Download Biomechanics-2015

BIOMECHANICS
CHAPTER 15 IN TEXTBOOK
INTRODUCTION
• Biomechanics: the application of mechanical
principles in the study of living organisms.
• Bio: structure and function of living organisms
• Mechanics: analysis of the actions of forces
SUB-BRANCHES OF BIOMECHANICS
• Statics: study of systems in constant
motion, including systems at rest (zero
motion).
• Dynamics: study of systems that are subject
to acceleration.
• Kinematics: study of the description of
motion (space and time).
• Kinetics: study of the actions of forces
(“push” or “pull”) acting on systems.
SYSTEM
• A system is any structure or organization of
related structures whose state of motion is of
analytical interest.
• A system of interest should be selected
BEFORE deciding to how best to analyze
motion.
• A system could be:
• An entire human (e.g, treat the whole body as a “point”
during a jump)
• Part of human (e.g., throwing arm, knee joint when walking)
• An object the human has struck or manipulated (e.g.,
soccer ball, barbell during a clean-and-jerk)
NEWTON’S MODELS
• Sir Isaac Newton created this model in 1687.
• Known as the Three Laws of Motion
• Explain how forces work and became the basis for
modern physics and thus biomechanical aswell
1. Law of Inertia
2. Law of Acceleration
3. Law of Reaction
LAW OF INERTIA
• A body will maintain a state of rest or constant
velocity unless acted on by an external force that
changes the state.
• Therefore, a motionless object will remain motionless
unless there is a net force (not counteracted by
another force) acting on it.
• Similarly, a body travelling with a constant speed
along a straight path will continue its motion unless
acted on by a net force that alters its SPEED or
DIRECTION of motion.
• What external forces can be applied to the body
when standing still? What does it depend on?
LAW OF ACCELERATION
• Is an expression of the interrelationships among
force, mass and acceleration. F=ma (force = mass x
acceleration)
• A force applied to a body causes an acceleration
of that body of a magnitude proportional to the
force, in the direction of the force, and inversely
proportional to the body’s mass.
NEWTONS
• Force is measured in Newtons (N)
• 1N = 1 (kg) (m) / (s2)
• Gravity is a pulling force which is exerted on us by
the earth and it occurs at a rate of 9.8 m/s2
• Thus, something that is 102 grams or 0.102 kg would
have a weight of 1 N on earth. ( 0.102 x 9.8 = 1N)
• ***1000 grams = 1kg
MECHANICAL LOADS ON THE BODY
• Stress is the distribution of force within a body. Quantified
as force divided by the area over which the forces act.
• Types of stress:
• Axial- directed along the longitudinal axis of a body
• Compression- pressing of squeezing force directed axially through a
body
• Tension- pulling or stretching force directed axially through a body
• Shear- force directed parallel to a surface.
• Bending- asymmetric loading that produces tension on one
side of a body’s longitudinal axis and compression on the other
side.
• Torsion- load producing twisting of a body around its
longitudinal axis
• Combined- simultaneous action of more than one of the pure
forms of loading.
WEIGHT VS MASS
• Weight and Mass are not the same!
• Mass: Quantity of matter comprising an object.
Measured in kilograms [kg]
• Weight: amount of gravitational force exerted on
an object. Product of mass (m) and gravitational
acceleration (g) wt= mg [N].
• Since weight is a force, in addition to its
magnitude[N], its point of application and direction
must be specified.
• Direction is toward center of the earth.
• Point of application is CoG.
FORMS OF MOTION
• Linear motion (translation)
• Rectilinear (motion along a straight line)
• Curvilinear (motion along a curved line)
• Angular motion (rotation)
• Rotation around a fixed axis (circular path)
• General motion
• Combination of linear and angular motion
http://www.youtube.com/watch?v=MNDB5QU5bB
Y
ANGULAR MOTION
• Just like Mass this is the resistance to rotation/movement.
The larger the moment of inertia the larger the moment
of force required to spin or stop spinning. In other words,
the further the mass is from the axis, the greater the
moment of inertia and thus the harder it is to start or stop
spinning and vice versa.
• Figure skater pg 229. As the skater brings their arms into
the centre of their body their angular acceleration
increases because they have reduced their moment of
inertia.
• Gymnastics---following a series of rapid somersaults in
mid air the athlete straitens out their body. By opening
up they increase their moment of inertia and slow down
as they prepare to land. (i,e. the force stays the same
and there is now a larger moment of force thus the body
slows down
LAW OF REACTION
• For every action, there is an equal and opposite
reaction.
