Internal Work and Oxygen Consumption of Impaired and Normal Walking

1
Internal Work and Oxygen Consumption of Impaired
and Normal Walking

• Sylvain Grenier, M.A.
• D.G.E. Robertson, Ph.D.
• Biomechanics Laboratory
• School of Human Kinetics
• University of Ottawa

2
Purpose

• To compare the absolute work method with absolute
  power method in calculating work for impaired
  and normal gait, using physiological oxygen
  consumption measures as verification.

3
Methodology
Subject Trials

• subjects 4 male, 4 female
• Five normal gait trials per subject selected
• one trial each with splinted knee selected
• one trial each with splinted ankle selected
• the conditions were applied in random order

4
Methodology
Video

• three-dimensional video (30 Hz)
• markers both sides all joints
• Ariel digitization (60 Hz)
• Biomech Motion Analysis System

5
Methodology
Treadmill and Force

• VO2 standing baseline value (Pierrynowski,1980
  Stainsby,1980)
• 3 min walking VO2 steady state
• speed chosen, then metronome set
• force data collected for a full gait cycle
• 2 AMTI force platforms
• data from the first FS was carried over assuming
  symmetry (Cappozzo et al. 1976)

6
Work equations
work
Absolute
method



Absolute
power
method
External w
ork
N
J
N
'
W
E
W
M
t


(
)
D
D
w
å
å
å
ext
ext
i
i
S
j
j
i
i
j
i



1
1
1
Internal w
ork
N
J
N
é
ù
é
ù
'
W
E
W
W
M
t
W

-

ê
ú
-
'
D
D
w
å
å
å
ê
ú
int
T
ext
int
i
i
ext
i
j
j
ê
ú
i
j
i
ë
û



1
1
1
ë
û
7
Work equations

• Absolute Power (AP)
• integration of joint moment x angular velocity
  (power)
• assumes
• one muscle per joint
• no elastic storage
• pos. and neg. work equal mechanically

• Absolute Work (AW)
• change of instanteous energy
• location of summation limits energy exchanges
• I.e., if types of energy are separated then
  summed between and within exchanges are
  permitted, but between any two segments

8
Mechanical Efficiency
work
output
ME


x 100
x 100
work
input

ME
x 100
ME
x 100
Biomechanical cost internal work
mass velocity
9
Results Mechanical Efficiency
10
Mechanical Efficiency

• efficiency varies based on these assumptions
• baseline VO2
• value given to negative work
• if internal work is included
• calculation of antisymmetrical movements
• elastic energy storage
• assumption re biarticular muscles

11
Mechanical Efficiency

• calculated using AP method
• likely overestimates because
• includes elastic storage twice
• model assumes no intercompensation,
• biarticular muscles are not allowed
• negative power at one joint cannot be used to
  power the neighbouring joint
• Assume negative work positive work
• all increased Internal work/ O2 cost

12
Mechanical Efficiency

• calculated using AW method
• likely under estimates
• calculates net work vs. produced work
• assumptions of energy transfer limitations
  contradict Law of Conservation of energy
• I.e., potential to kinetic
• asymmetrical motion does not require energy
• all decreased internal work/ O2 cost

13
Differences between conditions
14
Differences between conditionswithin subjects
15
Direction of Difference
Wilcoxon signed ranks test

16
Normal Walking

• Normal walking data is similar to previous data
  from other published research

17
Mean of subjects Normal ankle
CFS
CTO
A2
A1

• A1 eccentric plantar flexor during early to
  midstance
• A2 concentric plantar flexor at push-off

18
Normal Knee
CFS
CTO
K1
K2
K4
K3

• K1 eccentric flexor moment absorbing impact
• K2 concentric extensor midstance to toe-off
• K3 eccentric flexor shortly before toe-off
  until max knee flexion
• K4 eccentric extensor late swing

19
Normal Hip
CTO
CFS
H3
H1
H1
H2

• H1 concentric extension moving CM forward
• H2 eccentric flexor lowering the CM
• H3 concentric flexor to swing the leg forward

20
Discussion

• Direction of difference
• perhaps humans are optimized for adaptability
  rather than efficiency
• LK trials tended to be lower
• induced changes in 3D or rotation not visible to
  planar analysis (Kerrigan, et al. (1997)
• values similar to other researchers
• Winter 1.09 J/kg.m (1979)
• our data
• AW 1.90 J/kg.m
• AP 3.05 J/kg.m

21
Discussion

• Efficiency
• obviously gt 100 not possible
• subtracting effect of elastic storage,
  biarticular muscles
• internal work increases, efficiency decreases to
  about 65-70
• compared to most efficient engines today about
  60

22
Conclusion

• AP IBC seems to indicate that locked knee
  internal work is less than in the normal case.
• Both AP AW seem to indicate that locked ankle
  gait is more efficient than normal
• Binomial test shows that AP method can
  distinguish between normal and impaired
  conditions.
• VO2 seems most consistent but not significant

23
Recommendations

• four or five cameras increase accuracy
• do a three dimensional analysis determine if
  energy lost is in the frontal plane
• use three force plates increase the accuracy
• have one extreme condition with both ankle and
  knee of one leg restricted

24
Acknowledgments

• Thanks to Heidi Sveistrup, Ph.D., for all her
  assistance and for the use of her lab.
• Thanks to Peter Stothart, Ph.D., for his guidance
  during my supervisors absence.