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Lecture 1: Introduction to Advanced Biomechanics
Landing Biomechanics - ACL Injuries
Anterior/posterior part of cruciate ligaments refers to the muscle attachment site on the tibia = anterior attaches to anterior side of tibia crossing backwards to
the intercondular notch of the femur
...
70% of ACL injures occur during non-contact situations e
...
landing, cutting, deceleration, changing direction
...

Risk factors in Females:
Anatomical
Smaller cross sectional area of joint
Narrower intercondular notch (in femur) = limited space for ACL to move around
Greater Q angle = angle at which the femur meets the tibia, an approximation of the angle that the quads pull on the tibia, determined between the ASIS to the
centre of patella to the tibia tuberosity
...
Greater Q angle = quads pull at a greater angle = increased
force and twisting on the knee
...
Research suggests at different times in a women’s menstrual cycle
ACL strength and the amount of pressure it can withstand may vary
...
Greater
contraction of the quads compared to the hamstrings can cause anterior displacement of the tibia (abnormal
movement of the tibiofemoral joint = increased loading on the knee
...
Trunk flexion can reduce the load on ACL and stretches the hamstrings
and gluteus maximus = increases the muscles ability to exert force = increased force production of GM and H =
increased hip extension moment, reduced knee extension moment and reduced knee valgus moment
...
If knees are
flexed, the patella shifts backwards = more vertical patella tendon = smaller force through patella tendon, more vertical force than forward force = less strain on
ACL
...
(2014)
...
Research in Sports
Medicine, 22(2), 193-212
...
The hamstrings work to prevent anterior dislocation of the tibia relative to the femur
...

Glutes - stronger glutes (mainly medius and maximus) can prevent valgus movement (knee moving inwards)

Lecture 2: Advanced Motion Analysis
3D motion analysis
Used to record position and orientation of the body in 3-dimensional space
Usually integrated with 1 or 2 force plates enabling recording of kinetic variables, ideally one force plate for each leg
Sometimes integrated with EMG to show muscle activity (the term integrated means time synchronised)
Benefits
Highly accurate and all movement captured as the cameras are permanently set in position
It is becoming easier to use with advancing technology - quicker, more accurate, less technical problems with modern systems
Drawbacks
Expensive and complex
Fixed indoors - controlled environment but less ecologically valid, too much light to be used outside - system finds it difficult to locate markers
Applications
Mainly used for research purposes:
- Performance enhancement - running, golf, cricket, baseball, rowing - mainly sports to improve technique
- Injury prevention - both mechanisms of injury and risk factors
Also used for diagnostics:
- Gait labs in hospitals
- To inform surgical procedures e
...
if a child is not walking properly, it can be used to identify which muscles are causing the problem (e
...
may be constantly
contracting) and can then perform surgery (e
...
to turn the muscle activity off)
Research Strategy
Applied focus:
- Further knowledge of human movement for performance enhancement/injury prevention
- To identify variables of interest and then measure those (e
...
come up with a rationale, identify biomechanical risk factors relating to the problem - then
measure the risk factors)
Technology led:
- Large amounts of data can be collected (joint angles, forces, moments, powers in all planes of motion) and relationships between them can be determined
- Sometimes easier to measure everything so as not to waste data and then makes sense of it e
...
to find out which variables relate to the problem
- However, this can lead to data dredging = lack of a rationale, hard to relate back to rationale due to overwhelming data
Systems
Hardwire/Active marker systems:
Linked through wires
Used to record movement in small volume that doesn’t require multiple rotations/twists
Pros - no markers are lost, all markers will be tracked
Cons - may hinder movement due to lots of wires
Passive marker systems:
Markers are not connected
Highly reflective - relies on reflection of infra-red light by reflective spherical markers
Requires more cameras - between 2 and 12 cameras (synchronised)
No
...
of markers and capture volume (bigger capture volume =
more cameras needed)
Passive marker systems are more common
How the system works
Tracks 3D coordinates of markers placed on the body
A series of LED lights surround the camera emitting infra-red light
Markers are covered in retro-reflective material
Light is reflected back to the camera exactly where it came from so the marker can be located
Each marker must be seen by at least 2 cameras in order to show distance and positon (all planes for
3D view)
Data Collection Procedures
1
...
g
...

Place cameras around chosen area - evenly spaced using tripods or wall mountings - pros and cons of each, e
...
tripods limit space in the room for movement,
may be knocked and have to redo calibration
...

Ensure dead-space is minimised (space where no movement is happening)
...

Synchronise other hardware e
...
force plate

2
...
This demonstrates the amount of error each camera is giving you
...
Static calibration - L-frame (a right angle), has 4 markers on it, is placed in the room usually on corner of force plate
2
...
Marker Sets - Label subject with markers in correct positions
Configuration of markers designed to model body or object - models the body as a series of ‘segments’
Minimum of three non-collinear (not in a line) markers required per segment
- Defines position and orientation of segment in 3D
- Two makers define a line; the third marker is required for rotations
Accuracy improved by more cameras viewing a marker, at least 2 seen by each camera, aided by appropriate spacing between markers
Determine the type of marker set to ensure quality of data and variables can be calculated:
Standard Clinical Gait Marker Set
Cluster Based Marker Set
Tried, tested, validated
Benefits
Software provided to speed up data
Can reduce skin movement artefact
processing
Small number of markers over simplifies
segments e
...
foot
Required static trials to locate anatomical points relative to
Limitations
Designed for lower extremity gait so
cluster
may not be valid for sporting
movements
Helen Hayes Marker Set - list of 29
Cleveland Clinic Marker Set - cluster of markers (3 markers)
Example
markers and their
placed in the middle of a segment which has a known
locations/positioning’s
relationship to anatomical points required for processing

Custom Marker Set
Overcome some limitations of
standard marker sets
Time consuming and requires high
knowledge of anatomy and
computer programing

Marker Placement
Ensure asymmetry - aids in automatic recognition of markers, ensures system doesn’t confuse left & right
...
Markers subjected to greater accelerations require
additional support (elastic bands)
...
Record a static trial
Assume motorbike position - knees and elbows flexed to allow the system to identify which way you are facing
Used to identify the main joint centres - ankle, knee and hip
Done by positioning markers on the lateral and medial side of joints as the camera plots the joint centre point between the two markers
The medial knee and ankle markers can be removed after the camera has identified the joint centre
5
...
Record experimental trials
Processing data
The system tries to automatically identify markers throughout the trial
Cleaning data:
- Check markers are identified in every frame
- Join broken trajectories - small breaks that are not at peaks in trajectory
...

Determines components of signal that oscillate at high (skin marker movement) and low (human movement) frequencies and discards signal above the cut-off
frequency (walking = 6Hz, running = 8-12Hz)
...

