertrophy and
increased intra-muscular coordination using
short-term maximal resistance training. FT
fibres respond very effectively to high-resistance
training, which generates an increase in diameter
of the contractile elements (myofibrils) of the
fibres. Furthermore, this type of training results
in a progressive increase in the number of fast
motor units that can be mobilized. This results in
improved intra-muscle coordination.
Strength
Capacity
Initial Value
1st Cycle
2nd Cycle
Strength Training
Time
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Kinesiology Student Workbook
CHAPTER
Muscles at Work
Name: __________________________________________________________
Date: _______________________________
CHAPTER CULMINATING ASSIGNMENT
4
Case Study: An Absolute and Relative Comparison
Pia, Michelle, Marco, and Paul decide to have a weightlifting competition on the bench press using a 70-kg barbell.
Use the following information to determine and then compare their absolute (1RM) and relative muscle strength
(kg for kg). Use information in Table 6.1 on page 127 to aid in your calculations.
No. of Repetitions
1RM or Absolute
Strength (kg)
Relative Strength
(kg)
Pia
54
1
70
1.30
Michelle
78
3
74
0.95
Marco
85
12
88
1.03
Paul
100
16
93
0.93
ER
Sample answer for Pia:
S
Athlete’s Weight
(kg)
Athlete
1RM = Load (kg) / [Achieved resistance level (% from Table 6.1) / 100]
SW
Absolute strength = 70 / (100 / 100)
= 70 kg
Relative Strength = Maximal strength (kg) / Body mass (kg)
AN
Relative strength = 70 / 54
= 1.30 kg
Define absolute strength. Who has the greatest absolute strength?
Absolute strength is a measure of strength independent of a person’s body mass – the ability to perform maximal voluntary
muscular contractions in order to overcome powerful external resistance. It is the greatest force an individual can exert for a given
contraction of muscles or the greatest load that individual can lift in one attempt. In this case, Paul possesses the greatest absolute
strength.
Define relative strength. Who has the greatest relative strength?
Relative strength – also known as pound-for-pound or kilogram-for-kilogram strength – is a measure of strength that depends
on a person’s body mass, and is calculated by dividing maximal strength by body mass. In this case, Pia has the greatest relative
strength.
Describe two ways to increase relative strength.
Relative strength can be increased by stabilizing maximal strength and reducing body mass, which may be the strategy used by
recreational and overweight athletes. It is of little use to competitive athletes, however, because a reduction of body mass is often
linked with loss of muscle mass and therefore with a decrease in maximal and relative strength.
Another way to increase relative strength is to increase strength and stabilize body mass. As maximal strength is not only
dependent upon muscle diameter, but also upon intramuscle coordination, this variation is often quite promising, provided that
the correct and relevant training methods are chosen.
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CHAPTER
Muscles at Work
Discuss the relationship between maximal strength and endurance among the athletes.
The number of repetitions against high resistance is dependent on the maximal strength of the athlete. See example on textbook
page 127.
W
ER
S
The maximal feasible number of repetitions of a particular load is referred to as the repetition maximum (RM). If the RM of an
exercise is 2-3, it can be deduced that an athlete can resist a force corresponding to approximately 95 percent of maximal strength
capacity. If the athlete is able to perform maximally 7-8 repetitions with a particular weight, then this weight approximates 85
percent of maximal strength capacity.
Therefore, it is not always necessary that you work against maximal resistance (which may be very dangerous in most cases) in
order to calculate your maximal strength capacity for a given exercise. Determining an athlete’s maximal number of repetitions
against submaximal resistance will produce an accurate assessment of maximal strength. However, as the number of repetitions
increases (or as the level of resistance decreases), the RM becomes a less accurate criterion of maximal strength.
It is a commonly held belief that the development of strength hinders and even impairs the development of endurance, and
vice versa. The validity of this notion depends upon the type of training and event in question. Vigorous training for running long
distances leads to an increase in cardiorespiratory fitness (increased aerobic power). However, the simultaneous decrease in
the diameter of the fast twitch muscle fibres causes a corresponding decrease in muscle volume. These processes, then, result in
increased endurance and decreased muscle strength.
Conversely, repetitive maximal strength training decreases endurance but increases strength. Thus, the training of a weightlifter
or shot-putter is geared towards the development of maximal strength and power; endurance is hardly improved. However, unless
a specific sports event requires the possession of a maximal level of endurance or strength, training should achieve a balance
between strength and endurance.
AN
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Kinesiology Student Workbook