Two-segment Model of the Foot for Gait Analysis D. Gordon E. Robertson, Ph.D. Alison Cronin...

Two-segment Model of the Footfor Gait Analysis

D. Gordon E. Robertson, Ph.D.Alison Cronin

Biomechanics Laboratory,School of Human Kinetics,University of Ottawa, Ottawa, CANADA

Introduction

• Stephanyshn & Nigg (1997) showed negative work done by MP plantar flexors for running

• used EMED insole pressure system to partition floor reactions into two components

• pressure systems have no ability to distinguish components of a force only the magnitude of the resultant

• a single force platform cannot distinguish among several applied forces

• force plates computes a single resultant force--its components and centre of pressure

Solution

• use two force platforms• Gerber & Stuessi (1987)

developed equations to combine multiple force plates (available at www.health.uottawa.ca/

biomech/csb/archives/ kistler.pdf)

• arrange plates end-to-end

Solution

• subject lands foot across both plates

• in most cases little or no force occurs midstance

• can evaluate the subject using one or two ground reaction forces

Methods

• two male subjects• video taped at 60 fields/second• five trials of stance phase of walking at self-

selected speed• ground reaction forces sampled at 250 Hz

from two Kistler force plates• two conditions:

– one segment foot– two segment foot

Free-body diagram of one-segment foot

Free-body diagrams oftwo-segment foot

Methods

• mechanical energy and rate of change of energy computed (E/t)

• inverse dynamics to calculate net forces (F) and moments of force (M)

• force powers: Pf = F . v• moment powers: Pm = M • total power: Pt = Pf + Pm• power imbalance:Pi = E/t - Pt

Results (subject 1)

• pause to show animation

Ang. velocity, moment and power of the ankle joint

(WN01GR)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time (s)

-500.

-250.

0.

250.

-100.

0.

100.

-10.

0.

10.

Pow

er (W

)

M

omen

t (N

.m)

Ang

ular

vel

. (/s

)

Trial: WN01GRAng. vel.Net momentPower

IFS IHO ITO

Dorsiflexing

Plantar flexingDorsiflexor

Plantar flexorConcentric

Eccentric

Ang. velocity, moment and power of the ankle joint

(WN01GR2)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time (s)

-500.

-250.

0.

250.

-100.

0.

100.

-10.

0.

10.

Pow

er (W

)

M

omen

t (N

.m)

Ang

ular

vel

. (/s

)

Trial: WN01GR2Ang. vel.Net momentPower

IFS IHO ITO

Dorsiflexing

Plantar flexingDorsiflexor

Plantar flexorConcentric

Eccentric

Ang. velocity, moment and power of the MP joint

(WN01GR2)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Time (s)

-500.

-250.

0.

250.

-100.

0.

100.

-10.

0.

10.

Pow

er (W

)

M

omen

t (N

.m)

Ang

ular

vel

. (/s

)

Trial: WN01GR2Ang. vel.Net momentPower

IFS IHO ITO

Dorsiflexing

Plantar flexingDorsiflexor

Plantar flexorConcentric

Eccentric

Foot powers(WN01GR)

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70Time (seconds)

-2000.

-1500.

-1000.

-500.

0.

500.

1000.

1500.

2000.

Pow

er (W

)

Trial: WN01GRFloor powerForce powerMoment powerTotal powerEnergy ratePower imbalance

IFS IHO ITO

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70Time (seconds)

-2000.

-1500.

-1000.

-500.

0.

500.

1000.

1500.

2000.

Pow

er (W

)

Trial: WN01GR2Floor powerMP force powerMP moment powerFf total powerFf energy rateFf power imbalance

IFS IHO ITO

Forefoot powers(WN01GR2)

Rearfoot powers(WN01GR2)

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70Time (seconds)

-2000.

-1500.

-1000.

-500.

0.

500.

1000.

1500.

2000.

Pow

er (W

)

Trial: WN01GR2MP force powerMP moment powerAnkle force powerAnkle moment powerRf total powerRf energy rateRf power imbalance

IFS IHO ITO

Results (subject 2)

• pause to show animation

Ang. velocity, moment and power of the ankle joint

(WN01JS)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Time (s)

-500.

-250.

0.

250.

-100.

0.

100.

-10.

0.

10.

Pow

er (W

)

M

omen

t (N

.m)

Ang

ular

vel

. (/s

)

Trial: WN01JSAng. vel.Net momentPower

IFS IHO ITO

Dorsiflexing

Plantar flexingDorsiflexor

Plantar flexorConcentric

Eccentric

Ang. velocity, moment and power of the MP joint

(WN01JS2)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Time (s)

-500.

-250.

0.

250.

-100.

0.

100.

-10.

0.

10.

Pow

er (W

)

M

omen

t (N

.m)

Ang

ular

vel

. (/s

)

Trial: WN01JS2Ang. vel.Net momentPower

IFS IHO ITO

Dorsiflexing

Plantar flexingDorsiflexor

Plantar flexorConcentric

Eccentric

Ang. velocity, moment and power of the ankle joint

(WN01JS2)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Time (s)

-500.

-250.

0.

250.

-100.

0.

100.

-10.

0.

10.

Pow

er (W

)

M

omen

t (N

.m)

Ang

ular

vel

. (/s

)

Trial: WN01JS2Ang. vel.Net momentPower

IFS IHO ITO

Dorsiflexing

Plantar flexingDorsiflexor

Plantar flexorConcentric

Eccentric

Foot powers(WN01JS)

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90Time (seconds)

-2000.

-1500.

-1000.

-500.

0.

500.

1000.

1500.

2000.

Pow

er (W

)

Trial: WN01JSFloor powerForce powerMoment powerTotal powerEnergy ratePower imbalance

IFS IHO ITO

Forefoot powers(WN01JS2)

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90Time (seconds)

-2000.

-1500.

-1000.

-500.

0.

500.

1000.

1500.

2000.

Pow

er (

W)

Trial: WN01JS2Floor powerMP force powerMP moment powerFf total powerFf energy rateFf power imbalance

IFS IHO ITO

Rearfoot powers(WN01JS2)

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90Time (seconds)

-2000.

-1500.

-1000.

-500.

0.

500.

1000.

1500.

2000.

Pow

er (W

)

Trial: WN01JS2MP force powerMP moment powerAnkle force powerAnkle moment powerRf total powerRf energy rateRf power imbalance

IFS IHO ITO

Conclusions

• adding MP joint reduces error at foot-strike and toe-off

• plantar flexor moment at MP joint does both negative and positive work, but mainly negative

Questions?

Answers!

Where to go next?

Thank you