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
Experimental methods for the determination of segmental moment of inertia?
Cadavers pendulum method, object suspended and oscillated, time period of one complete oscillation is recorded
Inertia = (WhT^2) / 4pi^2
W = weight h = distance from suspension point to CG T = time period of one complete cycle
Overall what is inertia determined by?
Mass of body
Distribution of mass about the centre of gravity
Why is it more difficult to rotate in a straight position than when tucked?
Because more mass is distributed further away from the axis of rotation so larger moment of inertia
Equation for angular momentum?
Angular momentum (kg.m^2.s^-1 = moment of inertia (kg.m^2) x angular velocity (radians.s^-1)
In the air is total angular momentum constant?
Yes
If the angular momentum of one part of the body is decreased another part must increase to conserve total angular momentum
During running the relative ankle angle at ground strike is typically?
90 degrees
Equation for average loading rate (N.s^-1)?
Peak impact force (N) / time of occurrence (s)
How to calculate total body centre of gravity using a reaction board?
Determine the body weight of subject
Reset the readings on the scales so it isn’t weighing the board
Lay the person on board
Use the equation xW = 2(R2 - R1) rearranged to x = (2(R2-R1)) / W
W = subject weight (mass x 9.81)
R1 = scale reading for the board (will be 0 if you zero the scale) but if just given the force do the weight x 9.81
R2 = scale reading for the board + subject (mass x 9.81)
2 has come from the board being 2 metres long
x will give you height in which centre of gravity is, can then find percentage of total height
Calculation of total body centre of gravity using the segmental approach?
Head - vertex (very top of head) to chin-neck intersect Trunk - suprasternal notch to hip (lower down than you think) Upper arm - shoulder to elbow Forearm - elbow to wrist Hand - wrist to knuckle Thigh - hip to knee Calf - knee to ankle Foot - heel to tip of longest toe
(ALL JOINTS NEED TO BE MARKED IN CENTRE ESPECIALLY THE KNEE)
Mark all of these on diagram and connect them with straight lines
Measure the length of each segment and determine the location of the centre of gravity using the percentages that will be given (provide calculations to 4 d.p) and mark it
Create OX and an OY axis on the diagram
Measure the distance in mm from each centre of gravity to each axis
Create a results table which for each segment has the ratio weight (multiplied by 2 for any body segment which is double), distance to OY in mm, moments about OY, distance to OX in mm, moments about OX
Moments are calculated via ratio weight multiplied by distance to the axis
At the bottom write down the sums of moments for OY and OX
Write down the relationship Sum of moments = moment of the resultant, (sum of (use symbol E) migxi = MgX
mig = ratio weight and Mg = 1
Then write down X coordinate and Y coordinate, then mark on diagram where it is (from origin go the amount of mm down it then combine them)
ALL CALCULATIONS TO 4DP
How to calculate whole body moment of inertia?
Head - vertex (very top of head) to chin-neck intersect Trunk - suprasternal notch to hip (lower down than you think) Upper arm - shoulder to elbow Forearm - elbow to wrist Hand - wrist to knuckle Thigh - hip to knee Calf - knee to ankle Foot - heel to tip of longest toe
(ALL JOINTS NEED TO BE MARKED IN CENTRE ESPECIALLY THE KNEE)
Mark all of these on diagram and connect them with straight lines
Measure the length of each segment and determine the location of the centre of gravity using the percentages that will be given (provide calculations to 3 d.p) and mark it
Measure each centre of gravities distance to the centre of gravity given in mm
Determine a scaling factor, so to convert mm values to metres just have to divide the mm by how many mm the metre scaling factor is
Create a table which has the headings Segment, Moment of inertia about segment centre of gravity (kg.m^2) (will be given), Mass ratio (will be given), Segment mass in kg (multiply ratio by mass of subject), measured distance from segment centre of gravity to whole body centre of gravity (mm), Real distance from segment centre of gravity to whole body centre of. gravity, md^2, Icg = Is + md^2, number of segments, moment of inertia about body centre of gravity (kg.m^2)]
So calculations are md^2 = mass x distance^2
Then find Icg by adding the MI about segment centre of gravity, then multiply by the amount of segments, then sum them all up to have answer moment of inertia in kg.m^2
Mcneil, 2005?
Footwear biomechanical level, structure, function, motion, mechanical aspects, biological systems
Kleppner, 1973?
Angular kinematics, rotational motion, absence of forces
Angular kinetics, rotational motion, regard to forces
Clinghan, 2008?
Profit, shoe companies
Clarke, 1983?
Motion control shoes, reduction, rear foot motion, ankle inversion injuries, anterior knee pain, plantar fasciitis
Medial posting, dual density
Barret, 1985?
Affects athlete wellbeing
Figures 1?
