Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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An insole with an opening.
The present invention relates to an article of
footwear and to a method of manufacturing the footwear.
During walking in footwear or bare feet ground
reaction forces (GRF's) act on the sole of the foot. After
the heel strikes the ground the GRF can rise to a maximum
of 100% to 140% of a person's body weight. As the force
increases to this maximum, usually, there is an oscillation
in the magnitude of impact force, known as the "heel strike
transient".
The impact force causes a mechanical shock wave
known as "impact shock" to propagate through the skeletal
system up to the skull. The energy of this shock wave is
dissipated as it propagates through bone, soft tissue and
muscle. The degree of dissipation can vary depending on
the motion and muscle action at the joints, particularly
the joints of the lower limbs, and any degenerative changes
that may have occurred at the joints.
The heel pad is a fatty fibrous structure that,
in a healthy state, is capable of absorbing up to 80% of
the heel strike peak acceleration propagated to the tibia.
The heel pad can have better shock absorbency than
Sorbothane (Trade Mark) or EVA foam which are commonly used
in good quality running shoes.
The effectiveness of the body's natural shock
absorbing mechanisms can be reduced in the case of
musculoskeletal disease, trauma or mechanical fatigue.
Lack of adequate shock absorption can cause larger
acceleration transients to propagate through the skeletal
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system. Larger impact forces can result in overuse injury
and mechanical fatigue at the joints of the lower limbs and
in the spine.
The shock absorption capabilities of the heel pad
can be enhanced by wearing footwear that has a heel counter
that confines the heel pad and by placing a shock absorbing
material or device (such as an air system, liquid system,
and valve system) under the heel to absorb impact energy
generated at heel strike and thereby reduce the magnitude
of the impact force. The effectiveness of known systems
varies considerably. Moreover, in many instances, known
systems require the addition of components to a
conventional article of footwear and therefore increase the
material costs and make more difficult the manufacture of
the footwear.
An object of the present invention is to provide
an article of footwear which is capable of minimising
impact shock.
According to the present invention there is
provided an article of footwear comprising:
(a) an insole having an upper surface, a lower
surface, and an opening; and
(b) a sole element secured to the lower surface
of the insole and extending through the
opening in the insole to project to or
above the upper surface of the insole to
form a load transfer region for
transferring load between a foot of a
wearer of the footwear and the sole
element, and the sole element comprising a
material capable of absorbing impact
energy.
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The present invention is based on the realisation
that the above construction of the sole element optimises
absorption of energy at impact and thereby minimises impact
force and impact shock. without wishing to be bound by a
particular theory, the applicant believes that this
substantial advantage of the footwear is achieved because
there is direct load transfer between the foot and the sole
element which avoids or minimises interference to load
transfer caused by the insole.
It is preferred that the sole element extend
through the opening in the insole to project above the
upper surface of the insole.
It is preferred, although not essential, that the
load transfer region be dome-shaped.
The opening in the insole may be of any suitable
shape.
The opening in the insole may be in any suitable
location.
it is preferred that the opening in the insole be
in the heel section of the footwear.
The footwear may comprise more than one opening
in the insole.
It is preferred that the sole element be secured
to the lower surface of the insole by moulding the sole
element onto the lower surface.
It is preferred that the sole element comprises a
midsole and that the footwear further comprises an outsole
secured to the midsole.
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Alternatively, in a situation where the footwear
does not include a midsole, the sole element may comprise
the outsole only.
It is preferred that the impact energy absorbing
material be a resilient material.
It is preferred particularly that the impact
energy absorbing material be selected from the group
comprising polyurethane rubber (natural or synthetic), PVC,
and any other suitable polymeric material.
It is preferred more particularly that the impact
energy absorbing material be expanded polyurethane.
It is preferred that the footwear further
comprises a member that extends across the opening and is
secured to the upper surface of the insole.
It is preferred that the member be a barrier.
It is preferred particularly that the barrier
member be a membrane.
It is preferred more particularly that the
membrane be flexible.
it is preferred that the sole element extend
through the opening in the insole and be secured to the
upper surface of the insole in the region of the opening.
it is preferred that the footwear further
comprises a reinforcing/stiffening member embedded in the
sole member in the region of the opening in the insole.
It is preferred that the reinforcing/stiffening
member extends transversely to the plane of the insole.
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it is preferred that the opening in the insole be
formed by cutting the insole to form a flap and thereafter
bending the flap downwardly from the plane of the insole.
