First published online December 15, 2004
Journal of Experimental Biology 208, 41-53 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01305
Joint work and power associated with acceleration and deceleration in tammar wallabies (Macropus eugenii)
C. P. McGowan1,*,
R. V. Baudinette2 and
A. A. Biewener1
1 Concord Field Station, Department of Organismic and Evolutionary Biology,
Harvard University, Cambridge, MA 02138, USA
2 Department of Environmental Biology, University of Adelaide, Adelaide, SA
5003, Australia
View larger version (17K):
[in a new window]
|
Fig. 1. A schematic diagram of the linked segment model used to calculate joint
moments, power and work. (A) The internal angles that were measured. Angles
( ) were measured at hip (h), knee (k), ankle (a) and metatarsophalageal
joint (MP). (B) Elements of the linked segment model used in the inverse
dynamics calculations, where m is the mass of each segment,
I is the mass moment of inertia of each segment and
Fx and Fy are the horizontal and
vertical ground reaction forces (GRF), respectively. The center of pressure of
the GRF on the foot was determined by the force plate.
|
|
View larger version (16K):
[in a new window]
|
Fig. 2. Representative GRF recordings from (A) a large acceleration trial, (B) a
steady speed trial and (C) a large deceleration trial, normalized to
percentage of stance time. The insets show the average limb position at the
time of first contact, midstance and last contact relative to the orientation
of the GRF vector (red broken line). Note the broken red line does not
represent the magnitude of the GRF.
|
|
View larger version (13K):
[in a new window]
|
Fig. 3. The mean vertical (VGRF, squares), propulsive
(+HGRF, triangles) and breaking
(-HGRF, circles) forces in xBW
versus acceleration. During accelerations, both
VGRF and +HGRF increased with
acceleration; however, the trend for VGRF was not
significant (r2=0.93, P<0.0001;
r2=0.23, P=0.072, respectively). During
decelerations, only -HGRF was significantly correlated
with acceleration (r2=0.89, P<0.0001).
|
|
View larger version (12K):
[in a new window]
|
Fig. 4. Graphs of (A) limb protraction angle, (B) limb retraction angle and (C)
limb excursion angle versus acceleration. During acceleration trials
(triangles), limb protraction angle did not change significantly with
acceleration, while retraction angle increased with increasing accelerations.
In deceleration trails (squares), both limb protraction and retraction angles
increased with increasing deceleration magnitude. Limb excursion angle
increased linearly with both acceleration and deceleration magnitude. See text
for further details.
|
|
View larger version (15K):
[in a new window]
|
Fig. 5. Graphs of the average change in joint angle during stance for the hip,
knee, ankle and metatarsophalageal joint (MP) during accelerations (green),
steady speed (black) and decelerations (red). Solid lines are the average of
four trials for each condition. The mean accelerations of these groups were:
5.88±0.80 m s-2, -0.07±0.45 m s-2 and
-5.27±0.86 m s-2 for accelerations, steady speed and
decelerations, respectively. Standard errors for each joint angle curve have
been omitted for the sake of clarity.
|
|
View larger version (15K):
[in a new window]
|
Fig. 6. A graph showing the net angle change during stance at each joint as a
function of acceleration. Positive values represent net joint extension while
negative values represent net joint flexion. The results of linear regressions
showed significant correlations at all joints (hip:
r2=0.50, P<0.0001; knee:
r2=0.47, P<0.0001; ankle:
r2=0.51, P<0.0001; MP:
r2=0.19, P=0.017).
|
|
View larger version (17K):
[in a new window]
|
Fig. 7. Graphs of total joint moments (tot), including inertial and gravitational
components (solid lines) and external joint moments (ext, dotted lines) from a
representative trial for each condition: (A) acceleration, 5.97 m
s-2, (B) steady speed, -0.41 m s-2 and (C) deceleration,
-5.99 m s-2. During accelerations, moments reach a peak later in
stance and are maintained for a longer duration of the stance period, as
compared to steady speed trials. Conversely, during decelerations the moments
reach a peak early in stance and fall to near zero for the later part of
stance. Peak moments for all joints remains relatively constant across trails.
Note that the difference between total joint moments and external joint
moments is small and can only be seen at the hip.
|
|
View larger version (17K):
[in a new window]
|
Fig. 8. Total joint power (tot, solid colored lines), external joint power (ext,
dotted colored lines) and summed limb power (broken black lines) for the
representative trials shown in Fig.
6. The majority of the power for changing speed is produced at the
hip (red) and ankle (blue). Peak powers at the knee (green) increase during
accelerations and decelerations, but the net work remains relatively constant.
The MP (black) produces more negative power with increased accelerations.
|
|
View larger version (12K):
[in a new window]
|
Fig. 9. Net work produced at each joint per kg body mass versus
acceleration. The slope of regression lines was steepest at the ankle,
indicating that the modulation of limb work during accelerations and
decelerations occurred primarily at this joint. Work at the hip and MP also
had a significant relationships with acceleration but with shallower slopes
than at the ankle. The amount of work done at the knee was low and independent
of acceleration. Linear regressions are: hip,
y=0.095x+0.954, r2=0.035,
P<0.001; knee, y=0.021x+0.347,
r2=0.05, P=0.256; ankle,
y=0.302x+0.024, r2=0.83,
P<0.0001; MP, y=-0.08x-0.997,
r2=0.39, P<0.001.
|
|
View larger version (17K):
[in a new window]
|
Fig. 10. Center of mass (CoM) work (filled triangles) and summed limb work (open
squares) plotted against acceleration. The slope of the regression line for
the summed limb work (broken line) was significantly lower then that for the
center of mass work (solid line). Thus, at the maximum accelerations and
decelerations, the work done by the limbs did not account for all of the work
done on the center of mass. This suggests that the trunk and tail may also be
recruited to power changes in speed (see Discussion). Linear regressions are:
CoM work, y=0.530x+0.022, r2=0.97,
P<0.0001; limb work, y=0.338x+0.328,
r2=0.87, P<0.0001.
|
|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati 
Twitter What's this?
© The Company of Biologists Ltd 2005
