Biomechanics (Midterm 1) Flashcards
acceleration
the rate of change of velocity, ecpressed in metres per second per second (m/s/s or m/s2)
angular motion
a form of motion in which all parts of an object do not experience the same displacement
base of support (BOS)
the area of contract between an object and its surroundings where reaction forces can be generated
center of mass (COM)
the sum of the mass where it equals zero
centre of pressure
the point on a plane surface at which the resultant pressure on the surgace may be taken to act
displacement
a ventor quantity representing in magnitide and direction the idfference in position of two points, usually measured in metres
electromyography (EMG)
the measurement of electrical activity in muscle fibers
force
a mechanical interaction between an object and its surroundings. ususally measured in Newtons (N)
force platfrom
an instrument to measure the reaction forces in three dimensions and moments about those three aces
free body diagram (FBD) -
a graphic-analysos technique that defines a system and all of its surrounding forces
kinematics
the description of motion of a body in terms of displacement, velocity and acceleration, without reference to the forces causing the motion
kinetics
the description of motion of a body in terms of the forces causing the motion
linear motion
a form of motion in which all parts of an object move in one straight line
moment of force
th erotary effect of force; torque. usually measured in Newton/metres (Nm)
position
the location of an object relative to soem reference
postural control
the maintenance of balance
qualitative analysis
the description of the type or kind of movement
quantitative analysis
the description of the quantity of how much movement
scalar
a variable that is that is defined by magnitude only
segment
a predefined protion of a whole object
vector
a quantity that conveys both magnitude and direction
velocity
the rate of change in position with respect to time. velocity is usually measured in metres per second (m/s)
velosity calculation
change in position / change in time
acceleration
change in velocity / change in time
isometric contraction
the muscle is contracting but there is no movement
concentric contraction
muscle is shortening
eccentric contraction
muscle is lengthening and contracting at the same time
peak-to-peak amplitude
the change between peak (highest value) and trough (lowest value, which can be negative)
frequency
is the number of occurrences of a repeating event per unit in time. usually meausred in hertz (Hz) and represented in cycles / second
analog-to-digital converters
device that converts alaog signals into digital signals
waveform
describes the shape of the graph or signal of any varying quantiy against time
conversion factor
change in weight / change in voltage
(maybe 283.75)
isotonic contraction
any contraction of a muscle against a constant force
- concentric
eccentric
burst % if foot contact
duration of particular burst/ contact duration
% of MVC
burst magnitude / MVC x 100
law of acceleration calculation
F = m x a
law of acceleration
the law that force is the product of an objects mass and acceleration
law of action-reaction
law stating that for every action there is an equal and opposite reaction
moment of force
the product of a force and itsperpendicular distance to a point causing rotaiton about that point
ground reaction force (GRF)
reaction force provided by the horizontal support surface on an object subjected to gravitational forces
zeroing off
to the reference of gravity
zeroing-on
to the reference of bodyweight
normalization
divide force by body weight to make it so we can measure everyone on an equal playing field
difference between walking speeds
- timing of everything is different
- force magnitude is higher when walking faster
- greater peak definition with walking faster
electrography
provides information about muscle activity
motor unit
a combination of efforent nerve and all muscle fibers it activates
monopolar
1 electrode and 1 neutral site
bipolar
2 electrodes and 1 neutral site
- can measure APs crossing the electrodes
electrode types
- surface
- fine wire
- needle
amplifiers
used to increase EMG signals to permit recording
gain factor
the multiple by which the signal is amplified (500x, 1000x)
issues with incorrect signals
too high - cuts off the top and bottom of signal
too low - system cant be recorded
influences on EMG signals
bloodflow, muscle length, muscle depth, noise ( motion, frequency)
reduce noise by…
reference to zero
shaving/clean skin
short cables
cross talk
activation of other muscle (use fine wire electrodes to prevent)
frequency
muscle activation - 10-350 Hz
motion artifacts (noise) 2-5Hz
electrode placement
middle portion
active muscle
avoid tendon
avoid motor point
parallel to muscle fibers
distance as small as possible
nyguist minimum limit
2 x highest frequency
EMG nyguist minimum limit
700Hz
typical min samping frequency
1000Hz
remove bias
centers signal around 0
remove bias equation
EMG signal - average quiet time
full wave rectification
shows fatigue and frequency content
shows signals in the positive in order to show shape
linear envelope
applies a low-pass filter to reduce the noise oef the EMG as well as smooth out the data
- this is where you can find the area under the slope
integrated EMG
represents the signals as as clear bursts of activity
- this is where you add the slopes together to find the sum of muscle force
types of thresholds
- manual muscle test (isolating a muscle with resistance)
- maximum voluntary contraction (hold muscle at optimal angle)
- amplitude threshold
- time threshold
criteria for muscle bursts
amplitude threshold
timing threshold ( lasts longer than 10-100ms)
peak-to-peak amplitude
individual action potentials during reflec tests
normalization of EMG
Fm x dFm = Fwt x dFwt
clinical use of EMG
nerve conduction velocity/tests
- latency
nerve conduction studies (NCS)
evalutate the function of the motor and sensory nerves
- easy way to rule out nerve issues
normal values for conduction velocity in the arm
50-70m/s
noraml values for conduction velocity in the leg
40-60m/s
H-reflexes
tests for
- peripheral neuropathy
- Guilian -barce syndrom
- upper motor neuron dysfunction
fatigue
fatigue is indicated by shift to lower frequencies
plot frequency/magnitude
muscle force equation
EMG = force^3 + force ^2 + force - b
muscle function
produce movement
maintian posture and position
stabilize joints
muscle roles
prime vs assistent mover
agonists and antagonists
stabilizers and neutralizers
method to identify muscle function
- identify phase of movement to analyze
- identify specific segments that are being moved and the movement, posture and stabilizations involved
- identify muscles used in the movement, posture and stabilization
- determine each muscle role
moment calculation
M = force x distance
strain
a measurement of length
stress
= force/area
coplanar
multiple forces working in the same plane
colinear
in the same line of action/line of application
vector summation
when they are colinear and coplanar, they can be added together
rate of loading
impact peak - initial force / time it took
rate of unloading
from the active peak to toe off over time
axis and planes
y axis - sagital; medio-lateral axis
x axis transverse vertical axis
z axis - frontal plane anterior - posterior
lower limb angle
= 90 + tan -1 (ankle x - knee x / knee y - ankle y)
convertion factor
rise (change in weight)/ run (change in voltage)
(converts to N)
burst duration percentage
burst duration / contact duration x 100
types of muscle movements
flexor
extensor
abductor
adductor
medial rotator
lateral rotator