It is preferred that the footwear further
comprises an upper secured to the insole.
According to the present invention there is also
provided a method of manufacturing an article of footwear,
the footwear comprising an insole, an upper secured to the
insole, and a sole element moulded to the insole, the upper
comprising toe, side, and heel sections, and the sole
element being formed from a material capable of absorbing
impact energy, the method comprising the following steps:
(a) cutting a section of the insole to form a
flap which is integrally connected to the
insole - without displacing the flap from
the plane of the insole;
(b) securing the upper to the insole;
(c) displacing the flap from the plane of the
insole so that the flap extends downwardly
transversely to the plane of the insole,
thereby to form an opening in the insole;
and
(d) securing the sole element to a lower
surface of the insole so that the flap
extends into the sole element and the sole
element extends through the opening to
project to or above an upper surface of the
insole to form a load transfer region for
transferring load between a foot of the
wearer of the footwear and the sole
element, and the sole element comprising a
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material capable of absorbing impact
energy.
The applicant has found that the above-described
method is particularly advantageous because it enables the
footwear to be manufactured on conventional equipment and
avoids substantial capital expenditure for new equipment
and/or modifications to existing equipment.
It is preferred that step (b) comprises:
(i) securing the toe section of the upper to
the insole in a toe lasting machine; and
(ii) securing the side and heel sections of the
upper to the insole in a side and heel
lasting machine.
It is preferred that step (d) comprises securing
the sole element by moulding the sole element to the
insole.
In a situation where the sole element is moulded
onto the insole, it is preferred that the method further
comprises a step between steps (a) and (b) of securing a
barrier member to an upper surface of the insole to extend
across the flap. The purpose of the barrier member is to
limit the penetration of sole material through the opening
in the insole during the moulding step.
It is preferred that the sole element be a
midsole and that the method further comprises moulding an
outsole to the midsole.
According to the present invention there is also
provided an insole for an article of footwear, the insole
comprising an upper surface, a lower surface, and an
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opening for receiving a section of a sole element formed
from a material capable of absorbing impact energy so that
the section forms a load transfer region projecting to or
above the upper surface of the insole.
It is preferred that the opening be formed by
cutting out a section of the insole to form a flap that is
integrally connected to the insole and can be displaced
from the plane of the insole to form a reinforcing/
stiffening member.
According to the present invention there is also
provided a sole unit for an article of footwear, the sole
unit comprising :
(a) an insole having an upper surface, a lower
surface, and an opening; and
(b) a sole element comprising a material
capable of absorbing impact energy secured
to the lower surface of the insole and
extending through the opening in the insole
to project to or above the upper surface of
the insole to form a load transfer region
for transferring load between a foot of a
wearer of the footwear (when constructed)
and the sole element.
The present invention is described further by way
of example with reference to the accompanying drawings in
which:
Figure 1 is a partially cut-away perspective view
of an article of footwear formed in accordance with one
preferred embodiment of the present invention;
Figure 2 is a cross-section along the line 2-2 of
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Figure 1;
Figure 3 is a top plan view of a heel section of
the insole;
Figure 4 is a cross-section along the line 4-4 of
Figure 1; and
Figure 5 is a cross-section similar to that shown
in Figure 2 which illustrates another preferred embodiment
of an article of footwear in accordance with the present
invention.
The article of footwear shown in Figures 1 to 4
comprises an insole 3, an upper 5 having an upper margin 29
that is wrapped over the edge of the insole 3 and secured
to a lower surface 11 of the insole 3, a midsole 9 moulded
to the lower surface 11 of the insole 3 and to the upper
margin 29, and an outsole 13 (which defines a tread of the
footwear) moulded to the midsole 9.
The midsole 9 is formed at least in part from a
material that is capable of absorbing impact energy, such
as expanded polyurethane or any other suitable resilient
material.
The midsole 9 and the outsole 13 may be of dual
density with, by way of example, the midsole 9 being made
from expanded polyurethane of specific gravity of the order
of 0.6 gm/cc which forms a cushion layer, and the outsole
13 being made from polyurethane of specific gravity of the
order of 1 gm/cc which forms a relatively tough outer skin.
Alternatively, the midsole 9 and the outsole 13 may be of
single density.
The insole 3 is formed with an opening 15 in the
heel section, and the midsole 9 extends through the opening
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15 and projects above the upper surface 7 of the insole 3
to form a generally dome-shaped load transfer region 31 for
transferring load between a heel of the wearer of the
footwear and the midsole 9 when the footwear contacts the
ground.