Often determined by trial and error of different cut-off frequencies and observing the effects
...
All data can be exported into excel for analysis
...
, McClay, I
...
, Richards, J
...
(2000)
...
Gait and Posture, 11, 38-45
...
, 2000
What does the paper state is the major limitation of video based motion analysis and how much error can this cause?
Soft tissue movement - tracking markers are attached to soft tissue relative to the bone - meaning as subjects so do the tracking markers
...

What is likely to affect the error identified in Q1?
Transverse plane of motion, movements in this plane are quite small
...

This was in order to determine an optimal surface tracking marker array for tracking motion of the tibia during natural cadence walking
...
e
...

How were data filtered?
The marker coordinates were zero phase lag filtered using a 4th order Butterworth digital filter set at a cut-off frequency of 6Hz
...
05)
Summarise the main differences between the 11 surface marker arrays
The surface marker arrays differed in:
- The location they were attached - lateral shank vs
...
distal
- Physical characteristics of the marker set - constrained vs
...

- The method used to attach the marker array to the segment - overwrapped vs under wrapped
What were the key results?
Location of markers when using the lateral shank marker were the only factor to effect rotational kinematics
Rotations were significantly smaller when markers were placed more distal (better when markers are more distally placed)
No significant factors identified for the medial border of tibia marker set
What was proposed as being the best marker set?
Distal lateral shell under wrapped (DLU) followed by the DTP and PTO
However even when using the best marker set (DLU), rotational deviations of ±2° about the medio-lateral and anterior-posterior axes and ±4° about the
longitudinal axis were noted in the individual subject data
What general trends are proposed in the Discussion?
Less error for lateral shank when markers were attached using under wrap and placed more distally
What recommendations are made with regards to the Cleveland Clinic marker set and the Helen Hayes marker set?
Cleveland clinic marker set - triad markers attached to a rigid shell and positioned over the mid-lateral segment being tracked
...
Also would be best to position the marker set at a distal location
...
The wand-projected marker is attached to a
rigid shell positioned over the mid-lateral segment and may also benefit from under wrap attachment and distal location
...

Even when using the best marker set, what rotational deviations were observed for individual subjects?
Larger deviations were noted during the first and last thirds of stance, smaller deviations and less variability during mid-stance
First third deviations related to inertial effects during foot contact with the ground
Mid-stance deviations associated with gastrocnemius and peroneals producing lower levels of force at this time
Last third deviations related to muscles of the shank (gastrocnemius and peroneals) generating force to propel the body forward for push off
...

To model soft tissue movement, the model must not only account for the magnitude and timing of the rotational deviation but also the direction of the
deviation
...
a for linear case
Force = mass x acceleration (Newtons second law)
↓ Angular equivalent
Στ = I
...
ms) = mass x radius of gyration2
Estimating Joint Torque
a) Acceleration diagram
b) Shank and foot segment

Fknee
τknee

τknee = internal/muscle torque
Fknee = net joint force
W = segment weight
dW = moment arm of the segment weight
GRF =ground reaction force
dGRF= moment arm of the ground reaction force
m = mass of segment
a = linear acceleration of segment
da = moment arm of the linear acceleration of segment
αs = angular acceleration of segment

dGRF

dw

αs
da

GRF

as

W

Newtons second law of motion:
Sum of the torques is equal to the rate of change of angular momentum of the
segment
τknee - W
...
dGRF = m
...
da + I
...
dw + GRF
...
a
...
α
MUS = GRAV + EXT + MDT + NET

MUS = muscle torque = τknee = torque exerted by the muscle and articular forces
GRAV = gravitational torque = W
...
dGRF = torque acting on segment due to GRF
MDT = motion dependent torque = m
...
da = torque acting on segment due to the motion of adjacent segments
NET = net joint torque = I
...
Quasi-static model
Quasi means ‘as if’ - e
...
as if it is static
Assumes that segment mass and linear and angular accelerations of segment COG are zero
This means we can take out GRAV, NET and MDT
MUS is considered equal and opposite to EXT
2
...
Inverse dynamics model
Takes into account all components of MUS
Most commonly used model and most accurate as takes into account all possible component torques
Motion analysis system automatically calculates joint torques using this method

Estimating Net joint torque
When segment mass and linear/angular accelerations of segment are small relative to EXT, more closely EXT will
approximate MUS - quasi-static model for calculating joint torque is justifiable
Quasi-static model is more accurate when joint is closer to point of application of GRF – therefore for lower limb
determination of MUS by quasi-static model most accurate for the ankle, then knee, then hip
Alexander and Vernon (1975) - in two 68kg male subjects’ landings from a 0
...
m using quasi-static model
compared to 111N
...
Shows some discrepancy between the models

Inverse Dynamics
Calculates forces and torques based on accelerations of object instead of measuring forces directly
System usually defined as a series of segments
Generally conducted in order of distal to proximal segments - starts at foot and moves up the body to shank, thigh, pelvis etc
...
Body is considered to be rigid body linked system with frictionless pin joints
2
...
Moment of inertia about an axis of each segment remains constant
In reality these are not the case but is what we assume for the purposes of inverse dynamics
2D Example
Linear acceleration broken down into horizontal (x) and vertical (y) components
Three independent equations used:
Horizontal: ΣFx = m
...
ay
Angular equivalent: ΣTcm = Icmα
Where:
- x and y = represent the horizontal and vertical directions
- a = acceleration of centre of mass
- ΣF = sum of forces in respective direction
- m = mass of segment
- Icm = moment of inertia about centre of mass
- α = angular acceleration about centre of mass
- Tcm = torque about centre of mass
Foot during swing phase of gait cycle
Mass of foot = 1
...
0096kg
...
66rad
...
35m/s2
ay = 7
...
ax
Rx = m
...
16kg x -1
...
57N

Vertical joint reaction force (Ry)
Ry and W are the forces acting in y direction
Weight is negative as pointing downwards
ΣFy = m
...
ay
Ry = m
...
16kg x 7
...
16kg x 9
...
3N

Joint torque (τankle)
To determine net joint muscle torque, all torques acting on a system must be evaluated
If COM of foot is considered the axis of rotation, three forces are acting:
- Two due to joint reaction forces (Rx and Ry) and the net ankle muscle torque itself
- Weight is also a force acting on the segment however will not cause rotation so can be discounted
Rx is pointing to the left on x-y chart because it worked out to be -1
...
07m x 1
...
07m x 20
...
0096kg
...
66rad/s2)
= -0
...
m + 1
...
m - 0
...
m
= 1
...
m
Net muscle torque at ankle is positive therefore tending to rotate the joint anticlockwise = dorsiflexion torque
- Indicates net dorsiflexion muscle torque
- Exact muscles acting cannot be determined and could be concentric or eccentric in nature
Data produced from foot segment analysis used in calculations for next segment (shank) to calculate net muscle torque at knee and so on
Analysis can be conducted for each joint at any instant in time for a movement
Generates a profile of net muscle torque for complete movement (joint net muscle torque against time)
Contributors to Joint Torque and Force
Body Tissue
Muscle/tendon
Ligaments

