Chapter One
What is Biomechanics?
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Objective of Chapter One
• Define the terms biomechanics, statics, dynamics, kinematics, and
kinetics, and explain the ways in which they are related.
• Describe the scope of scientific inquiry addressed by
biomechanists.
•
Distinguish between qualitative and quantitative approaches for
analyzing human movement.
•
Explain how to formulate questions for qualitative analysis of
human movement.
•
Use the 11 steps identified in the chapter to solve formal
problems.
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What is biomechanics?
The term biomechanics combines the prefix bio, meaning “life,” with
the field of mechanics, which is the study of the actions of forces,
(both internal muscle forces and external forces.) In biomechanics we
analyze the mechanical aspects of living organisms.
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Sub-branches of biomechanics:
• statics: study of systems in constant motion, (including zero motion)
• dynamics: study of systems subject to acceleration
• kinematics: study of the appearance or description of motion
• kinetics: study of the actions of forces (Force can be thought of as a
push or pull acting on a body.)
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What Do We Measure/Calculate?
 Anatomical landmarks:
•
Position (displacement), velocity, acceleration, orientation (angles).
 Segment parameters
•
Size (length, diameter, etc.), mass, centre of mass, moment of inertia,
bone geometry (for muscle moment arms)
 Joint kinetics
•
Joint reaction forces, net joint moments, joint contact forces
 Muscle activity
 Material properties
• Bone, cartilage, muscle, tendon, ligament, fat, skin
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What is kinematics?
What we visually observe of a body in motion is called the kinematics
of the movement. Kinematics is the study of the size, sequencing, and
timing of movement, without regard for the forces that cause or result
from the motion. The kinematics of an exercise or a sport skill is
known, more commonly, as formMET
or235technique.
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Vicon Camera System
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What is kinetics?
Kinetics is the study of forces, including internal forces (muscle
forces) and external forces (the forces of gravity and the forces
exchanged by bat and ball).
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Finite Element Modeling
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Kinematics and Kinetics
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Anthropometry
Anthropometry: refers to the measurement of the human individual
A head-measuring tool designed for
anthropological research in the early 1910s.
Theodor Kocher was inventor of the
craniometer
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What is kinesiology
Kinesiology, also known as human kinetics, is the scientific study of
human
movement. Kinesiology addresses physiological, mechanical, and psychological
mechanisms. Applications of kinesiology to human health include: biomechanics
and orthopedics, strength & conditioning, sport psychology, rehabilitation, such as
physical and occupational therapy, as well as sport and exercise.
Kinesiology is the study of human movement.
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What is sports medicine?
Sports medicine is the study and practice of medical principles related to the
science of sports
Sports medicine is an umbrella term that encompasses both clinical
and scientific aspects of exercise and sport.
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What questions or problems
are studied by biomechanists?
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What questions are studied by biomechanists?
When not subject to gravitational force,
astronauts lose significant amounts of bone
mass. (Bone atrophies when not subjected to
forces.) Exercise, however, is known to
increase bone mass.
So what kinds of exercise should astronauts do
while in space in order to preserve as much
bone as possible?
Do your own research: What is Osteoporosis?
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her lifting weights or lifting
boxes in industry, the act of lifting
places major mechanical stress on
the low back.
What lifting kinematics (techniques)
can minimize this stress?
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Photographs showing a subject lifting a 20-kg box with the stoop technique (first
column), squat technique (second column), straddle technique (third column), and
kneeling technique (last column).
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How do toddlers learn to balance their
torsos on little legs unaccustomed to
walking?
(This question spans the fields of
biomechanics, motor learning, and
motor development.)
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Pitching can lead to stress injuries of the elbow and shoulder joints.
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Recreational runners, as well as athletes in many sports, often stretch
before a work out.
Does this actually help or hinder performance? (Increasing evidence
suggests MET
the235latter…)
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What biomechanical elements of running technique enable some
sprinters to dominate over others who are just as well trained and
have just as strong physiological attributes?
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Qualitative vs. Quantitative
 qualitative: pertaining to quality (without the
use of numbers)
For example: strong, skillful, agile, flexible, fast
 quantitative: involving numbers
For example: running speed = 5 m/s
height = 1.75 m mass = 68.2 kg
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Quantitatively, the robot missed the coffee cup by 15 cm.
Qualitatively, he malfunctioned.
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Coaches rely heavily on qualitative observations of athletes’
performances in formulating advice about technique.
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Steps in Solving Formal Quantitative Problems:
 Read the problem carefully.
 List the given information.
 Write down what quantity is to be solved for.
 Draw a diagram of the problem situation.
 Select the appropriate formula to use.
 Review the problem statement to determine if more information
can be inferred.
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 Substitute the given information into the formula.
 Solve the equation for the unknown variable.
 Do a “common sense” check of the answer.
 Box in your answer, including the correct units of measurement.
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Example 1:
Two schoolchildren race across a playground for a ball. Ahmed starts running at a
distance of 30 meters from the ball, and Walid starts running at a distance of 24
meters from the ball. If Ahmed’s average speed is 4.2 m/s and Walid’s average
speed is 4.0 m/s, which child will reach the ball first? Show how you arrived at
your answer.
Answer:
𝑡𝑖𝑚𝑒 =
𝑡𝐴ℎ𝑚𝑒𝑑 =
30𝑚
,
4.2𝑚/𝑠
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑠𝑝𝑒𝑒𝑑
𝑡𝑊𝑎𝑙𝑖𝑑 =
24𝑚
4.0𝑚/𝑠
𝑡𝐴ℎ𝑚𝑒𝑑 = 7.2 𝑠, 𝑡𝑊𝑎𝑙𝑖𝑑 = 6.0𝑠
7.2s > 6.0s , so Walid reaches the ball first.
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Example 2:
A 0.25 kg ball is kicked with a force of 50 N. What is the resulting
acceleration of the ball?
Answer:
1 𝑁 = 1 𝑘𝑔 𝑚/𝑠 2
𝐹𝑜𝑟𝑐𝑒 = 𝑚𝑎𝑠𝑠 𝑋 𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛,
𝐹 = 𝑚𝑎
𝑎 =
𝐹
𝑚
𝑚
𝑎 =
50 𝑘𝑔 2
𝑠
0.25 𝑘𝑔
𝑎 = 200 𝑚/𝑠 2
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