71 terms

# HK 263 Test 3

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Static equilibrium
a motionless state where fores and moments cancel each other.
Dynamic equilibrium
a state of motion with a balance between applied forces and internal forces.
Static
equations of equilibrium
Dynamic
equations of motion
Is there such thing as a balance score?
No, too complex to have a single score. Multifunctional skill.
Stability
resistance to disruption of equilibrium, resistance to linear and angular accelerations
Balance
ability to control equilibrium
5 factors to increase stability
increase mass, increase friction, larger BoS, lower COM
Is standing still mechanically stable or unstable?
unstable
Center of Pressure (COP)
location of ground reaction forces
Units of COP
meters
Center of Mass (COM)
the point around which a body's mass is equally balances in ALL directions
Units of COM
meters
If the COP is ahead of the COM
longer moment arm, largest moment, pushes forward, person falls back
If the COM is ahead of the COP
person moves forward, COP moves forward to keep balance
In a passive system, if the COM is pushed outside of the base of support, what happens?
it falls over
When a person initiates gait, the COM moves outside the BOS, why don't they fall?
the step to move the COM forward
Three mechanical reasons humans are unstable
COM is high, BoS is small, leg joints can lead to vertical collapse
Controller (sheep dog)
COP
Sheep
COM
neuromuscular system
combination of the nervous and muscular system
concentric contraction
muscle shortens during contractions
eccentric contraction
muscle lengthens during contractions
isometric contraction
muscle stays the same length while contracting
musculotendinous unit
muscle + tendon
Four behavioral properties of a musculotendinous unit
extensibility, elasticity, irritability, ability to develop tension/force
extensibility
ability to increase in length
elasticity
irritability
ability to respond to a stimulus
when a person initiates a forceful stretch of a muscle group immediately before contracting that muscle group
strech-shortening cycle
motor unit
a single motor neuron and all the fibers it innervates
fast twitch fiber
reaches max tension more quickly than slow twitch
slow twitch fiber
important for endurance
parallel fiber arrangement
parallel to the long axis of the muscle
pennate fiber arrangement
fibers act at an angle to the long axis of the muscle
which fiber arrangement can generate more force?
pennate fibers
which fiber arrangement has a greater range of motion?
parallel fibers
what are the four roles of assumed by muscles during movement?
agonist, antagonist, stabilizer, neutralizer
agonist
causing the movement
antagonist
opposing the movement
stabilizer
counteracts external force
neutralizer
a muscle causes an unwanted movement
active insufficiency
inability to develop tension
passive insufficiency
cannot stretch full range of motion due to tightness of stretched multi-joint muscle on opposite side
what factors affect muscular force generation
fiber type, muscle size, # of fibers, and pennation angle
what muscle length do we get optimal force?
150% resting length
what type of contraction generates optimal force?
eccentric
what kinetic quantity do we describe muscular strength
moment of force, moment, torque
do we tend to describe the strength of individual muscles or muscles groups?
muscle groups
when body temp. increases, what 5 changes occur?
increase speed of nerve conduction, muscle function, oxygen supply, and waste removal. decrease in the number of motor units needed to sustain Cx
what contraction is most effective at developing muscle size and strength?
eccentric
what contraction produces the most force?
eccentric
what contraction produces the least force?
concentric
what contraction is most likely to result in muscle strain?
eccentric
Can loss of strength be slowed and reversed?
Yes
1st degree muscle strain
<5%
2nd degree muscle strain
5-99%
3rd degree muscle strain
100% tear
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
Law of Acceleration
An applied force causes an acceleration of the body:
1.with a magnitude proportional to the force,
2.in the direction of the force, and
3.inversely proportional to the mass.
Law of Reaction
For every action, there is an equal and opposite reaction
What happens to acceleration when force increases?
it increases
What happens to acceleration when mass increases?
it decreases
what is the direction of acceleration?
the direction of the force
two major factors of force?
mass and acceleration
GRF's represent the summation of the acceleration of what?
all of the body segments, COM
What can a person do to reduce GFR on a force plate?
bend down quickly
What can a person do to increase GFR?
push upwards
when a person is standing quietly, what is the vertical force?
body weight
friction acts in what direction?
opposite to motion
what are the two types of friction?
static and kinetic