In this connection, the applicant has found that
this arrangement of the opening 15 and the midsole 9
optimises absorption of energy at impact and thereby
minimises impact shock. it is believed by the applicant
that this substantial advantage of the footwear is achieved
because there is direct load transfer via the load transfer
region 31 between the foot and the midsole 9 which avoids
or at least minimises interference to load transfer by the
insole 3.
Another advantage of the arrangement of the
opening 15 and the midsole 9 is that it does not involve
components, such as the prior art gel filled capsules, air
cavities and valving arrangements, that may fail in
service. In addition to this simplicity of construction,
the inherent strength and reliability of the footwear of
the present invention also stems from the fact that in its
preferred form the invention comprises a homogeneous unit
in which all of the components are bonded together. Thus,
there is not only an absence of complex components but also
"voids" and unbonded joints and boundary layers that result
from the inclusion of these components in footwear.
A further advantage of the arrangement of the
opening 15 and the midsole 9 is that, in accordance with a
preferred embodiment of a method of manufacture in
accordance with the present invention, the footwear may be
manufactured using conventional toe lasting machines and
side and heel lasting machines and therefore substantial
expenditure on new equipment or on modifications of
existing equipment is not required in order to manufacture
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the footwear. It is noted that the present invention is
not limited to this method of manufacture and the footwear
may be manufactured with any suitable technology including,
but not limited to: strobel stitched/slip lasting; string
lasting; stitch down/Veltschoen; Goodyear welt; and
cemented or stitched unit soles.
With particular reference to Figures 2 and 3, the
opening 15 is formed by die-cutting the insole 3 to form a
flap 23 having parallel sides 25 and a curved terminal end
27 and by bending the flap 23 downwardly at the junction
between the flap 23 and the insole 23 so that it extends
transversely to the plane of the insole 3 and extends into
the midsole 9.
The flap 23 has a number of important functions.
Firstly, the flap 23 acts as a reinforcement/stiffener of
the midsole 9. In particular, this feature improves the
torsional stability of the footwear and responds as a
spring "hinge". Secondly, the flap 23 forms a barrier to
inhibit penetration of sharp objects through the opening 15
into the foot of a wearer of the footwear. Thirdly, the
flap 23 assists in manufacture of the footwear in
accordance with a preferred method that is described below.
With reference to Figure 5, in the preferred
embodiment shown in that Figure the flap 23 is of a similar
construction to the arrangement shown in Figures 2 and 3,
save that the flap 23 is bent downwardly a greater angle to
the plane of the insole 3 than the arrangement shown in
Figures 2 and 3 and, in order to accommodate the flap 23 is
in the midsole 9, the flap 23 is bent upwardly mid-way
along its length. As a consequence, the flap 23 has a
steeply inclined inner section 23a and a less steeply
inclined outer section 23b.
A particular advantage of the embodiment shown in
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Figure 5 is that the flap 23 is displaced further away from
the opening 25 than the arrangement shown in Figures 2 and
3 and thereby minimises interference of.the flap 23 in the
forming of the load transfer regions 31.
With further reference to the Figures, the
footwear further comprises a flexible membrane 17 that
extends across the opening 15 and is secured to the upper
surface 9 of the insole 3. As is described in more detail
hereinafter, the principal purpose of the membrane 17 is to
form a barrier to limit the flow of midsole material
through the opening 15 and thereby to control the shape of
the load transfer region 31 during moulding of the midsole
9 onto the insole 3 in accordance with the preferred method
of manuf acture .
The membrane 17 is secured to the upper surface 7
of the insole 3 so that there is a section 21 of the upper
surface 7 (Figures 2 and 4) that separates the edge of the
opening 15 and the region of contact between the membrane
17 and the insole 3. The midsole 9 extends across and is
secured to this section 21 of the upper surface 7. This
feature further improves the performance of the footwear.
Furthermore, the opening 15 comprises a
radiussed edge (not shown) which in the preferred method
assists in the flow of midsole material through the opening
15 during moulding of the midsole 9 onto the insole 3 in
accordance with the preferred method of manufacture.
The preferred method of manufacture of the
footwear comprises a first step of die-cutting the flap 23
in the insole 3 and thereafter securing the membrane 17 to
the upper surface 7 of the insole 3.
