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The Lower Limb as a System of Levers
Andy HorwoodIndependent Researcher & Lecturer.
Product Research & Design HealthyStep LtdVisiting Lecturer & Fellow Staffordshire University
● Why do levers matter?● What is stress?● What is strain?● What is angular moment?● What are the classes of levers?● Where are these lever classes in the lower limb?
What influence does this piffle have on pathology?
What Is This Lecture All About?
ENERGETICS (the study of energy in systems)
Efficient Energetic = Efficient Biomechanics = Survival = Evolution = Efficient Energetics
Why Do Levers Matter?
Levers affect mechanical efficiency = Effect our energetics.Efficient Biomechanics + Healthy MSK Tissues = Efficient Energetics
Levers are ONE of the methods used to achieve mechanical efficiency
Force applied a structure
● Connective Tissue Tethering● Muscle Contraction● Extrinsic Factors● GRF
● Newton’s 1st ○ Law Of Inertia/Momentum
● Newton’s 2nd ○ Law (F =M X A)
● Newton’s 3rd Law○ (Every Action Has Equal & Opposite Reaction)
What is stress?
GRF over time
● Connective Tissue Tethering● Muscle Contraction● Extrinsic Factors● GRF
● Newton’s 1st ○ Law Of Inertia/Momentum
● Newton’s 2nd ○ Law (F =M X A)
● Newton’s 3rd Law○ (Every Action Has Equal & Opposite Reaction)
What is stress?
Force Applied A Structure
Large Movements of CoMPotential Energy
CoM athighest point
Kinetic Energy
Kinetic Energy
HS MS TS
Ankle Plantarflexion
Foot Flat
Strain = Deformity = Work Done
WORK CAN BE POSITIVE OR NEGATIVE
MOMENTUM ROTATING AROUND AN AXIS(remember joint axes are instantaneous)
•Moment of Inertia x Angular Velocity I x ω = L
•What is moment of inertia? •Like mass but considers where the mass is distributed to the axis of rotation. •I = Σ (mn . r 2/n).
WHAT IS ANGULAR MOMENTUM?
Angular velocity number of degrees (or rotations) per second
● If forces either side of an axis = rotation A● If forces are over axis = no rotation B
Angular momentum
A B
If forces equal on same side forces furthest away from axis create the direction of rotation. AIf unequal forces are equal distance from axis the larger force creates the direction of rotation. B
A B
Simple Foot-ankle Model
LATERALMEDIAL
Why Shoes & Leg Shape Matter
CoM & Gravity = CoG
BWV BWV
GRF GRF
Right
The nearer the forces to the axis the easier for muscles to control rotations. Shoes matter!
With The Right Shoe
Linear Momentum
FLEXION / EXTENSION (sagittal plane)
Joint motion is ANGULAR MOMENTUM, created by GRF and CoM interaction or
muscle contraction
Most muscle resists angular moment in closed chain.(eccentric contraction)
Heel Contact
CoM
CoG
Early Loading Response
plantarflexion moment
flexion
End Loading Response
Foot flat● CoM lowest● Kinetic energy used up
Early Midstance
True Midstance
● CoM at maximum height● High Potential energy
Late Mid-Stance
● Potential turns to kinetic energy
Terminal Stance
E
Pre-Swing
Classes of Levers
FR or E
E or R
F
ER
ER F
● 1st CLASS LEVER○ Effort on opposite sides of
fulcrum ■ (inefficient or efficient)
● 2nd CLASS LEVER○ Effort furthest away from
fulcrum ■ (efficient)
● 3rd CLASS LEVER○ Resistance furthest away
from fulcrum ■ (inefficient)
Classes of Levers
● 1st CLASS LEVER○ Effort on opposite sides of
fulcrum ■ (inefficient or efficient)
● 2nd CLASS LEVER○ Effort furthest away from
fulcrum ■ (efficient)
● 3rd CLASS LEVER○ Resistance furthest away
from fulcrum ■ (inefficient)
ER F
E/RE/R
F
R
F
E
Hip Abductors in Single limb support
Lower Limb Example - 1st Class
RE E F
RF
E RER
XX
Swing limb
Swing limb
● Achilles at heel lift● MTP joints are the
fulcrum(s)
E
R
F
CoM
E R
Lower Limb Example - 2nd Class
R
F
E
Lower Limb Example - 3rd Class Lever
FE
R
F
E
R
FE
R
Mechanical efficient or physiologically efficient/speed
Why Choose Inefficient 3rd Class?
E
E
R
R
Muscle Contraction - Levers Principles
ER
F
R
R
R
effort is > than resistance
effort is = to the resistance
effort is < than resistance
Hip Abductor Dysfunction
Class 1 Lever Pathomechanics
ISOMETRIC ECCENTRIC
F F
E ERR
E
R
Isometric Eccentric
Class 2 Lever Pathomechanics.
F F F
E
R
E
R R
E
Wheelbarrow Foot
E
RR
F
●○ Loading rate○ Stride length
Class 3 lever dysfunction
R
BWV
GRF
● Tibialis Anterior Tendinopathy● Anterior shin splint
E R
● Tibial anterior stresses acceptable ● Angular momentum controlled ● Loading rate acceptable
● Tibial anterior stresses to high● Angular momentum uncontrolled● Loading rate too high
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