Joint Force
✓
✓

Skin
Blood Vessels
Nerve
Ancillary Structure (e
...
bursa)
Bone

~0
~0
~0
~0
✓ Friction between bones

Joint Torque
✓
Only at the ends of ranges of motion e
...
to prevent
hyperextension/ hyperflexion
~0
~0
~0
~0
~0

Questions
1) Consider a soccer penalty kick in which acceleration of the foot is measured as: ax = 40m/s2
Ground reaction force is measured as: GRFx = 25N
GRFy = 125N
Moment arm for both is 0
...
2kg
Moment of inertia about COM is 0
...
m2
Angular acceleration of foot is -8rad/s2
Calculate Rx, Ry, and τankle

ay = 100m/s2

ΣFx = m
...
ax
Rx = m
...
2kg x 40m/s2) - 25N
= 48N - 23N
= 23N
Positive means it is moving to the right (clockwise)
ΣFy = may
Ry + GRFy - W = m
...
ay - GRFy + W
= (1
...
2 x 9
...
772
= 6
...
α
τankle = - τRX - τRy – τGRFx - τGRFy + Icm
...
07) – (-6
...
05) – (25 x 0
...
14) + (0
...
61 – -0
...
5 – 17
...
096
= 1
...
34 – 3
...
5 – 0
...
1N
...
What is the difference in estimated joint
torque?
Quasi-static model assumes that segment mass and linear and angular accelerations of segment COG are zero
MUS (muscle torque) is equal and opposite to EXT (external torque, torque acting on segment due to GRF)

Στcm = Icmα
τankle + τRX + τRy + τGRFx + τGRFy = Icm
...
α - τRX - τRy - τGRFx - τGRFy
= 0 - 0 - 0 - (25 x 0
...
14)
= 0 - 3
...
5
= -21N
...
W
...
R
...
, Cowley, H
...
(2005)
...
Medicine and Science in Sports and Exercise, 37(6), 1003-1012
...
, 2005
What does the paper say regarding the association between sagittal plane biomechanics of the knee during landing and ACL injury?
Sagittal plane kinematics and quadriceps muscular forces do not produce abnormal ACL loads during landing and cutting
The majority of the variables were observed in the frontal plane not the sagittal plane
Peak hip and knee flexion and ankle dorsiflexion angles were greater in females in the sagittal plane
Females exhibited a greater ROM in the sagittal plane
What does the paper suggest is lacking in the previous research investigating the lower limb joint kinetics during landing?
Few studies have looked at the temporal (timing) performance differences of lower joint kinetics
...

Why might there be a link between knee joint moments and ACL injury?
Large knee extensor moments from landing are associated with anterior knee shear (anterior tibia displacement)
When this is coupled with varus-valgus knee moments it can exacerbate ACL loads
Briefly state the main aim of the study
To quantify gender differences in the frontal and sagittal plane kinematic profiles (hip, knee and ankle joint angles)
To quantify gender differences in the frontal and sagittal plane kinetic profiles (hip, knee and ankle joint moments)
To examine the temporal occurrences of the peak events of the above parameters during drop landings
Discuss the similarities and differences between the task
Similarities - Helen-Hayes marker system
Differences - Less markers, only used lower limbs
Explain what the authors mean when they refer to ‘internal joint moments’ and elaborate on what produces this moment
...

Ligaments at the end of range of motion - could resist movement
How do the authors interpret the results of the timing relationship between peak knee joint moments in the frontal and sagittal plane and peak knee valgus
angle?
The authors interpreted the timing relationships in the peak knee varus-valgus and the peak knee extension moment magnitudes to suggest that females are
more prone to higher ACL loads during the drop landing because of the greater valgus knee position combined with a low varus moment (large valgus moment)
at the same time that a high knee extensor moment is being applied to the joint
...
Loading of a muscle
...
Muscle spindles are stimulated
...
Eccentric contraction therefore relates to negative
work
...
Unloading of a muscle
...

Force and displacement occur in the same direction (resulting in positive work)
...
Eccentric phase
2
...
Concentric phase
Examples include:
1
...
Throwing - pull arm backwards for more force to throw
Mechanisms of SSC (Linthorne, 2001)
1
...
Release of elastic energy stored in the muscles and tendons during pre-stretch
...
‘Potentiation’ of muscle
...
Increase in strength of nerve impulse due to eccentric contraction
4
...

5
...
Series Elastic Component (SEC)
The elasticity within the muscle and tendon that acts in a series (in a line: tendon → muscle → tendon)
Connective tissue, but mostly located in tendons, when stretched, SEC acts as a spring; elastic energy is stored
If concentric action begins immediately after stretch, stored energy is released
If concentric muscle action does not occur immediately following the stretch or if eccentric phase is too long, stored energy dissipates as heat
2
...
Contractile Component (CC)
Actin, mysosin, cross-bridges, primary source of muscle force during concentric contractions

Neurophysiological Model:
Changes in muscle force-velocity characteristics caused by stretch – relates to
stimulating muscle spindles within the muscle
Stretch Reflex
Muscle spindle wrapped around a muscle fibre, stimulated when stretched
suddenly to contract and shorten the muscle fibre - a protective mechanism
...
to the CNS
The body’s involuntary response to an external stimulus that stretches muscle
Response is an increase in activity of agonist muscle (increasing force in that
muscle)
...
Pause between the
phases should be as short as possible for the
action to be effective
...


Physiological Event
1
...
Muscle spindles are stimulated
(Neurophysiological)
1
...
Alpha motor neurons transmit signal to
agonist (Neurophysiological)
1
...
Alpha motor neurons stimulate the
agonist
(Neurophysiological)

Results of Action
Potential energy is stored in the muscles and
connective tissue
...

Stretch inhibitors send signals to the CNS
...

Elastic energy is released from muscles and
connective tissue
...


Work
Useful product of chemical energy used
...
d
Work = force x displacement (in the direction the force is acting - If different directions = Work is negative, if the same direction = Work is positive)
Power
The rate of doing work
...
g
...
m) and ωj is joint angular velocity (rad/s)
Muscle power may be positive or negative
- If Mj and wj are both positive or both negative, Pm will be positive
- If they have opposite signs Pm will be negative
Concentric muscle action = positive work by muscles, as torque and displacement are in the same direction
Eccentric muscle action = negative work by muscles, as torque and displacement are in different directions
Muscle Power
a) Concentric action of elbow flexors - positive power, Mj and ωj are both positive
b) Concentric action of elbow extensors - positive power, Mj and ωj are both negative
c) Eccentric action of elbow flexors - negative power, Mj is positive and ωj is negative
d) Eccentric action of elbow extensors - negative power, Mj is negative, ωj is positive
Flexion Phase
Net muscle torque initially positive but becomes negative as arm becomes more flexed
Initial part results in positive power - concentric action of flexor muscle
In latter part, power is negative indicating eccentric muscle action:
- Eccentric action of elbow extensor muscles occurs to decelerate limb
- Even though power is negative, it does not mean no flexor muscle activity but indicates muscle activity is
predominantly extensor
Extension Phase
Initial part, muscle activity is concentric extensor activity, positive muscle power
In the latter part, muscle power indicates flexor concentric activity (again to decelerate limb)

Jakonsen, M
...
, Sundstrup, E
...
D
...
, Andersen, L
...
, Krustrup, P
...
(2012)
...
Human Movement Science, 31, 970-986
...
, 2012
What is proposed to cause enhancement in jumping performance as a result of strength training?
Enhanced muscle power output resulting in enhanced neuromuscular activity
Increased contractile rate of force development during jumping and isometric tests
Increased cross-sectional area of type II fibres, increased motor unit recruitment, increased motor unit firing frequency, and synchronisation
...