The assembly of the insole 3 and the membrane 17,
with the flap 23 in the plane of the insole 3, is then
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positioned on a conventional toe lasting machine (not
shown) and the machine is operated to secure the toe
section of an upper 5 to the lower surface 11 of the insole
3. The assembly is then transferred to a conventional side
and heel lasting machine (not shown) and the machine is
operated to secure the side and heel sections of the upper
5 to the lower surface 11 of the insole 3.
It is noted that an important requirement of
conventional lasting machines is that an insole be
sufficiently rigid to act as a stable base. The applicant
has found that the above-described assembly of the insole
3/flap 23/membrane 17 has sufficient rigidity and therefore
can be used without difficultly on conventional lasting
machines.
After the upper 5 is secured to the insole 3, the
flap 23 is displaced downwardly away from the plane of the
insole 3 to form the opening 15. Thereafter, the assembly
of the upper 5/insole 3 is positioned on a conventional
injection moulding machine (not shown) and the machine
injects outsole material into a cavity in the bottom of the
mould assembly to form the outsole 13.
The final step of the method comprises injecting
midsole material into the space between the upper 5/insole
3 assembly and the outsole 13.
In order to investigate the performance of the
footwear of the present invention the applicant retained
the School of Human Biosciences, Faculty of Health
Sciences, LaTrobe University, Victoria, Australia to carry
out a study on the preferred embodiment of footwear in
accordance with the present invention having the bent flap
23 as shown in Figure 2.
in the study the heel strike transient of the
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ground reaction force (GRF) was measured as subjects walked
over a force plate. The acceleration transient propagated
to the tibia, while walking, was measured using an
accelerometer. The effectiveness in reducing the GRF and
tibial acceleration transients was measured relative to a
standard article of footwear. Lace-up and elastic sided
styles of footwear were tested. The heels were also
statically tested by striking them with a pendulum (hammer)
and observing the acceleration transient transmitted
through the heel.
METHOD
Static Impact Tests
Static impact tests were performed by allowing a
hammer-shaped pendulum to strike footwear on the lateral,
posterior region of the heel. The pendulum was mounted in
a frame that was secured to the test bench. The pendulum
was 0.94 m in length and had a mass of 3.65 kg, the
cylindrical striking-head of the pendulum was 0.087 m long
and 0.045 m in diameter with a mass of 1 kg. Footwear was
mounted on a suitably sized SACH prosthetic foot (1D20 Otto
Bock Dynamic Pro) attached to a 0.13 m long trans-tibial
pylon (Otto Bock tube adaptor). A thin nylon sock was
placed over the foot to reduce friction between the leather
footwear and the rubber foot. The pylon was affixed to a
rigid mounting frame secured to the test bench. An
accelerometer (Kulite GY125-10) was mounted on the pylon,
midway along its length, to measure the acceleration
transients due to the shock of impact transmitted
longitudinally along the pylon. The point of impact on the
heel was positioned at the equilibrium position of the
striking-head of the pendulum. The pendulum was displaced
400 from its equilibrium position and held in a release
mechanism, upon release it was allowed to fall freely to
strike the heel.
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The accelerometer was supplied with an excitation
voltage of 15 V dc from a regulated power supply (Tektronix
PS501-1). The accelerometer output was amplified by a
differential amplifier (Tektronix AM502) using a 300 Hz low
pass filter. Output from the amplifier was sampled at a
rate of 1 kHz by an A-D converter (Maclab/4 controlled by
Scope v3.2.6 and a Macintosh Classic computer). Shock of
impact was then quantified from the output record by
measuring the magnitude of the first negative peak after
impact. A reduction in magnitude indicated increased shock
absorption by the heel of the footwear. Five impact tests
were performed on each article of footwear.
Four types of footwear were tested, namely:
(i) conventional footwear - lace-up,
(ii) the preferred embodiment footwear - lace-
up,
(iii) conventional footwear - elastic-sided, and
(iv) the preferred embodiment footwear -
elastic-sided.
There were six pairs of each type of footwear,
with two pairs each of sizes 7, 8, and 9. A total of 48
articles of footwear were tested. Footwear size was
determined by the foot size of each subject for the dynamic
impact tests, otherwise footwear was selected at random
from stock held by the applicant.
Dynamic Impact Tests
Six subjects donned footwear for the dynamic
testing. All subjects were in good health and had no
history of lower limb pathologies. Five of the subjects
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were male, and one female. Average age, stature and mass
were 36 years, 1.778 m and 78.8 kg respectively (Table 1).
Two of the subjects wore size 7 footwear, another two wore
size 8 and the final two wore size 9.
Table 1. Body mass, stature, age and gender
for the six subjects participating in
the dynamic trials.
