Chapter 7 - Biomechanics Flashcards
what does biomechanics examine?
the internal and external forces acting on the human body and the effects produced by these forces
what does biomechanics aid in?
technique analysis and the development of innovative equipment designs
where does the knowledge for biomechanics come from?
from sports medicine, athletic therapy, physical therapy, kinesiology and biomechanical engineering
Exchange of energy forces
biomechanics
quantitative analyses
- involves measurement of variables that are thought to optimize or maximize performance
give 3 examples of quantitative analyses
1) pattern of forces using a force platform
2) sequence of muscle activity using electromyography (EMG)
3) 3D movements of each body segment using high speed cinematography
qualitative analyses
- involves obtaining information, visually or auditorily to assess performance
what 4 things does qualitative analyses require?
1) a framework within which skilled performance can be observed
2) a set of principles with which movement can be analyzed
3) a checklist to use when identifying errors
4) techniques to use for error detection and correction
kinematics study of motion
the study of time and pace factors of a body in motion
what are the 4 variables used to describe motion?
time, displacement, velocity and acceleration
linear
straight line
angular
around an axis
time
temporal characteristics of a performance, either of the total skill or its phases
displacement
length and direction of the path an athlete or object takes from start to finish
angular displacement
direction of, and smallest angular change between the rotating bodys initial and final position
velocity
displacement per unit of time
angular velocity
angular displacement per unit of time
acceleration
rate of change of velocity
angular acceleration
angular velocity per unit of time
kinetics study of forces
focuses on the various forces that are associated with a movement
internal forces
generated by muscles pulling via their tendons on bones, and to bone-on-bone forces exerted across joint surfaces
external forces
acting from without, such as the force of gravity or the force from any body contact with the ground, environment, sport equipment or opponent
scalar quantities
have only magnitude (time)
give 3 examples of scalar quantities
speed, work, power
vector quantities
have magnitude and direction (force) displacement, velocity, momentum, lift
Straight line segments with one end defined as the tail and the arrow tip defined as the head
vectors
Levers
simple machines that augment the amount of work done by an applied force
fulcrum
a rigid body (i.e., long bone) that rotates about a fixed point (i.e., joint) called a fulcrum (F)
true or false: acting on the lever is a resistive force (R, i.e., weight of a limb segment) and applied force (AF, i.e., muscle contraction)
true
what are the 3 classes of levers?
a) first class
b) second class
c) third class
give an example of a first class lever
teeter-totter
give an example of a second class lever
wheelbarrow
give an example of a third class lever
barbaque tongs
factors affecting the moment of force
a balanced teeter-totter
newtons 1st law of motion
the law of inertia
the 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
newtons 2nd law of motion
the law of acceleration
the law of 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 3rd law of motion
the law of reaction
the law of reaction
- for every action there is an equal and opposite reaction
- the 2 acting forces are equal in magnitude, but opposite in direction
give an example of the law of reaction (newtons 3rd law of motion)
the sprinter exerts a force on to the blocks and simultaneously the blocks exert an equal force back onto the sprinter
what is the action and what is the reaction in this example of newtons 3rd law?: the tires on a car push on the road and the road pushes on the tires
action: the tires on a car push on the road
reaction: the road pushes on the tires
what is the action and what is the reaction in this example of newtons 3rd law?: while swimming, you push the water backwards and the water pushes you forward
action: while swimming you push the water backwards
reaction: the water pushes you forward
what is the action and what is the reaction in this example of newtons 3rd law?: a rocket pushes out exhaust and the exhaust pushes the rocket forward
action: a rocket pushes out exhaust
Reaction: the exhaust pushes the rocket forward
why are the models of human motion developed?
because the total movement capacity of all the body structures is to complex to accurately analyze
why is the total movement capacity of all the body structures too complex to accurately analyze? (3 reasons)
1) anatomical difference in people related to race, age, gender, health and lifestyle
2) the body is susceptible to deformation and multi-segmental so that one segment affects the others during movement
3) sport skills occur in 3D often encountering all 3 planes and axis
what are the 3 human body models?