What equipment was used to assess jumping performance and what variables were measured? Explain how these variables were derived from the raw data
collected
...
a = a = F/m)
Acceleration = change in velocity/ time Change in velocity = acceleration/time
Rate of power development = steepest part of power line on graph
Rate of force development = steepest part of force line
What stats were performed?
All muscle output data was expressed relative to body weight
One-way analysis of variance on repeated measures - ANOVA
Newman-Keuls post-hoc test when a significant interaction was detected
Pearson’s product-moment method to test for associations between % pre-to-post changes of selected variables
What were the key results relating to the vertical jump stretch shorten cycle muscle performance?
Maximal jump height increased 17% following strength training
Strength training resulted in shortened countermovement jump take-off time - 20% reduced duration of the time from minimum vertical jump force until takeoff & reduced eccentric phase and concentric phase
Increased maximal jump height, peak downward and upward velocity of COM, rate of vertical force development, peak power production, peak hamstring rate
of EMG rise
Mean plantar flexor phase power increased 41%
Rate of power development increased 29%
Increased lower limb stiffness by 38% post strength training
Soccer training displayed increased peak quadriceps rate of EMG rise
Strength and soccer training displayed increased quadriceps muscle fibre size and lean leg mass
...


Lecture 5: Coordination
A kinematic analysis of how joints move together as a whole rather than looking at individual joints in isolation
Looking at the relationship between joints of the same limb
Movement Theories
Two theories on how movement is controlled:
1
...
Dynamical systems theorists argue:
Existence of common optimal motor patterns is a fallacy
Intra- and inter-individual variability is typically observed in motor performance (Intra- = within or inside
...

Dynamical Systems Theory
Relates to motor control and psychology - how the brain controls movement and how you learn and develop skills
Looks at movement stability in dynamic systems
Human movement is a highly intricate network of co-dependent sub systems (highly complex) - respiratory, circulatory, nervous, musculoskeletal, perceptual
Large number of interacting components - blood cells, oxygen molecules, muscle tissue, enzymes, connective tissue, bones
In biological systems, movement patterns emerge through generic processes of self-organisation
Number of degrees of freedom of the motor system is reduced through development of coordinative structures
Reduced complexity of motor system encourages development of functionally preferred coordination (your preferred way of doing something - termed an
‘attractor state’)
‘Attractor’ states support goal-directed actions
Within each attractor state, dynamics are highly ordered and stable - consistent movement patterns for specific tasks
Variation between multiple attractor states permits flexible, adaptive motor system behaviour - encourages exploration of performance contexts
Paradoxical relationship between stability & variability: explains why skilled athletes are capable of both consistency & change in motor output
Variability in movement allows performers to explore task and environmental constraints to acquire stable motor solutions
Novice = learn preferred coordination for a given skill
As you get more skilled you can adapt the skill more (exploration) to form new skills
E
...
running through a field - can adapt stride length to avoid tripping over - whereas a novice (child who recently learnt to run and is less experienced) would
struggle
Kinetic Chain
Segment linkage system through which energy and momentum are transferred sequentially
E
...
lower limb kinetic chain (hip, knee and ankle)
How you move a limb in a kinetic chain will alter movement and loading of other limbs and joints in that kinetic chain
Often unclear how body segments are coordinated to optimise energy and momentum transfer
Lack of understanding may be due to methods used by investigators to examine body-segments dynamics
Previous studies tend to describe kinetic chain in terms of peak velocities with a lack of description of temporal sequencing providing little information about
segmental interactions and energy transfer
Coordination is one way to look at the kinetic chain as a whole as well as looking at different joints in the same kinetic chain
Coordination
Relative timing of motion between body segments (Jenson et al
...
g
...
Time Series Approach (Discrete Relative Phase)
2
...
g
...
g
...
g
...
angle

Time Series Approach (Discrete Relative Phase):
Main way of assessing discrete coordination
Angle of two joints determined during movement - plot angle of joint against time
DRP between two joints is assessed by determining:
- initial start point (ts)
- timing of maximum angles of joints analysed (t1 and t2) (doesn’t matter which is t1 and which is t2)
- finish time (tf)
DRP angle = t1 - t2 x 360°
tf - ts
tf - ts is the duration of the stride (final - initial/start time)
Ranges between 0° and 360°
Mean DRP angle: degree of coupling
A degree of 0° means they are completely in phase - occur at the same time
A degree of 180° means they are completely out of phase
St Deviation of DRP angle: variability of coupling
Example:
During a running stride, initial contact takes place at 0
...
97s
...
54 and peak hip angle at 0
...

DRP = 0
...
6 x 360° = -21
...
97 - 0
...
07 ± 41
...
75 ± 20
...
67 ± 33
...
17 ± 52
...
g
...
60 ± 65
...
62 ± 42
...
g
...
Relative motion (Angle-angle diagrams)
2
...
g
...
Anderson & Sidaway (1994)
- Angle-angle diagram
- Subjects kicked a ball at a target as hard as possible
- ROM of the hip and knee greater for expert than novice
- With practice, coordination of hip flexion: knee flexion of novices became more similar to
coordination patterns of an expert
Vector Coding
The orientation of the vector between two adjacent points on an angle-angle diagram is plotted
relative to the right horizontal
...
, 2005 – compared joint coupling patterns and variability of the rearfoot and tibia during running in subjects treated with 2 types of orthotic devices
to control group
...
Used vector coding
Fig 2
...
, 2000)

Phase Diagrams
Joint angular velocity plotted as a function of joint angular displacement
Can plot two joints on the same graph, e
...
hip and knee
Calculate phase angle of one joint at any one point in time and then the phase angle of
another joint at a point in time
Relative phase angle is the difference between two joint phase angles
Phase angle (φ) is the angle between a line from the origin of the graph to the current
data point (θ, ω) and the right horizontal
...
3
Continuous Relative Phase (CRP)
Is calculated from the relative phase angle of a pair of joints on a phase diagram
Phase angle (φ) is derived from normalised phase-plane plot
Angle displacement and angular velocity are normalised between -1 and +1, where -1 =
minimum value and +1 = maximum value in each cycle or for all cycles
CRP angle is the difference between phase angles of two joints at corresponding time
intervals throughout a cycle
Mean CRP angle over a number of cycles indicates the type of relationship between
joints: In-phase (CRP = 0°) or anti-phase/out-of phase (CRP = 360°)
Standard deviation of CRP angle over a number of cycles indicates variability in
coordination
CRP and CRP variability can be plotted against normalised time to examine changes in
coordination during a cycle
Advantages - evaluates both spatial and temporal coordination between two joints
during the entire cycle
Disadvantages - requires complex calculations and normalisation procedures
- only appropriate for cyclic movements (e
...
walking, running, cycling, hopping)

Hamill et al
...
CRP(a) and CRP variability (b) - time graphs over a complete stride cycle of running
Patellofemoral pain (PFP) sufferers exhibited lower variability in CRP of lower limb joint couplings than healthy subjects

Sides, D & Wilson, C
...
Intra-limb coordinative adaptations in cycling
...