Subject Body Stature Age Gender Boot
mass (a) (years) size
(kQ)
1 75.5 1.730 23 F 7
2 69.3 1.655 48 M 7
3 92.2 1.850 21 M 9
4 78.3 1.830 47 M 8
5 83.7 1.800 35 M 9
6 73.6 1.805 40 M 8
Each subject was instructed to walk at a constant
cadence down a 10 m walkway. Cadence was regulated by
having the subjects synchronise their steps with the beat
of a metronome cadences of 100 and 120 steps/min were used.
Each subject performed a total of 40 trials with
each of the 4 footwear types. At least 2 days separated
the testing of each footwear type to allow the subjects to
acclimatise to wearing a footwear type.
For each footwear type 10 trials using the force
plate were performed at each of the cadences (100 and 120
steps/min). The vertical component of the ground reaction
force (Fs) was measured by a force plate (Kistler 9281B
force plate) mounted flush with the floor in the walkway.
Each subject started walking at a distance of approximately
6 m from the force plate. The starting position was set so
that the subject contacted the force plate with their right
foot.
Also, for each footwear type 10 trials using the
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accelerometer were performed at each cadence. Acceleration
transients transmitted longitudinally along the tibia after
the heel strike were measured using an accelerometer
(Kulite GY125-10) that was firmly secured madially and
proximally to the anterior of the right tibia (tibial
flare). Accelerometer output was recorded for the step
where the foot struck the force plate.
The force platform output was amplified (Kistler
5007 Y15 charge amplifiers, Kistler 5217 summing
amplifiers, Kistler 5215 Y12 analogue divider and Kistler
5675 central control unit) and sampled at a rate of 1 kHz
by an A-D converter (Maclab/8 controlled by Scope v3.2.6
and a Macintosh LC475 computer). The F. output exhibited a
heel strike transient after heel contact, and the transient
resulted in impact force peaks Fl and Fz.
For this study the magnitude of the first impact
force peak (Fai) and the time (At) from heel contact to
this peak were measured. The impact force rate (FRZi) was
then calculated by
FRzi = Fzi/At.
The accelerometer used to measure acceleration
transients transmitted to the tibia after heel strike was
supplied with an excitation voltage of 15 v dc from the
regulated power supply (Tektronix PS501-1). The
accelerometer output was amplified by a differential
amplifier (Tektronix AM502) using a 300 Hz low pass filter.
Output from the amplifier was sampled at a rate of 1 kHz by
an A-D converter (Maclab/8 controlled by Scope v3.2.6 and a
Macintosh LC475 computer). Shock transmitted to the tibia
after heel strike was then quantified from the output
record by measuring the magnitude of the first positive
peak after heel strike. This is commonly referred to as
the initial peak tibial acceleration (IPA). A reduction in
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magnitude indicated increased shock absorption by the heel
of the f ootwear .
Statistical Analysis
For the static impact testing a 2 group unpaired
Student's t test was performed to compare the initial peak
acceleration transmitted through the 24 articles of
footwear with the conventional heel and the 24 preferred
embodiments.
For the statistical analysis of the dynamic data
a series of planned comparisons was performed in which
paired t tests were used to compare the parameters recorded
from the subjects when wearing the conventional footwear
with those measurements taken when wearing the preferred
embodiments. To compensate for accumulation of family wise
error due to multiple comparisons, a Bonferroni adjustment
was made and the significant levels for the comparisons
altered accordingly.
RESULTS
The mean initial peak acceleration in response to
the impact of the 24 conventional articles of footwear was
3.450 g (Std. Dev., 0.244).
The mean initial peak acceleration in response to
the impact of the 24 preferred embodiments was 3.035 g
(Std. Dev., 0.267).
The difference between the means, which amounts
to 12.0% less peak acceleration in the preferred
embodiments than in the conventional footwear, was
significant (t=11.9, p<.0001).
The mean values for the 3 shock paranneters
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measured during the dynamic trials when subjects wore the
preferred embodiments are shown in Table 2.
Table 2. Mean values of shock measurements for
all subjects wearing preferred
embodiments.
All lace- Lace-up All Elastic
up fast Elastic fast
IPA (g) 1.762 1.928 1.780 2.039
F=i (N/kg) 5.189 5.860 4.788 5.994
FRai (N/kg.s) 129.39 149.50 119.85 142.83
"All Lace-up" and "All Elastic" columns combine the data take from all
subjects walking at both speeds in lace-up boots and elastic sided boots
respectively. "Lace-up fast" and "Elastic fast" columns contain data
obtained when walking at the higher speed only.
