Running Shoes

Question 1

What are Running Shoes Purposes? 5

Answer 1

• Protection
• Injury prevention
  – Motion control
  – Attenuation of impact forces
• Provide traction
• Comfort
• Performance

Question 2

Lower Limb Anatomy - How many bones

Answer 2

26 bones

Question 3

What is the Running Shoe Anatomy? 4 things

Answer 3

Question 4

Footwear features in performance? 4

Answer 4

• Shoe mass
• Longitudinal bending stiffness (LBS)
• Midsole material
• Heel Thickness

Question 5

The change in running performance with shoe mass

Answer 5

• 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

Question 6

What does Shoe Mass do to the Biomechanics?

Answer 6

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

Question 7

Longitudinal Bending Stiffness (LBS)

Answer 7

Resistance against bending with external load applied perpendicularly to longitudinal axis (x-axis)

Question 8

LBS Technology and advantages of them and what else is available

Answer 8

• 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

Question 9

Mechanical Testing of LBS?

Answer 9

• 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

Question 10

Longitudinal Bending Stiffness Equation

Answer 10

Question 11

Running Economy & LBS

Answer 11

• Stiff ~1% RE improvement
• U-Shaped
• Optimal longitudinal stiffness
• ↑ body mass greater ↓ oxygen consumption
• Finite stiffness in a given range of mass

Question 12

Why is the Nike Vapor 4% called 4%?

Answer 12

Vapor Fly ↓ cost of running 4.0% is lower compared to othermarathon racing shoes

Question 13

How to Minimise MTP (Joint) Energy Lost

Answer 13

With a stiffer LBS it decreases negative energy at MTP and increase positive energy at MTP.

Question 14

2 strategies for joint/angle moment

Answer 14

• Increase in joint moments increase push-off time
• Decrease in ankle moment increase push-off time

Question 15

MTP Critical Stiffness Equation?

Answer 15

Question 16

Running Economy & LBS

Answer 16

Local minimum metabolic cost near critical stiffness

Question 17

What happens to the MTP angle as LBS bending stiffness increases?

Answer 17

Increased bending stiffness descreases maximum flexion of MTP
* Restriction of natural motion determinants of the local minimum of running energetics

Question 18

What is the Teeter-Totter Effect?

Answer 18

• 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)

Question 19

Study: Longitudinal Bending Stiffness does not effect the running economy of the Nike Vapour fly Shows, Outcomes, limitations

Answer 19

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

Question 20

The point of the Midsole Material?

Answer 20

Protective medium that provides interface between the ground and musculoskeletal system. Intended for the redistribution of force or shock attenuation, or both

Question 21

Examples of Midsole material

Answer 21

• 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

Question 22

Midsole Mechanical Testing

Answer 22

• 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

Question 23

Critical requirements for the midsole in Energy Storage & Return Theory? 5

Answer 23

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

Question 24

What does a change in the midsole do to the Running Economy?

Answer 24

• Statistically significant improvement in RE
• Different shoe stiffness & hysteresis
• Difficult to know attribute of cushioning which caused improvement

Question 25

New EVA vs. New PEBA midsole material test

Answer 25

Running economy decreases by 1.8% in PEBA

Question 26

Muscle Tuning Paradigm 4 steps

Answer 26

1. Impact forces are input signals ( Heel strike 5 – 20Hz)
2. Sensed by central nervous system (CNS)
3. Muscle tuning (EMG activity) to minimise soft tissue
   vibration (avoid resonance)
4. Effects of muscle tuning seen in performance & comfort

Question 27

Muscle Activity Purpose? 6

Answer 27

• Leg geometry
• Joint stiffness
• Vibrations of soft-tissue
• Joint loading
• Stability during ground contact
• Propulsion

Question 28

What are the Footwear Engineering Considerations?

Answer 28

• 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