Figure 1: Rearfoot motion graph, y 5 to -10 rearfoot angle, x time
Upside down bell curve
Average 8-10 degrees
Label maximum
Figure 2?
Right leg going outwards then inwards labelled supination
Label rearfoot angle
Right leg going inwards then outwards
Label rearfoot angle
Figure 3?
4 pieces of bone, top left, top right, middle, bottom
Talocrural joint = top and left of middle bone
Subtalar = bottom of middle bone
Description of figures 1 and 2?
Rearfoot motion
heel stance, = supination, =inversion plantar flexion adduction
Midstance, = pronation, = eversion, dorsi flexion, abduction
Toe off = propulsion
Description of figure 3?
Foot and ankle complex
Subtalar = frontal + transverse movement, dissipation of momentum, hardness for propulsion
Talocrural, dorsiflexion + plantar flexion, hinge joint
Hrelijac (2000)?
Lower extremity, biomechanical and anthrpometric, kinetic + kinematic, force plate, 4m.s^-1, filming
Looked at people with overuse injuries and no injuries
Found lower velocity in pronation in overuse injuries
= motion control detrimental
Luz (2017)?
Patellofemoral pain, kinematic data, 3D system
Greater rearfoot eversion = patellofemoral pain
Changing it can reduce symptoms
Barton - eversion helped using kinematics in motion not static
Conclusion for main paragraph 1?
Hrejilac (2000), small sample of 20, retrospective, grouped injuries
Luz (2017), more recent, but cross sectional, only kinematic data, rehabilitation rather than prevention
Introduction main point 2?
Prospective better than retrospective
Rice (2013)?
Ankle inversion risk, 145 injury free male recruits
Plantar pressure, kinematic variables
No association, peak eversion or eversion range
Was associated with narrower bimalleolar breadth width
Willems 2005?
223 PE students, lower leg alignment + 3D kinematics and plantar pressure obtained
6-18 months after injuries collected
Injury = maximum time in pronation, so footwear is beneficial
Mini conclusion for main paragraph 2?
Both studies valid large and prospective
Talk about individualism
Acronym?
Mcneil Kicked Cafu Causing Bednter Horror Like Robin Williams
Mcneil (2005) Klepnner (1973) Clinghan (2008) Clarke (1983) Barret (1985) Hrelijac (2000) Luz (2017) (BARTON, 2011) Rice (2013) Willems (2005) (ALTMAN, 2016)
Data obtained?
Hrejliac (2000) - biomechanical and anthrpometric, kinetic + kinematic, force plate, 4m.s^-1, fining
Luz (2017) - kinematic data, 3D system
Rice (2013) - Plantar pressure, kinematic variables
Willems (2005) - lower leg alignment + 3D kinematics and plantar pressure obtained Hrejliac (2000) - biomechanical and anthrpometric, kinetic + kinematic, force plate, 4m.s^-1, fining
Luz (2017) - kinematic data, 3D system
Rice (2013) - Plantar pressure, kinematic variables
Willems (2005) - lower leg alignment + 3D kinematics and plantar pressure obtained
Briefly describe how a diver can increase and decrease their whole body moment of inertia during a dive, and suggest how this relates to their performance.
By pulling the legs and arms closer to the point of rotation, the moment of inertia decreases and the angular velocity increases, allowing them to perform more manoeuvres
faster rotation
increase the moment of inertia again to decrease the angular speed, by straightening out to enter the water
Which kinematic change did Liebermann et al. (2010) observe when comparing those who run barefoot with a fore-foot strike with those who run shod with a rear-foot strike?
a more plantar-flexed ankle at landing in barefoot runners
What does medial flare do?
Reduces pronation, hence eversion
What does a lateral flare do?
Increases pronation, hence eversion
In Nunns et al. (2013), which footstrike modality was associated with the highest values for forefoot loading?
toe runner
Barton (2011), fits in after Luz?
Normally static measured, they looked at kinematics in motion focusing on pronation
26 individuals with PFP showed improvement with greater rear foot eversion over 12 weeks
Study to go after Willems from Altman (2016)?
Evidence may suggest we go barefoot
First prospective study barefoot vs shod
201 (107 barefoot and 94 shod) adult runners.
Injuries and mileage was logged monthly using a custom, webbased database program
More calf injuries found in barefoot, more hip and knee in shod
similar injury rates.
Talk about individualism
Briefly describe the relevance of the centre of gravity location to a swimming sprint start from a block.
Athletes mass = centre of gravity = force acting downwards
Shortest distance between force and the line of the force x
The further forward the centre of gravity results in a larger distance hence a larger moment so they can go faster
Nunns et al (2013) reported that approximately what percentage of habitually shod runners adopted a heel strike style when asked to run barefoot?
77%
Tangenital velocity (linear)?
angular velocity x distance
