Biomedical Engineering Reference
In-Depth Information
Table 2.5 Energetic Figure of Merit,
σ
ω
, for the Average Walking Speed of 1.4 m/s
(3.1 mph) and for the Moderate Running Speed of 2.2 m/s (5 mph)
Body
Location
Walking
Running
Forward
Axis (m
2
/s
3
)
Vertical
Axis (m
2
/s
3
)
Lateral
Axis (m
2
/s
3
)
Forward
Axis (m
2
/s
3
)
Vertical
Axis (m
2
/s
3
)
Lateral
Axis (m
2
/s
3
)
Ankle
10
2.7
1.3
27
17
0.2
Knee
4
1.6
1.3
7
10
0.1
Hip
0.6
1.0
0.3
1.7
6
0.8
Chest
0.4
0.4
0.1
1
5
1
Wrist
0.15
0.23
0.07
6
3
0.8
Elbow
0.15
0.18
0.05
1.3
3
0.6
Shoulder
0.15
0.15
0.05
2
3
1.3
Side of the
head
0.1
0.28
0.05
0.5
2.5
0.3
Back of the
head
0.1
0.32
0.08
0.4
2.7
0.3
the ankle and from
2 to 3.5
G
for the knee and wrist. The other body
locations ranged from
B
0.7 to
B
1.5
G
along the forward axis, while
varying from
B
1.5 to
B
2.5
G
for the vertical axis. The higher accelera-
tions were found along the vertical axis rather than the forward axis,
except for the ankle. More detailed information can be found in
Romero (2010).
B
The energetic figure of merit for the different body locations is sum-
marized in
Table 2.5
. Available power can be estimated from
Eq. (2.7)
using the findings from the energetic figure of merit
σ
ω
. A first estima-
tion is made assuming a generator with a 1 g proof mass and a
Q
fac-
tor of 1, as shown in
Figure 2.6
. From the walking test, available
power levels below 0.5 mW are expected for most of the body loca-
tions, while the ankle and knee positions are able to provide higher
power levels. During the running test, the available power increases to
over 0.5 mW for most of the body locations along the vertical axis,
while the ankle and knee present significantly higher values.
A second estimation is based on the power density metrics of
Eq. (2.10)
assuming a proof mass density of 10 g/cm
3
and a
Q
factor
of 1.
Figure 2.7
shows the power densities for each body location at
different walking and running speeds. From these results, most of the
body locations provide less than 1 mW/cm
3
from walking, while
