Running Shoes Flashcards
What are Running Shoes Purposes? 5
- Protection
- Injury prevention
– Motion control
– Attenuation of impact forces - Provide traction
- Comfort
- Performance
Lower Limb Anatomy - How many bones
26 bones
What is the Running Shoe Anatomy? 4 things
Footwear features in performance? 4
- Shoe mass
- Longitudinal bending stiffness (LBS)
- Midsole material
- Heel Thickness
The change in running performance with shoe mass
- Shoe mass degrades RE
- Slows 3 km time-trial
- Reduction shoe mass by 100 g per shoe reduce marathon record by ~ 0.78% or 57.5 seconds
- Unmodified temporal and kinematic variables
- Increase in mechanical work
What does Shoe Mass do to the Biomechanics?
Temporal and kinematic variables unmodified by load
Increase mechanical work
– Inertial changes
– Rather than large kinematic change
– Increase in work performance by muscles
– 13% increase MOI
Longitudinal Bending Stiffness (LBS)
Resistance against bending with external load applied perpendicularly to longitudinal axis (x-axis)
LBS Technology and advantages of them and what else is available
- Carbon fibre plates
- Advantages: high stiffness, high tensile strength, low weight
- adidas adios pro and Takumi sen 8 have Curved carbon infused rods
- Laser sintering Nylon
Mechanical Testing of LBS?
- 3-point bend test
- Displacement driven
- Measure force required for defined displacement
- Impactor/loading pin perpendicular to longitudinal axis
- Stiffness
– Slope of force displacement curve
Longitudinal Bending Stiffness Equation
Running Economy & LBS
- Stiff ~1% RE improvement
- U-Shaped
- Optimal longitudinal stiffness
- ↑ body mass greater ↓ oxygen consumption
- Finite stiffness in a given range of mass
Why is the Nike Vapor 4% called 4%?
Vapor Fly ↓ cost of running 4.0% is lower compared to othermarathon racing shoes
How to Minimise MTP (Joint) Energy Lost
With a stiffer LBS it decreases negative energy at MTP and increase positive energy at MTP.
2 strategies for joint/angle moment
- Increase in joint moments increase push-off time
- Decrease in ankle moment increase push-off time
MTP Critical Stiffness Equation?
Running Economy & LBS
Local minimum metabolic cost near critical stiffness
What happens to the MTP angle as LBS bending stiffness increases?
Increased bending stiffness descreases maximum flexion of MTP
* Restriction of natural motion determinants of the local minimum of running energetics
What is the Teeter-Totter Effect?
- Point of force application moves towards front of plate
- GRF produces upwards force at heel
- Force acts on heel at push-off (right location & time)
Study: Longitudinal Bending Stiffness does not effect the running economy of the Nike Vapour fly Shows, Outcomes, limitations
Limitations:
Forefoot bending measurements vary between studies
Technology in shoes varies & multiple components
Few studies capture performance & biomechanics
Definitions for modelling joints vary
More individualised analysis required
The point of the Midsole Material?
Protective medium that provides interface between the ground and musculoskeletal system. Intended for the redistribution of force or shock attenuation, or both
Examples of Midsole material
- Ethylene vinyl acetate (EVA) midsole
– Compression or injection moulding - Expanded thermoplastic polyurethane (TPU) pellets
- Pebax or PEBA (PolyEther-Block Amide) thermoplastic elastomers
- TPEE (Thermoplastic Polyester Elastomer)
- Alternative construction – Nylon blades
Midsole Mechanical Testing
- Compression Test
– Load & unload - Four key variables:
– Stiffness - Slope of loading curve
– Energy absorbed - Area under loading
– Energy returned - Area under unloading
– Hysteresis (energy lost) - Area between loading & unloading
Critical requirements for the midsole in Energy Storage & Return Theory? 5
Critical requirements:
* Energy returned must be substantial
* Energy returned at the right time
* Right frequency
* Energy at right location
* Compressed soft shoe return 1% of total energy required
What does a change in the midsole do to the Running Economy?
- Statistically significant improvement in RE
- Different shoe stiffness & hysteresis
- Difficult to know attribute of cushioning which caused improvement
New EVA vs. New PEBA midsole material test
Running economy decreases by 1.8% in PEBA
Muscle Tuning Paradigm 4 steps
- Impact forces are input signals ( Heel strike 5 – 20Hz)
- Sensed by central nervous system (CNS)
- Muscle tuning (EMG activity) to minimise soft tissue
vibration (avoid resonance) - Effects of muscle tuning seen in performance & comfort
Muscle Activity Purpose? 6
- Leg geometry
- Joint stiffness
- Vibrations of soft-tissue
- Joint loading
- Stability during ground contact
- Propulsion
What are the Footwear Engineering Considerations?
- For performance mass of shoe minimised
- Optimal midsole & longitudinal bending stiffness for a particular athlete
– Materials used
– Geometry of plate (LBS)
– Quantifying individual athlete biomechanics e.g. critical MTP stiffness - Bending stiffness may be specific to movement in question
- Standardised test for quantifying mechanical properties