• When one body exerts a force on a second, the
second body exerts a reaction force that is equal in
magnitude and the opposite in the direction on the
first body.
Sample problem:
A 90 kg ice hockey player collides head-on with an
80 kg player. If the first player exerts a force of 450 N
on the second player, how much force is exerted by
the second player on the first?
TYPES OF FORCES
• Internal forces- e.g. muscles pulling on
bones
• External forces- e.g. gravity, contact
with ground, environment (wind), sport
equipment, opponent, etc.
SEVEN PRINCIPLES OF BIOMECHANICS
• Grouped into four categories:
•
•
•
•
Stability
Maximum effort
Linear Motion
Angular Motion
STABILITY
• “Proper stability &
balance are
essential to efficient
movement”
• Resistance to
disruption of
equilibruim
• See notes on stability
from earlier unit.
MAXIMUM EFFORT – PRINCIPLE 2
• “Production of maximum
force requires the use of all
possible joint movements
that contribute to the task’s
objective.”
• With more joints coming
into play, the more muscles
there will be to contract –
leading to greater force
being exerted.
MAX EFFORT- PRINCIPLE 3
• “Production of maximum velocity requires the use of
joints/muscles in order – from largest to smallest.”
LINEAR MOTION- PRINCIPLE 4
• “The greater the applied impulse or force, the greater
the increase in velocity.”
• The harder you hit an object, the farther it will travel.
• Impulse: product of force and the time over which the
force acts (J). The product of force (F) and time (t)
J=Ft [Nxs]
• When a vertical jump is executed, the larger the
impulse generated against the floor, the greater the
jumper’s takeoff velocity and the higher the
resulting jump.
• Impulse can be positive or negative. WHY?
LINEAR MOTION- PRINCIPLE 5
• “Movement usually occurs in the direction opposite that
of the applied force.”
• Examples: Resistance of water in swimming, pushing off
floor before jumping, etc.
• Related to Newton’s 3rd Law (Reaction)
ANGULAR MOTION- PRINCIPLE 6
• “Angular motion is
produced by the
application of a
force acting at some
distance from an
axis.”
• Angular velocity
increases closer the
object is to the axis
of rotation.
• Examples: figure
skating spinning,
diver spinning,
throwing a curve
ball.
ANGULAR MOTION- PRINCIPLE 7
• “Angular momentum is constant when an athlete or
object is free in the air (or airborne).”
SCALARS VS. VECTORS
• Scalar quantities: Quantitiy described by
magnitude ALONE.
• E.g., speed, distance, mass, length, energy,
volume, density
• Vector quantities: Quantity possessing
magnitude AND direction, and adds
according to the parallelogram law.
• E.g., force, moment of force (torque),
displacement, velocity, acceleration,
momentum.
VECTOR OPERATIONS
• Vector composition: Two of more vectors can be
ADDED to produce a single vector quanitity called
a “resultant” (adding)
• Vector Resolution: Vectors can be resolved into
their perpendicular components (subtracting)
• Vector composition and resolution can be
performed:
• Graphically: represent vectors as arrows
• Trigonometrically: Use basic trigonometric relationships
(solving right angle problems using SohCahToa)
VECTOR COMPOSITION- GRAPHICALLY
Tip to tail
Make a triangle
VECTOR OPERATIONSTRIOGOMETRICALLY
• Resolve vectors V1 and V2 into their rectangular
components and find the resultant (Vr=V1+V2)
MUSCLE FIBER ARCHITECTURE
• An important variable influencing muscle function is
the arrangement of fibers within a muscle. These
structural considerations affect the strength of
muscular contraction and the range of motion
through with a muscle group can move a body
segment.
• Two categories of muscle fiber arrangements are
termed parallel and pennate.
Parallel- the fibers are
oriented largely in parallel
with the longitudinal axis
of the muscle. (e.g.,
sartorius, rectus abdominis,
and biceps brachii)
Pennate- the fibers lie at
an angle to the muscle’s
longitudinal axis. Each
fiber in a pennate muscle
attaches to one or more
tendons, some of which
extend the entire length of
the muscle. The fibers of a
muscle may exhibit more
than one angle of pennation (angle of
attachment) to a tendon.
