Download LEVERS Classification of levers LEVERS

SECTION A –
UNIT 1
LEVERS
7) Figures A.74 a to c shows an elite sprinter completing a full running stride.
a) Analyse the action of the hip joint from the strike position of the left leg to the completion of a full running stride. 3 marks
b) Identify the main agonist muscles responsible for these movement patterns in figures a and b only.
2 marks
c) At the completion of the full stride focus on the left foot plant, identify the bones that form the ankle joint, the joint action and the main agonist responsible for this movement pattern.
4 marks
d) Figure c shows the right knee in a recovery position. Identify the joint type, main agonist muscle group, its antagonist muscle group and the type of muscle contraction occurring at this joint. 4 marks
e) Explain the term ‘body plane’.
2 marks
figure 15 - sprint - a full stride
figure A.74 – sprint – a full stride
f) In what plane and around which axis does the sprint leg action occur? 2 marks
figure a
figure
b
figure
c
8) Differentiate and give examples of concentric, static and eccentric work.
LEVERS
6 marks
figure A.75 - forces at origin and insertion
figure A.75 – forces at origin and insertion
The term internal forces describes the forces acting (figure A.75) when a muscle pulls
on its origin O and insertion I. The force on the origin H is equal in size but opposite in
direction to the force on the insertion U. This changes the shape of the person.
Levers
A lever is a means of applying force at a distance from the source of the force and has
a fulcrum (pivot), effort and load. In the human body, usually a joint and the attached
limbs or bones act as a lever. Force is applied as effort by a muscle or group of muscles.
The load is the force applied to the surroundings by the lever.
O
H
U
I
Classification of levers
Class 1 lever
This is a see-saw lever with the fulcrum in between the effort and the load. It is found rarely in the body, for example the triceps
/ elbow / forearm lever (see figure A.76), or the atlas / neck muscles used in the nodding movement.
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APPLIED EXERCISE PHYSIOLOGY
Class 2 lever
figure A.76 – elbow / triceps lever
This is a wheelbarrow lever where the load is bigger than the effort,
and the fulcrum is at one end of the lever with the load in between
the effort and the fulcrum. This is found rarely in the body, the main
example being the achilles tendon / calf muscles (gastrocnemeus /
soleus) and ankle joint lever (see figure A.78, page 70). This is used
in most running or walking movements with the fulcrum underneath
the ball of the foot as it drives the body forward.
a class 1 lever
fulcrum
(pivot)
Class 3 lever
This class of lever again has the fulcrum at one end of the lever
arm, with the effort in between the load and the fulcrum. It has a
mechanical disadvantage, the effort is bigger than the load and is the
most common system found in the body. For example the elbow /
biceps / forearm lever (see figure A.77), or the knee / quadriceps /
tibia – fibula systems (see figure A.79, page 70).
effort
load
fulcrum
(pivot)
effort
load
figure A.77 – the elbow and forearm lever
a class 3 lever
effort
fulcrum (pivot)
load
effort
fulcrum (pivot)
load
Classification of levers 69
SECTION A –
UNIT 1
ANALYSIS OF MOVEMENT
figure A.78 – ankle / calf lever
figure A.79 – knee / tibia / quadriceps lever
a class 2 lever
effort
effort
a class 3 lever
effort
effort
fulcrum
(pivot)
fulcrum
(pivot)
load
fulcrum
(pivot)
load
load
fulcrum
(pivot)
load
Effects of the length of lever
figure A.80 – the length of a lever arm
The length of the lever or resistance arm of the lever (d in figure A.80) affects
the load able to be exerted by the lever, and the speed at which the hand can
move. The longer the lever d, the smaller the value of the load for a given biceps
strength and value of the effort arm (distance between effort and pivot). The
longer the lever arm d, the faster the load can be applied (as the limb moves
through its range, for a longer limb, the hand would move further in the same
time).
effort
This means that the hand of a thrower with long arms will be moving faster than
the hand of a thrower with short arms if each is turning (rotating) at the same
speed.
The shorter the effort arm the less load can be exerted. The shorter the load
(resistance) arm of a person the bigger the load can be. This is why successful
weightlifters tend to have short arms.
x
load
fulcrum (pivot)
d
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APPLIED EXERCISE PHYSIOLOGY
Practice questions
1) Sketch the lever system which would represent the action of the biceps muscle in flexing the arm. Show on your diagram
the resistance arm of the lever. 3 marks
2) In figure A.81 of a jumper taking off, name, sketch and label the lever system
operating at knee B during this action.
3 marks
figure A.81 - long jumper taking off
figure A.81 – long jumper taking off
3) In softball, what order (class) of lever is shown in the hitting action in figure
A.82?
State one disadvantage and one advantage of reducing the bat length for a
beginner.
3 marks
B
B
figure A.82 - softball bat
figure A.82 – softball bat
fulcrum
(pivot)
bat
4) Name, sketch and label the lever system which is operating at the ankle of
leg C when doing the sprint set action illustrated in figure A.83. 3 marks
weight
figure
A.83 - a sprint start
figure A.83 – a sprint
start
effort
C
figure A.84 - a press-up
C
figure A.84 - a press-up
A
A
figure A.84 – a press-up
5) a) Figure A.84 shows an elbow joint A of a person performing an exercise.
Draw a simplified sketch to show the lever system, indicating the various forces operating.
4 marks
b) On your diagram draw and label the effort and resistance arm.
3 marks
A
A
6) During physical activity the performer uses a combination of levers to produce movement. Explain why the length of the
lever will affect performance. 3 marks
Practice questions 71