Biomechanics final deck Flashcards
Whats a minute?
1/60 of a degree
How to convert degrees into radians?
divide by 57.3
What’s angular speed?
Angular distance / time
What’s angular velocity?
w = (change in angular position) / (change in time)
Units are radians/s
What’s angular acceleration?
Change in angular velocity / change in time
Units are radians/s^2
What’s a relative angle?
Between 2 different segments
Knee, ankle
What’s an absolute angle?
Angle defined relative to a line in space
Describes orientation of segment in space
Thigh, foot
When given 3 points with coordinates how to calculate the angle behind the knee?
Cosine rule: a^2 = (b^2 +c^2) - (2bc cos angle)
But first have to determine the 3 lengths via Pythagoras theorem
Rearrange to find the angle
= cos angle = (b^2 + c^2 - a^2) / (2bc)
Or you can use right angled triangles find the angles next to the one you want then do 180 - the 2 angles you have found using SOH CAH TOA
Why does heel lift reduce potential for achilles tendon strain?
There is reduced ankle angle and no change in knee angle
Results in reduced ankle dorsi flexion so less likely to strain
2 types of athletic injury?
Acute - are associated with a traumatic event such as those from a hard tackle or from falling
Chronic (overuse) - from result from repetitive action such as long distance running or repaired throwing
What are intrinsic factors (within the body)?
Age Sex Previous injury Aerobic fitness Muscle strength Reaction time Anatomical alignment Postural stability
What are extrinsic factors (outside the body)?
Footwear
Surface
Competition level
What is an eccentric force?
Force whose line of action does not pass through the centre of gravity
Always causes a rotational movement and therefore a moment
Can also cause translation
What is a couple?
2 equal and opposite parallel forces
No translation
But rotation occurs about the centre of gravity
What is the moment of a couple?
turning effect that a couple produces
amount of rotation depends on:
Magnitude of one of the forces (the forces are equal)
perpendicular distance between lines of action
Moment (M) = F1 . x (perpendicular distance)
What is a moment influenced by?
Length of the moment arm
Magnitude of the force
Direction of the force
What is the resultant moment?
Sum of all moments about a defined point
Have to take into account negative direction
Will let you know the direction of rotation
What is equilibrium?
When sum of all forces is 0
So if told this can find out unknowns in a moments question
What is the centre of gravity?
Point about which mass is equally distributed - an imaginary theoretical point
3 methods for the calculation of total body centre of gravity?
Suspension:
A cardboard cut-out of the body shape is suspended from a point. In equilibrium, a vertical line is drawn on the cardboard, through the suspension point. This line passes through the centre of gravity. The procedure is repeated using a second suspension point. The point where the two lines intersect is the centre of gravity of the body.
Reaction Board:
A reaction board is supported by a block of wood at one end and a set of scales at the other. A subject lies on the reaction board. Since the board and subject are in equilibrium, the sum of the moments is zero. Knowledge of the reading of the scales and the length of the reaction board, allows calculation of the location of the centre of gravity. (calculations in lab book)
Segmentation Method:
This method uses the relationship: the sum of the moments about a point is equal to the moment of the resultant force. Mass and centre of gravity locations for each body segment are obtained from the research literature and used to calculate total body centre of gravity location. (calculations in lab book)
Determination of body segment mass and centre of mass?
Don’t Call Harrison Yellow Zebra Head
Cadaver studies:
Dempster (1955) - 8 frozen cadavers, limbs cut through appropriate joint centres, trunk divided into 3 segments
Clauser (1969) - 13 cadavers, same division, not frozen
Mathematical modelling - Hanavan (1964) and Yeadon (1990) - represented body segments as geometric shapes, truncated cones (arm, foot), elliptical spheres (head, hand), Cylinders (trunk)
Scanning techniques and regression equations for the calculation of segmental mass and centre of gravity:
Zatsiorsky (1983), Hinrichs (1975), Gamma scanning, CT scanning
What is a moment (or torque)?
The tendency of a force to cause rotation about a specific axis
M (N.m) = force (N) x distance (m)
Which of Newtons laws apply to angular motion?
Newtons 1st (angular) - a rotating object will continue to do so at constant angular momentum unless acted on by an external force
Newtons 2nd (angular):
An external moment produces an angular acceleration that is:
Proportional to the moment
In the direction of the moment
Newtons 3rd (angular): For every applied moment , there is an equal and opposite reaction moment
What is inertia?
An objects tendency to resist change in motion
Equation for inertia??
the resistance of a body to changes in angular motion = sum of all mr^2
m = mass r = distance from point of rotation to mass units = kgm^2