The tibialis posterior, rectus
femoris, and deltoid are
pennated muscles
PHYSICAL FITNESS
PART 3 OF BIOMECHANICS
PHYSICAL FITNESS
• The body’s ability to function efficiently, to enjoy
leisure time, and be healthy, and resist hypokinetic
diseases
• Consists of health related fitness and skill related
fitness
Health related
Body composition
Cardiorespiratory
capacity
Flexibility
Muscular endurance
Muscular strength
Skill related
Agility
Balance
Coordination
Power
Reaction time
Speed
BODY COMPOSITION
• Relative percentage of
muscle, fat, bone
• A person who is
physically fit has a
relatively high amount of
lean muscle mass, and
bone density
• Body fat for men 5-25%
• Body fat for women 830%
CARDIO-RESPIRATORY FITNESS
The ability of the heart,
lungs and blood vessels
to deliver oxygen, and
nutrients efficiently to
the tissues
Individuals who are
Physically fit, have
higher ventilitory
thresholds and
anaerobic thresholds
FLEXIBILITY
• Range of motion
available in a
specific joint.
• This becomes
problematic later
on in life as it limits
an individual’s
range of motion
and thus ability to
perform every day
functions.
MUSCULAR ENDURANCE
Ability of a muscle to
repeatedly exert itself
A fit person can repeat
movements over a
longer period of time
How many times?
• The ability to exert
an external force or
lift/move a heavy
object.
• Can hinder an
individual’s ability
to complete daily
chores/activities
• How much?
AGILITY
• Ability to rapidly and accurately change direction
of the entire body in space.
BALANCE
• Static Balance- ability
to maintain
equilibrium while
stationary
• Dynamic Balanceability to maintain
equilibrium while
moving
COORDINATION
• Ability to use senses with the body to perform motor
tasks smoothly and accurately
SPEED
• The ability to perform a movement in a short period
of time.
POWER
• The ability to exert a force at a fast rate
• This is the combination of muscular strength and
speed
REACTION TIME
• The time elapsed between the
stimulus/stimulation and the beginning
to the reaction to the stimulus
TRAINING
• Sir Roger Bannister became the first
person to run a mile in less than 4
minutes (1954)
• His training techniques were at the
cutting edge in that day….
• However if you were to compare them
to today’s methods they seem quite
primitive
WHAT IS TRAINING
It is a process by which the human body is made
more efficient. In physical activity, individuals seek to
improve their fitness components through training
Eg. Running longer/faster, shooting a basketball more
accurately, or lifting more weight
It is a process by which the human body is made
more efficient. In physical activity, individuals
seek to improve their fitness components through
training
Eg. Running longer/faster, shooting a basketball
more accurately, or lifting more weight
F.I.T.T
• Common training program
• Frequency: providing just enough stress for the body
to adapt to AND allowing enough tme for healing
and adaptation to occur.
• Intensity: the amount of effort that should be
invested in the training program or one session.
(measure by THR & MHR)
• Type: what type or kind of exercise you should
choose to achieve the appropriate training
response
• Time: how long you SHOULD be exercising for.
F.I.T.T
TRAINING PRINCIPLES
• Overload
• Progression
• Specificity
• Individual Differences
• Reversibility
• Diminishing Returns
TRAINING PRINCIPLES
• Overload: In order for physiological change to
occur, the human body must be subjected to
greater stresses than it is accustomed to. Applies to
aerobic and anaerobic exercise.
• Eg. Of aerobic overload?
• Eg. Of anaerobic overload?
• Progression: In order for the effect of the training to
progress, the athlete must be subjected to
progressively greater and greater overloads.
• Eg. Once you can lift 100 lbs on the bench press 12
times on your 3rd set increase the amount to 110 lbs.
TRAINING PRINCIPLES
• Specificity: Also called the S.A.I.D. principle (
Specific Adaptations to Imposed Demand). In order
for specific outcomes to occur, training exercises
must be specific to those outcomes. Thus the
training should mimic activities from the actual
sport.
• Individual Differences: Every athlete has a different
physiological and psychological makeup and thus
will have different needs when training.
• E.g. History, type of activity, fitness level, age,
gender, ability to recover from intense workouts.
• Reversibility: When training is removed, muscles will over
time lose the benefits that training brought about.
Atrophy occurs, and muscles lose size and strength. Use
it or lose it!
• Diminishing Returns: Individuals who have trained little or
not at all will experience greater results than those who
have trained for longer periods of time.
• Elite Sprinters train endlessly in hopes of decreasing their
times by hundredths of seconds while a beginner may
decrease their time by seconds
• Plateaus often occur in individuals training for long
periods of time