WEEK 9 Flashcards
(28 cards)
define ground reaction force
measures the overall loading on the body and subsequently how these forces impact the movement of the system
list the 4 force measurements
1) conductor sensors
2) strain gauges
3) spring
4) balance boards
define force platforms ( a way of measuring ground reaction force)
compromises of four transducers or strain gauges and a rigid aluminium top plate
define piezoelectric force platforms ( measurement of ground reaction force)
def= quartz crystals cut into discs perpendicular to sensitive axes
what are the advantages (x3) and disadvantages (x2) of the piezoelectric force platforms
advantages:
- large range
- highly linear
- good frequency response
disadvantages:
- exhibit draft
- expensive
define strain gauge ( measurement of ground reaction force)
sensors compromised of tri axial “whetstone bridges”
- mass is in the middles of the bridge which causes change in resistance when accelerated
- change in resistance when measured
what are the advantages ( x5) and disadvantage (x1) of strain gauges
adv:
- large range
- good linearity
- reasonable frequency response
- no drift
- reasonable cost
dis:
- size
what are the 3 elements we can measure using force plates
1) ground reaction forces
- resultant= magnitude and angle
2) centre of pressure
3) moments of x, y and z axes
describe the ground reaction forces during walking gait (x5)
100% force= force vector is peaking
- down the bottom= different sections of the gait
- when there is no force= swing or walking phase of the gait
- first peak= heel contact with the ground
- second peak= pushing off the ground
what is the vertical force in different landing tasks (gait, running, football mark and gymnastics)
gait= 1.3 x body weight
running= 3-4 x body weight
football mark= 5-8 x body weight
gymnastics somersault= 12 x body weight
describe the centre of pressure
tracing the focal point of force
it is used to look at the way of pressure shifting during activities
define strike index
where the centre of gravity begins in relation to the long axis of the foot
describe a pressure measurement ( x3)
- force per unit over which the force acts
- enables the effect of forces and/or the distribution to be studied
- typically floor based or insole technology
describe force and axis of rotation
force line of action through centre of mass or axis of rotation
define torque and identify the equation
the angular equivalent of linear force (the cause of angular motion )
force x moment arm (units= newton metres)
define moment arm and what are the two directions of torque
def= perpendicular distance from the forces line of action to the axis of rotation
direction =
- clockwise NEGATIVE
-anticlockwise POSITIVE
torque example: “why do rowers pull at the end of the oar handle”
to increase the perpendicular distance from the forces line of action to the axis of rotation (forces moment arm). this increases torque, the angular force of action
define muscle torques
muscles produce torques in the body
- apply force (pull/contract)
- cross joints or joint
- have a moment arm
these torques = joint motion
define a concentric muscle torque
produced through concentric activation of the muscle
define eccentric muscle torque
produced through eccentric activation of the muscle
describe strength training and torques on bicep curls
- the moment arm changes through range of motion
- muscles ability to create force changes through range of motion
define resultant torque and what are the 2 ways it can go
the sum of torques produced by the muscles and masses around the joint
counter clockwise
clockwise
define mechanical advantage and its equation
the ratio of force moment arm to the resistive moment arm
MA= moment arm (force) divided by moment arm (resistance)
what are the two advantages of mechanical advantage
1) less force required to move heavy objects (mechanical advantage is more than 1)
2) increased displacement at the end point (when the mechanical advantage is less than 1)