Sides & Wilson, 2012
Why might the study of isolated joints not provide an effective analysis of more complex movements?
In a kinetic chain, the motion of one segment influences the motion of an adjacent segment, meaning the study of isolated joints does not effectively capture
the complexity of the coordinated motion of components of the body
...

However there is a reduced requirement for adaptability in skills where tight task constrains are imposed or in closed kinetic chain activities (e
...
cycling) - any
variability in the system may be indicative of an inconsistent performance
Do you believe that an optimal pattern of movement exists that all individuals should aim to reproduce?
I agree to a degree that an optimal pattern of movement exists as a way to reach optimal performance
...

10 consecutive revolutions within ±2rpm of the required cadence were selected for analysis
What analysis method was used to assess coordination and why?
Coordination was analysed using continuous relative phase analysis (CRP) - due to the cyclical nature of the movement and the inclusion of temporal data, which
has been deemed to be more sensitive to changes in coordination
What joint couplings were assessed?
CRP was assessed over 2 intra-limb couplings of interest:
1
...
Hip flexion/extension - Knee flexion/extension (HK)
Propulsive phase - pushing down on the pedal; Recovery - coming back up
How was coordination variability calculated?
Calculated as the standard deviation at each time point across the 10 resolutions for each condition for each participant
Key results
For both KA and HK couplings, trained participants displayed significantly lower CRPv (variability)
than untrained participants
More in-phase motion was displayed during the propulsive phase than the recovery phase for
trained athletes
For KA coupling, higher CRPv displayed during recovery phase than propulsive = less consistent,
potentially less stable movement pattern
More KA and HK in-phase motion at higher cadences - more in-phase motion as you go faster
No significant differences found for the HK coupling
Less variability at higher cadences - suggesting the faster you go you develop a more stable and
efficient movement pattern
No significant differences in CRP or CRPv between work rate conditions for KA or HK
Based on the results of this study, when might coordination patterns be most economical?
The more stable a movement pattern, the lower the metabolic cost required to maintain the
pattern at a given level of stability
Coordination patterns at higher cadences for a fixed work rate are most economical
This is attributed to lower motor unit recruitment
What are the conclusions of the study?
Coordination variability is detrimental to cycling performance
Changes in cadence influence changes in coordination and its associated variability
What are the main limitations of the study?
Work rates investigated in this study were limited and greater ranges may be required to identify
any differences that exist
Participants used a cycle ergometer - limits ecological validity as it does not replicate the variable
environmental condition of road cycling
Limited to intra-limb coordination - future work needed to investigate inter-limb coordination

Lecture 6: Leg and Joint Stiffness
Serpell, B
...
, Sacrvell, J
...
, (2012)
...
Journal of
Sports Sciences, 30(13), 1347-1463
...
, 2012
Kinetic Chain
A series of linked body segments
Kinetic chain - transmission of forces between body segments during posture or movement (Watkins, 1999)
Movement of each joint in a kinetic chain affects movements and loading of other joints
Stiffness is a way of assessing the kinetic chain as a whole
Compensatory Movements
Restricted movement in a given joint can be compensated for by other joints in a KC
However, some movement patterns are more efficient than others - this affects muscle force and loading
Small compensatory movement alters normal loading pattern
Greater the compensatory movement the greater the loading - excessive and prolonged → overloading → injury
The concept of stiffness is based on Hookes law which states that the force required to deform an object is related to proportionality constant (spring) and the
distance that object is deformed
Often the human body or body segments are modelled as a spring
Therefore stiffness in the human body/body segments describes its ability to resist displacement once GRF or moments are applied
This requires the interaction of anatomical structures such as tendons, ligaments, muscles, cartilage and bone to resist change
A number of studies have linked lack of stiffness to ACL injury
As stiffness is dependent on the interaction of functioning skeletal muscle, connective tissue and bone any passive or static measure of stiffness maybe
considered ecologically invalid as this would neglect the role of the body on stiffness
Why increased interest in stiffness?
Stiffness has been linked with both sport performance and has been associated with some lower limb injuries
Hobara et al
...
(2008) Greater leg stiffness in power athletes than endurance trained
This is important for force transmission
Stronger muscles will increase stiffness - hence greater in trained athletes
Watsford et al
...
, 2012)
...

Lack of passive stiffness associated with ACL injury (Serpell et al
...

Joint stiffness refers to torsional stiffness of an individual joint when modelled as a spring
Vertical Stiffness
Commonly considered the ‘first’ or ‘reference’ stiffness measure from which models of leg and joint stiffness have been developed
Is a measure of resistance of the body to vertical displacement after application of GRF
Common equation used to calculate vertical stiffness:
Vertical stiffness is typically considered the quotient of maximum GRF and COM displacement
Kvert = Fmax
∆y
Kvert = vertical stiffness, Fmax = maximum GRF, ∆y = displacement of COM (vertical displacement)
What is the main difference in measuring methodology?
How COM displacement was calculated - some used a method described by McMahon & Cheng (1990) while others used a method described by Cavagna (1975)
...
g
...
g
...
Max GRF/vertical
displacement of COM
Whereas leg stiffness is a measure of stiffness of the lower limb; reliant on leg compression which can only be achieved during stance
...
g
...
, 2008), one the point of force application from
GRF (Stafilidis & Arampatzis, 2007) & the other measured perpendicular distance to the ground (Rapoport et al
...
, 2001) or the ankle (Farley et al
...
, 2003)
∆y
Leg stiffness
The measure of the resistance to change in leg length after
Quotient of GRF and change in leg length
kleg = Fmax
application of internal or external forces (Serpell et al
...
, 2003)
in joint angle
∆θ
Kvert = vertical stiffness, Kleg = leg stiffness, kjoint = joint (knee) stiffness, Fmax = max GRF, ∆L = change in leg length, T = joint moment, ∆y = displacement of COM, ∆θ
= change in joint angle (joint angle displacement)