1) particle model
2) stick figure model
3) rigid segment model
particle model
used when the object of interest (the human body or an object) is airborne after being thrown, struck or kicked the body itself (i.e., jumping, diving, tumbling)
stick figure model
used when the object is in contact with its environment and generally gross motor skills in 2D (i.e., sprint starts, running, non rotational dive)
rigid segment model
used for more sophisticated quantitative analyses (3D) especially in multi-plane motions
what 2 things are required for rigid segment model?
camera and 3D analysis
what is the first preliminary step for analyzing human motion?
identify the system to be studied, which is to separate the object of interest from its surroundings
what is the second preliminary step for analyzing human motion?
identify the frame of reference in which the movement takes place
what is the third preliminary step for analyzing human motion?
identify the type of motion that is occurring, the body planes in which movement takes place (sagittal, frontal or transverse and
identify the axes of rotation about which rotational motion occurs (sagittal, frontal, or vertical)
what are the 3 types o motion?
linear, general and angular
motion
when all parts of the body move the same distance in the same direction at the same time
linear motion (AKA translation)
refers to movement of the body as a unit without individual segment parts of the body moving relative to one another
rectilinear motion
occurs when movement follows a straight line
curvilinear motion
occurs when the movement path is curved
angular motion (rotation)
occurs when a body moves along a circular path, through the same angle in the same direction and at the same time
what is the point about which movement occurs?
the axis of rotation
all joints are what type of motions?
angular motions
general motion
a combination of linear and angular motion
what does general motion include?
most athletic and many everyday activities
causes of motion
the only cause of motion of the human body is the application of an external force
force
any action, a push or pull, which tends to cause an object to change its state of motion by experiencing an acceleration
constant velocity
occurs when an object is not accelerating
linear motion
is caused by forces which act through a body’s centre of mass
angular motion
caused by forces that do not go through the centre of mass
centre of mass
located at the balance point of a body; a point found in or about a body where the mass could be concentrated
where is the centre of mass generally?
generally 15cm (approx. 6inches) above the symphysis pubis, or approx. 55% of standing height in females and 57% in males
does the centre of mass have to be inside the body?
no
mass
a measure of inertia a constant what object is made up of
what is mass measured in?
kilograms
weight
measure of the force of gravity
what is weight measured in?
newtons
what makes the weight vary?
varies directly with the magnitude of the acceleration due to gravity (9.8m/s2)
Weight = _____ x ______
mass x gravity
Projectile Motion
any airborne object is a projectile, including the human body
parabolic path
the path that the centre of mass of a projectile follows
what is the parabolic path followed determined as?
determined only as a function of the projectiles takeoff velocity
what are the objectives of the projectile motion (what do you want the object to do)?
height - max vertical distance
range - max horizontal distance
accuracy
what is the optimum trajectory for distance?
35 degrees
what is the first principle?
stability
stability increases when there is…?
- a lower centre of gravity
- an increase in the base of support
- the line of gravity is close to the centre of the base of support
- mass increases
what is principle #2?
maximum force
how is maximum force achieved
by the use of all the joints that can be applied simultaneously
more joints = more ______ = more _______
more joints = more muscles = more force
what is the third principle?
maximum velocity
how is maximum velocity achieved?
when the joints are sequences from largest to smallest
larger slower joints start the movement, faster smaller joints contribute once the preceding joint reaches peak velocity and slow down
what is principle #4?
Impulse
the greater the applied impulse the greater the _______
the greater the applied impulse the greater the change in velocity
when does force absorption occur?
when momentum must be dissipated over time or distance (requires application of an impulse)
what is the fifth principle?
linear motion
movement usually occurs in the direction opposite that of the _______ force
movement usually occurs in the direction opposite that of the applied force
what is principle #6?
Angular Motion
how is angular motion produced
angular motion is produced by the application of a force acting at some distance from an axis, that is, by a torque
what is the seventh principle?
angular momentum
angular momentum is _____ when an athlete or object is free in the air (i.e., constant after takeoff)
angular momentum is constant when an athlete or object is free in the air (i.e., constant after takeoff)
