Evaluation of Cushioning Properties of Running Footwear

Evaluation of Cushioning Properties of Running Footwear

D. Gordon E. Robertson, Ph.D.*

Joe Hamill, Ph.D.**

David A. Winter, Ph.D.#

* School of Human Kinetics,

University of Ottawa, Ottawa, CANADA

** Dept. of Exercise Science,

University of Massachusetts, Amherst, USA

# Kinesiology Dept., University of Waterloo,

Waterloo, CANADA

Introduction

• most mechanical analyses assume rigid body mechanics

• during initial contact and toe-off the foot may not act as a rigid body especially if footwear is worn

• modeled as a deformable body, cushioning properties of foot/shoe can be evaluated under ecologically valid conditions

Purpose

• measure the deformation power of foot during running to determine whether the cushioning properties of footwear can be distinguished

Methods

• nine runners (seven male, two female) having men’s size 8 shoe size

• video taped at 200 fields/second

• five trials of stance phase of running

• speed: 16 km/h (4.4 m/s, 6 minute/mile)

• ground reaction forces sampled at 1000 Hz

• two conditions:

– soft midsole (40-43 Shore A durometer)

– hard midsole (70-73 Shore A durometer)

Methods

• foot’s mechanical energy and rate of change of energy computed (E/t)

• inverse dynamics to calculate ankle force (F) and moment of force (M)

• ankle force power:Pf = F . v

• ankle moment power: Pm = M

Methods

power deformation computed as:

Pdef = E/t - (Pf + Pm)

• assuming no power loss/gain to/from ground

• assuming non-rigid (deformable) foot

Foot powers

0.00 0.05 0.10 0.15 0.20

Time (seconds)

-2000.

-1500.

-1000.

-500.

0.

500.

1000.

1500.

2000.

Pow

er (

wat

ts)

Trial: F1C1T4Force powerMoment powerTotal powerEnergy rateDeformation power

Deformation powers

0.00 0.05 0.10 0.15 0.20

Time (seconds)

-2000.

-1500.

-1000.

500.

0.

500.

1000.

Pow

er (

wat

ts)

Trial: F1C1 soft solesTrial 1Trial 2Trial 3Trial 4Trial 5

Mean deformation powers(subj. J1)

Percentage of stance

Pow

er (

wat

ts)

0 10 20 30 40 50 60 70 80 90 100

Hard sole

0 10 20 30 40 50 60 70 80 90 100-2500

-2000

-1500

-1000

-500

0

500

1000

Soft sole

Mean deformation powers(subj. F1)

0 10 20 30 40 50 60 70 80 90 100Percentage of stance

Pow

er (

wat

ts)

Hard sole

0 10 20 30 40 50 60 70 80 90 100-2500

-2000

-1500

-1000

-500

0

500

1000Soft sole

Mean deformation powers(subj. L3)

Percentage of stance

Pow

er (

wat

ts)

-2500

-2000

-1500

-1000

-500

0

500

1000

0 10 20 30 40 50 60 70 80 90 100

Hard sole

0 10 20 30 40 50 60 70 80 90 100

Soft sole

Mean deformation powers(subj. L4)

Percentage of stance

Pow

er (

wat

ts)

-2500

-2000

-1500

-1000

-500

0

500

1000

0 10 20 30 40 50 60 70 80 90 100

Hard sole

1000 10 20 30 40 50 60 70 80 90

Soft sole

Mean deformation powers(subj. L5)

Percentage of stance

Pow

er (

wat

ts)

-2500

-2000

-1500

-1000

-500

0

500

1000

0 10 20 30 40 50 60 70 80 90 100

Hard sole

0 10 20 30 40 50 60 70 80 90 100

Soft sole

Mean deformation powers(subj. L6)

Percentage of stance

Pow

er (

wat

ts)

-2500

-2000

-1500

-1000

-500

0

500

1000

0 10 20 30 40 50 60 70 80 90 100

Hard sole

0 10 20 30 40 50 60 70 80 90 100

Soft sole

Mean deformation powers(subj. L9)

Percentage of stance

Pow

er (

wat

ts)

-2500

-2000

-1500

-1000

-500

0

500

1000

0 10 20 30 40 50 60 70 80 90 100

Hard sole

0 10 20 30 40 50 60 70 80 90 100

Soft sole

Mean deformation powers(subj. L10)

Percentage of stance

Pow

er (

wat

ts)

-2500

-2000

-1500

-1000

-500

0

500

1000

0 10 20 30 40 50 60 70 80 90 100

Hard sole

0 10 20 30 40 50 60 70 80 90 100

Soft sole

Mean deformation powers(subj. L11)

Percentage of stance

Pow

er (

wat

ts)

-2500

-2000

-1500

-1000

-500

0

500

1000

0 10 20 30 40 50 60 70 80 90 100

Hard sole

0 10 20 30 40 50 60 70 80 90 100

Soft sole

Results

• in all nine subjects there was an initial period of negative work

• in six subjects a brief period of positive work followed

• in seven subjects a period of negative work occurred in midstance

• in eight subjects there was a period of positive work immediately before toe-off

Discussion

• the initial negative work was assumed to be due to energy absorption by the materials in the heel of the shoe and/or the tissues in the heel

• the subsequent positive work was likely due to energy return from, most likely, the shoe

• negative work during midstance may be due to midsole deformation or work by moment at metatarsal-phalangeal joint

• the final burst of power was assumed to be due to work done by the muscle moment of force across the metatarsal-phalangeal joint

Conclusions

• there was no significant difference between the impact characteristics of the two types of shoe durometer

• assumption of rigidity of foot-shoe is not appropriate

• power deformation patterns were consistent within subjects but varied considerably across subjects

• subjects probably adapted to the shoe impact characteristics to mask the differences in the shoe’s durometer

Hypotheses

• subjects probably adapted to the shoe impact characteristics to mask the differences in the shoe’s durometer

• need to test methodology on a mechanical analogue that can consistently deliver a footfall to a force platform