Lecture 7: Barefoot Running
Factors Driving Barefoot Running
Evolutionary perspective – is ‘natural’ better? We have evolved running in bare feet generally, so the structure should suit it’s function, makes sense that our
feet have evolved the way it has by running barefoot, so why wear shoes?
Epidemiology of running injuries – injury incidence has remained high despite advanced shoe design (Epidemiology = how many people? How they get it injured?
Why they get injured?)
Biomechanical justification – research shows running barefoot alters our biomechanics – controversy over whether this is good or bad
Footwear Design
1980s - Increased cushioning under heel proposed to reduce high impact forces (worry over GRF during running) & made more rigid shoes to support leg more
...
Scientific questioning whether complex foot structure is hampered/ weakened by fixating into rigid shoe, evolution has
taken place primarily while being barefoot
...
, 2010)
Lieberman, D
...
, Venkadesan, M
...
A
...
(2010)
...
Nature,
463, 531-535
...
, 2010
Argument that the foot has evolved BF so should be the natural form
Millions of years of running BF will have mostly involved landing with forefoot first rather than heel resulting in disappearance of initial impact forces
Heel cushioning may have led to runners striking the floor with the heel first (impact force at ground contact = 2-3 times body weight force), causing impactrelated injuries and repetitive stress injuries such as shin splints
However doesn’t consider the direction of force and body parts that are loading during running – simplistic view
5 groups of subjects ran both barefoot and in shoes - habitually shod adults in USA, recently shod adults in Kenya, habitually barefoot adults in USA, barefoot
adolescents in Kenya, shod adolescents in Kenya
Measures - foot-strike pattern (heel/mid-foot/forefoot), impact force & loading rate (from GRF) & joint angles
...

Results - Change in foot-strike pattern and reduction in force
- Subjects who run barefoot change to forefoot strike
- Ankle more plantarflexed at ground contact when running barefoot
- Running BF and FFS reduces loading rate and peak impact force – 3x lower in barefoot runners who forefoot strike than in heel strikers wearing shoes
Conclusions - In theory, higher impact forces and loading rates results in greater injury risk
- Study suggests barefoot or minimally shod running reduces the risk of injury
Final sentence in paper:
‘Controlled prospective studies are needed to test the hypothesis that individuals who do not predominantly RFS either barefoot or in minimal footwear, as the
foot apparently evolved to do, have reduced injury rates’
Study hasn’t measured long term effects of change in loading rates on different joints
Barefoot running will reduce the likelihood of some injuries but increase the likelihood of others – may not be good for everyone
Transition to Minimally Shod Running
Removal of rigid shoe (support structure) but maintaining heel cushioning
Foot is still planted on floor with heel first (RFS)
Impact forces are still high:
- Land with knees extended and legs closely aligned with lumbar vertebral column
- Whole body in rigid configuration
- Initial bounce of system on floor is dissipated in internal pressures of ankle, knee, hip, and lumbar intervertebral joints
- Cushioning of shoe is first mechanism to alleviate these pressures
Foot-ankle complex will attempt to absorb some of the excessive impact forces:
Foot is stopped from slapping on floor by ankle dorsiflexors:
- Muscles are stretched (ankle dorsiflexors (front of leg) are eccentrically contracted) in controlling planting of foot - acts as shock absorbing springs, slows the
foot down when planting on the floor
- On hard surfaces this mechanism can be overloaded, resulting in shin splints
Foot pronates as it is planted on floor:
- Initiates an unlocking of the arch of the foot allowing it to partly collapse - helps absorb impact forces
- Typical action if feet have sufficient strength and not too much flexibility
This mechanism is often addressed by wedging of the foot at the medial side of shoe:
- To prevent excessive rolling of the foot inwards
- Danger is that this mechanism is cancelled out by excessive compensation or footwear that is too rigid and eliminates its shock absorption
- Believed to lead to weakening of foot muscles and slackening of foot ligaments
If we change from running in rigid shoes to minimal shoes our feet may not be able to take over full control of this unlocking mechanism – relying on the foot to
control motion when used to the shoe doing this
Many problems have been reported that are believed to be a direct consequence of running with heel strike and are impact related:
- E
...
micro-fractures at heel, shin splints, pressure induced overloading of knee, hip & lumbar joints

Transition to Barefoot Running
Changing running technique/training/footwear will likely load muscles, joints and tendons beyond their usual functional range
Gradually loading structures beyond the range they are used to will allow them to adapt, however going from years of shoes straight into minimal shoes or
barefoot will likely cause injury
Transition should therefore be done gradually:
e
...
reduce rigid shoe and heel cushioning, wear minimalist shoes, walking barefoot and increase speed, practice FFS in shoes with a shorter stride length,
increase time/distance running BF, start on softer surfaces
...

People may underestimate time required to transition successfully to barefoot running
Removing rigid shoe and cushioning removes initial shock absorption by shoe and absorption of impact forces - entirely down to musculoskeletal structures
Initial heel strike impact force is very high and is transferred from heel bones through ankle towards knee, hip and lower back
Sensorimotor system will realise damaging effects of those high impact forces
Individuals adapt towards midfoot or forefoot landing – automatic response, results in disappearance of impact force associated with heel landing
This adaptation usually happens quickly although varies between individuals
Barefoot footstrike
Forefoot strike = flatter foot, greater plantarflexion and knee flexion
Distribute impact force over greater area than heel alone – force spread across the base of the foot to reduce
pressure on parts of the foot (mainly heel), cushioning impact
Figure 1 – GRFs,
a) Barefoot RFS – greater initial force – steeper initial slope
b) Shod RFS – less steep due to shoe cushioning
c) Barefoot FFS – less steep initial force, but still reaches the same peak force (~2
...

Greater PF torque (τankle) required when barefoot – increasing the loading of calf muscle and Achilles tendon
Knees flex at landing – absorption of impact energy now done by muscle-tendon structures
Quadriceps are used to eccentric loading – occurred during heel landing
Calf muscles are not used to eccentric loading – can cause extensive micro damage leading to muscle soreness
...
Can cause stress fractures of tibia and lower back pain
FFS = have to flex knee more and plantarflex more = reduced stride length
...
k2 = mass x radius of gyration
Performance Enhancement
Findings still unclear
Barefoot running associated with improved running economy – reduction in mass, mechanical alterations of the lower limbs (elastic compliance from the foot,
greater elastic energy storage and release)
Lighter shoes may be more economical than barefoot
Injury Prevention (Tam et al
...
75million lawsuit bought in 2012 by a customer who claimed they used deceptive marketing messages, making claims about the benefit of
the shoe that could not be supported by science, lack of evidence
...
Strengthen muscles in feet and lower legs
2
...
Stimulate neural function important for balance and agility
4
...
Allow foot and body to move naturally
Evidence linking mechanics to injury
No evidence that proves or disproves benefits of SH or BF running or that links mechanics of BF running to reduced injury risk – more evidence in next 5-10 years
Strong evidence shows impact forces & loading rates are reduced when barefoot, but remains to be proven that this leads to lower injury rates
Long term prospective studies required – follow group of people over a long period of time to see injury rates etc
...

