Transcript Power production during swim starting

Two-segment Model of the Foot
for 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-toend
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 selfselected 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 of
two-segment foot
Methods
• mechanical energy and rate of change of
energy computed (DE/Dt)
• inverse dynamics to calculate net forces (F)
and moments of force (M)
• force powers:
Pf = F . v
• moment powers:
Pm = M w
• total power:
Pt = S Pf + S Pm
• power imbalance:
Pi = DE/Dt - Pt
Results (subject 1)
• pause to show
animation
Ang. velocity, moment and
power of the ankle joint
(WN01GR)
10.
Dorsiflexing
0.
-10.
100.
Trial: WN01GR
Ang. vel.
Net moment
Power
Plantar flexing
Dorsiflexor
0.
-100.
250.
Plantar flexor
Concentric
0.
-250.
-500.
Eccentric
IFS
0.0
0.1
0.2
0.3
Time (s)
0.4
IHO
0.5
ITO
0.6
0.7
0.8
Ang. velocity, moment and
power of the ankle joint
(WN01GR2)
10.
Dorsiflexing
0.
-10.
100.
Trial: WN01GR2
Ang. vel.
Net moment
Power
Plantar flexing
Dorsiflexor
0.
-100.
250.
Plantar flexor
Concentric
0.
-250.
-500.
Eccentric
IFS
0.0
0.1
0.2
0.3
Time (s)
0.4
IHO
0.5
ITO
0.6
0.7
0.8
Ang. velocity, moment and
power of the MP joint
(WN01GR2)
10.
Dorsiflexing
0.
-10.
100.
Trial: WN01GR2
Ang. vel.
Net moment
Power
Plantar flexing
Dorsiflexor
0.
-100.
250.
Plantar flexor
Concentric
0.
-250.
-500.
Eccentric
IFS
0.0
0.1
0.2
0.3
Time (s)
0.4
IHO
0.5
ITO
0.6
0.7
0.8
Foot powers
(WN01GR)
2000.
Trial: WN01GR
Floor power
Force power
Moment power
Total power
Energy rate
Power imbalance
1500.
1000.
500.
0.
-500.
-1000.
-1500.
IFS
-2000.
0.00
0.10
0.20
0.30
0.40
Time (seconds)
IHO
0.50
ITO
0.60
0.70
Forefoot powers
(WN01GR2)
2000.
Trial: WN01GR2
Floor power
MP force power
MP moment power
Ff total power
Ff energy rate
Ff power imbalance
1500.
1000.
500.
0.
-500.
-1000.
-1500.
IFS
-2000.
0.00
0.10
0.20
0.30
0.40
Time (seconds)
IHO
0.50
ITO
0.60
0.70
Rearfoot powers
(WN01GR2)
2000.
Trial: WN01GR2
MP force power
MP moment power
Ankle force power
Ankle moment power
Rf total power
Rf energy rate
Rf power imbalance
1500.
1000.
500.
0.
-500.
-1000.
-1500.
-2000.
0.00
IFS
0.10
0.20
0.30
0.40
Time (seconds)
IHO
0.50
ITO
0.60
0.70
Results (subject 2)
• pause to show
animation
Ang. velocity, moment and
power of the ankle joint
(WN01JS)
10.
Dorsiflexing
0.
-10.
100.
Trial: WN01JS
Ang. vel.
Net moment
Power
Plantar flexing
Dorsiflexor
0.
-100.
250.
Plantar flexor
Concentric
0.
-250.
-500.
Eccentric
IFS
0.0
0.1
0.2
0.3
0.4
Time (s)
0.5
IHO
0.6
0.7
ITO
0.8
0.9
1.0
Ang. velocity, moment and
power of the MP joint
(WN01JS2)
10.
Dorsiflexing
0.
-10.
100.
Trial: WN01JS2
Ang. vel.
Net moment
Power
Plantar flexing
Dorsiflexor
0.
-100.
250.
Plantar flexor
Concentric
0.
-250.
-500.
Eccentric
IFS
0.0
0.1
0.2
0.3
0.4
Time (s)
0.5
IHO
0.6
0.7
ITO
0.8
0.9
1.0
Ang. velocity, moment and
power of the ankle joint
(WN01JS2)
10.
Dorsiflexing
0.
-10.
100.
Trial: WN01JS2
Ang. vel.
Net moment
Power
Plantar flexing
Dorsiflexor
0.
-100.
250.
Plantar flexor
Concentric
0.
-250.
-500.
Eccentric
IFS
0.0
0.1
0.2
0.3
0.4
Time (s)
0.5
IHO
0.6
0.7
ITO
0.8
0.9
1.0
Foot powers
(WN01JS)
2000.
1500.
1000.
Trial: WN01JS
Floor power
Force power
Moment power
Total power
Energy rate
Power imbalance
500.
0.
-500.
-1000.
-1500.
-2000.
IFS
0.00
0.10
0.20
IHO
0.30
0.40
0.50
0.60
Time (seconds)
0.70
ITO
0.80
0.90
Forefoot powers
(WN01JS2)
2000.
Trial: WN01JS2
Floor power
MP force power
MP moment power
Ff total power
Ff energy rate
Ff power imbalance
1500.
1000.
500.
0.
-500.
-1000.
-1500.
-2000.
IFS
0.00
0.10
0.20
IHO
0.30 0.40 0.50 0.60
Time (seconds)
0.70
ITO
0.80
0.90
Rearfoot powers
(WN01JS2)
2000.
1500.
1000.
Trial: WN01JS2
MP force power
MP moment power
Ankle force power
Ankle moment power
Rf total power
Rf energy rate
Rf power imbalance
500.
0.
-500.
-1000.
-1500.
-2000.
IFS
0.00
0.10
0.20
IHO
0.30
0.40
0.50
0.60
Time (seconds)
0.70
ITO
0.80
0.90
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