For some, barefoot running will become the norm; for others, it will remain a training technique
Must recognise that the transition is a skill which involves significant change – must allow time to fully adapt to different loading stresses associated with
running BF, a long term investment
Continuing normal training but barefoot will likely cause injury
Biomechanical Recommendations (Vanrenterghem, 2013)
1
...

2
...
If calf muscles are overloaded, option of using cushioning capacity of shoe
...
If changing to minimal shoes, individual’s structure of feet and foot placement strategy will dictate whether feet are capable of acting as internal shock
absorber
...
When choosing barefoot footwear to resolve heel-striking related injuries, this could replace them with forefoot-landing related injuries - lack of evidence to
support effectiveness of such intervention
...
E
...
What we can learn about running from barefoot running: An evolutionary medical perspective
...

(Lieberman, 2012)
Lieberman’s evolutionary perspective of barefoot running
Barefoot running appears to be favoured as compared to the modern running shoe
In his opinion barefoot running is as natural barefoot walking and is therefore inappropriate to be considered as a dangerous ‘fad’ to be avoided without good
reason
...

This hypothesis was supported by three given consequences of wearing shoes in relation to injury:
1
...
Shoes encourage a different running form (one not arrived at from years of natural selection and adaptation)
3
...

It was also suggested that shoes are counterproductive in that they treat symptoms, such as heel pain, where pain could actually be an adaption to prevent
running in a way that causes injury
...

However, now, years after the transition to walking and running in shoes proprioceptive adaptations of the plantar surface of the foot may have been prevented
or reduced by shoes
The perspective that the foot is not designed effectively to suit its function may also be due to the need for additional cushioning, protection, support and
motion control when running and hence the need for the invention of the modern shoe
...

What are the main differences in vertical GRF (vGRF) between rear foot strikers (RFS) and front foot strikers (FFS)?
RFS landings = a marked increase in peak vGRF during initial contact with the ground, causing a spike in a GRF plotted graph
...
5-2
...

Whereas RFS running with modern shoes has been found to decrease impact force by 10% - cushioning of the shoe
In BF FFS runners, there is no impact peak generated but a smooth transition of vGRF across the foot causing a smooth curve in a vGRF time graph
...

What are the main differences in stride rate and stride length between barefoot and shod runners?
Stride rates vary enormously between runners, barefoot or shod
...


Few studies on non-elite barefoot runners show that they tend to take a higher frequency of steps (175-182 per minute) than shod runners
...
Stride length has been highly under researched
...
, 2009) which can be injury preventive
...

Also improved proprioception - as the foot adapts to the running style by increasing the number of nerve endings making you feel more grounded
...
Little research into this at present
Background
Five disability groups: 1
...
Amputee
3
...
Cerebral palsy
5
...
g
...
Anatomical extent – site of amputation or degree of visual impairment
2
...
g
...
g
...
Carbon fibre shank – very light
2
...
Soft silicon liner, which covers the stump – provides pressure redistribution, skin compatibility, tear strength and elasticity
Altered design enables artificial limb to exhibit high strength and stiffness, combined with low mass and efficient energy storage
Development in prosthetics generally directed towards:
1
...
Reducing energy expenditure – store and release energy
3
...
Reducing loads transferred to intact leg and vertebral column
Ultimate goal is to resume a full and active lifestyle
(Gutfleisch, 2003) When constructing an artificial limb, the main criteria are:
1
...
Power, flexibility and skin resistance (e
...
skin graft status) of residual limb
3
...
Amputee’s living environment
Compensatory Movements
Compensatory mechanisms develop in residual joints and intact limb:
Asymmetry reported in studies of amputee biomechanics:
- Walking and running - amputees try to maintain prosthetic limb in an upright position to ensure stability at the knee (Sanderson & Martin, 1997), force goes
straight down the knee, reluctance to flex knee is an issue to start with but improves with rehabilitation and training
- Jumping - reluctance to flex knee of prosthetic limb under loading (Strike & Diss, 2005) due to reduced strength
Amputees experience greater joint degeneration in intact limb compared to residual limb and able-bodied participants
- Amputees had a 65
...
, 2001)
- Up to 71% of unilateral lower-limb amputees have reported pain in intact limb and/or lower back (Nolan et al
...
(2008) & Weyand et al
...
t = m
...
Inertial and deformation advantages? – Prosthetic limb slighter & at end of leg = reduced moment of inertia
2
...

- As distance increases double amputees have the advantage
Running Time Analysis
Difficult to argue an advantage for single amputee athletes over able-bodied athlete (‘normal’ leg will always be the limiting factor) – same cannot be said for
double amputee athletes
Analysing 100m split times of a 400m race reveals that able-bodied athletes follow similar pattern:
- Accelerating in first 100m, maintaining speed for second 100m and losing speed over remainder of the race (Fig 1)
Differentials of time taken to run first and second 200m of a 400m race illustrate able-bodied athletes are slower in second half of the race – build-up of lactic
acid in athletes muscles – metabolic cost
Fig 2
...
k2 – blades have low resistance to angular motion
Able to generate fast angular velocity of legs
Prosthetic blades may allow for more efficient running placing less demand on the athlete
Over 400 m, Pistorius uses 30 % less oxygen than able-bodied competitors (James, 2012)
Detailed analysis of Pistorius revealed:
1
...
Lower joint moments and power at hip and knee
3
...
Reduced swing time and aerial time (key point)
5
...
Decreased average & peak vertical force compared against able-bodied athletes running at same speed
(Brüggeman et al
...
2009)
OP claimed Oliveira’s longer prostheses allowed greater stride length - OP strides were actually ~8% longer – it was a faster stride rate that gave Oliveira an
advantage
Pistorius’ competed in IPC and IAAF events - based on IPC regulations Pistorius allowed to compete at height of 1
...
84m
Oliveira only competed in IPC events
- Required to be less than 1
...
77m to 1
...
15m difference in height without prostheses
No single ratio or formula proclaiming correct leg length - clarification of rules needed
Small changes in mass, stiffness, thickness and curvature of blades affect different aspects of performance

Running Stride Rate and Length
Grabowski at al
...
, 2005) (IdC = Index of Coordination):
1
...
Opposition (one limb starts pull phase while other finishes push) (IdC = 0)
3
...
Exaggerated superposition (IdC > 10%)
Similar for Paralympic compared to able bodied but greater within group variation
Catch up - Linked to lower functional level, swimming speed and stroke length
- Differing ability to maintain stable streamlined position
Superposition - may improve performance by increasing stability in streamlined position but may reduce propulsive contribution of arms
Stroke Length, Rate and Kick Rate
Stroke length and stroke rate (Osborough et al
...
2009)
- Strong correlation between kick rate and swim time
- Increase in kick rate of 9
...
3% (~2
...
t) - depends on hand rim diameter and force-velocity characteristic
- High levels of strength and rate of force development needed

Trunk position and strength (Moss et al
...
, 2009)
- At low speeds, medium diameter (0
...
34 m) produced lowest physiological responses – hand rim moving at slower velocity so can move it at a higher
force
- Minor adjustments can make considerable changes
Contrast the design of wheelchairs used for team sports compared to racing
...

Implications on conditioning and tactics
Not all wheelchair tennis players use self-propelled wheelchairs
Cycling
More rigid prosthetic limbs than for running
Cycling vs running for amputees = energy storage in prosthetic limb:
- Lack of dorsiflexion torque requires hip and knee flexors to increase work in recovery phase
- Lack of plantar flexor torque requires hip and knee flexors to increase work in push phase
Asymmetry:
- Athletes with unilateral amputation
- Amputees produce lower torques, more pedal work & force asymmetry compared to able bodied (Childers et al
...
, 2008):
- Crank length influences efficiency with greater efficiency using shorter crank (180 mm v 220 mm)
- General trend that higher cadence more efficient
- More pronated handgrip angle (+30°) produces greater power output than those commonly used (+10o and -15o) (Krammer et al
...
g
...

- Flight height (H2) – determined by take-off velocity, COG velocity, vertical impulse
- Clearance height (H3) – determined by position of body in relation to COG
Take off velocity determined by force and time (net impulse) at take-off phase

Height Contribution(Genadi Avdeyenko: 1988 Olympics)
Distance (m)
Percentage (%)
Take-off height
1
...
07
45
Clearance height
-0
...
38
100
Conrad & Ritzdorf (1990)

Biomechanical Principles of High Jump
COG – location will change as body parts move, using arms more, full extension at take-off, also taller people have a higher COG (stature)
Impulse-momentum relationship:
- Impulse = force x time
Force = mass x acceleration
Acceleration = velocity / time
- Momentum = mass x change in velocity
- High jumper generates max vertical forces at take-off – approximately 3x bw for a world class athlete (Watkins, 1999)
- Fast approach run helps exert a greater vertical GRF (Dapena & Chung, 1988)
Projectile motion - Factors influencing jump height
- Positive relationship between horizontal run-up velocity and vertical take-off velocity (Dapena et al
...
Deterministic Model
Fig 2
...
g
...
2) Wind-up
...
4) Follow through
In high jump example preparation could be defined as the last stride before they
take-off
Physical Requirements
Approach - build up speed (and control the speed, not too fast)
Preparation - Leg position = proprioception
- Force acceptance =isometric/eccentric strength
Take-off - Stretch-shorten cycle =plyometric strength
- Force generation = concentric strength, power
Flight - Body position = proprioception and core stability
Tells you the things to train and how to improve a particular phase of the jump – performance enhancement
Injury Risks
High loading forces at touch down – necessary to gain vertical impulse
Factors effecting loading – approach speed, knee flexion at touch down, leg stiffness
Training Exercises
What exercises to use? – based on physical requirements
Movement specificity:
- Joints: initial, final and ROM
- Muscles: stretch-shorten cycle
- Loading: type, magnitude and rate
- Speed of movement
- Symmetry: are both legs doing the same thing?
- Sequence of movement
- Balance

Event

High Jump

Phases

Defining
Moments

Description

Purpose/
outcome

Movement
principles
(mechanical
terminology)

Acceleration
...

Generate large yet controlled
velocity
...

Extended leg at touch
down

Compression
...

Knee flexion ROM
...

Bar clearance
...


Ensure appropriate bar
clearance
...

Whole body speed
...

Lower limb kinematics
...

Maximise vertical impulse and
COM height
...

Kinetic chain
...

COM and body position
...

Control of body rotation
...


Variable

Definition

Equations
Units

Name

Symbol

Linear displacement

s

Linear displacement (arc)

d

Angular displacement

θ

Symbol
Straight line in specific direction from start position to end position

Name

-

Radians (rad)
Difference between the initial and final positions

Metres (m)

d = r
...
s )

Angular velocity

ω

Rate of angular motion in a specific direction

Degrees/radians per second ( s / rad
...
s )

a = Δv/t

Change in velocity/time

Angular acceleration

ά

Rate of change of angular velocity

Degrees/radians per second squared ( os-2 / rad
...
a

Moment of force/Torque

τ

A force that causes rotation

Newton metres (N
...
d

Moment of inertia

I

Angular equivalent of mass and distribution of mass
...
m )

I = m
...
m
...
v

Mass x linear velocity

Angular momentum

L

Reluctance of a body to alter angular speed and direction

Kilogram metres squared per second (kg
...
s-1)

L = I
...
s)

I = F
...
m
...
t

Torque x time

Mechanical advantage

MA

-

MA = Rf/Ef

Load force/effort force

Work

W

Product of chemical energy used

Joules (J)

W = F
...
81))
Force x perpendicular distance from axis to line of force
application

Force x displacement
Angular equivalent = torque x angle
Work/time
Force x velocity

Estimating Joint Torque:
τknee = W
...
dGRF + m
...
da + I
...
of segment) + (moment of inertia x angular acceleration
...
ACL injury – Griffin et al, 2000 – 70% of ACL injuries occur during non-contact situations
– Hughes, 2014 – gender differences of biomechanical risk factors of ACL injury
2
...
, 2000 – marker systems and attachment methods
3
...
, 2005 – gender differences in frontal and sagittal plane biomechanics during drop landings
– Alexander & Vernon, 1975 – some discrepancy between quasi-static and inverse dynamic models in drop landings (120N
...
m)
4
...
, 2012 – strength training, recreational soccer and running on SSC muscle performance during countermovement jumping (JJJ)
5
...
, 1994 – coordination definition: relative timing of motion between body segments, degree of coupling (JC – badminton)
– Hughes & Watson, 2008 – DRP angles between left and right leg joints (rather than adjacent joints) during landings
– Anderson and Sidaway, 1994 – Angle-angle diagrams
...
Trained participants displaced lower CRP variability in knee:ankle and hip:knee couplings than untrained
...
, 2005 – joint coupling patterns and variability of rearfoot and tibia during running with 2 types of orthotic devices
...
Used vector coding
6
...
, 2012 – review of models of vertical, leg and knee stiffness for running, jumping or hopping tasks and leg stiffness definition
– Watkins, 1999 – kinetic chain definition – transmission of forces between body segments during posture or movement
– Hobara et al
...
general population
– Hobara et al, 2008 – greater leg stiffness in power athletes than endurance athletes
– McMahon & Cheng, 1990 and Cavagna, 1975 – two methods for calculating COM displacement for vertical stiffness
– Faley & Morgenroth, 1999 – leg stiffness and joint stiffness calculations
– Butler et al
...
Barefoot running – Lieberman et al
...
Nature journal
– Leiberman, 2012 – evolutionary perspective of barefoot running



---