The values for elastic and lace-up boots are
similar with no significant differences within conditions.
As would be expected the values for the shock parameters
increased with increased walking speed.
The 3 shock parameters measured during the
dynamic trials were significantly lower for the group of
subjects when walking in the preferred embodiments than
when walking in the conventional articles of footwear. The
differences are summarised in Table 3.
Table 3. Percentage decrease in shock
measurements of preferred embodiments
compared to conventional footwear
worn by all subjects.
All Lace- Lace-up All Elastic
up fast Elastic fast
IPA 26.8 32.8 22.5 22.5
Fsi 10 . 0 r 9.1'' 6.3 7. 8~
FRzi 19.5 19.3 11.8 15.5
"All Lace-up" and "All elastic" columns combine the data taken from all
subjects walking at both speeds in lace-up boots and elastic sided boots,
respectively. "Lace-up fast" and "elastic fast" columns contain data
obtained when walking at the higher speed only. All values are
significant at p<.001 except' p<.005, Ap<.05 after Bonferroni adjustment.
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The values shown in Table 3 are the mean for all
trials from all subjects tested and generally show a large
difference between heels.
Despite these large, significant differences for
the group there was a variation between individuals. For
some subjects there were only small differences between
parameters when wearing footwear with the different heels.
For others, who tended to have a higher impact
acceleration, the mean differences were large and could be
as high as 50%. There was a strong positive correlation
between the magnitude of IPA and the difference in shock
between heels. A regression analysis was performed in
which the mean difference in IPA for each subject when
wearing preferred embodiments and conventional footwear was
correlated with the individual's mean IPA in conventional
footwear. Linear regression yielded a coefficient of
determination (r2) of 0.657 (p=0.0014) indicating that 66%
of the inter-subject variation in the mean difference
between the shock absorbing capacity of the two heels could
be accounted for by the magnitude of the impact
acceleration.
DISCQSSION
The study provided objective measurements of the
shock absorbing capacity of the conventional footwear and
the preferred embodiments both in controlled static bench
tests and in conditions typical of normal use.
The significant reductions in all shock
parameters in both the static and dynamic testing clearly
indicated that preferred embodiments had superior shock
absorbing capacity than the conventional footwear and, on
average, provided superior cushioning while subjects
walked.
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Of the shock related parameters used in the
study, IPA and FR=i are generally better monitors of
changes in shock absorption than is F,i when people walk in
shoes. Fzi indicates only the magnitude of the impact
force of the heel strike transient and does not take into
account the rate at which force increases. As indicated
above, wearing appropriate footwear markedly reduces the
magnitude of the impact when compared to walking in bare
feet. it is theoretically possible that F,i could be
higher when wearing certain footwear yet have increased
shock absorption because of a slower rate of force
increase. In the study it was found that F,i for subjects
wearing the preferred embodiments was significantly less
than when wearing the conventional footwear. The decrease
in FRz1 when wearing the preferred embodiments was
proportionally greater than the decrease in F,i which may
indicate that the superiority of the shock absorbing
properties of the preferred embodiments relates to reducing
both the magnitude of the impact force and the rate at
which the force increases.
The group of subjects used in the study provided
a range of heights, weights, shoe size and walking styles
which suggest the results of the dynamic tests would
generalise to a large proportion of the adult population.
There was a tendency for the superiority in shock
absorption with the preferred embodiments to be greater
when higher transient peak accelerations occurred either
due to the nature of an individual's walking
characteristics or, within subjects, due to an increased
walking speed. These observations suggest that the
advantage of the preferred embodiments increased as larger
acceleration transients are applied to the leg. Higher
acceleration transients may occur when carrying a load and
in many other physical activities where the normal walking
style is altered.
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Many modifications may be made to the preferred
embodiment of the present invention described above without
departing from the spirit and scope of the invention.
For example, whilst the opening 15 is located in
a heel section of the preferred embodiment of the footwear
shown in the figures it can readily be appreciated that the
present invention is not restricted to this arrangement and
the opening 15 may be positioned in any required section of
the footwear.
In addition, it can readily be appreciated that
the footwear may include more than one such openings 15.
In addition, whilst the preferred embodiment
comprises a generally dome-shaped load transfer region 31,
it can readily be appreciated that the present invention is
not restricted to this arrangement and the load transfer
region 31 may be of any suitable shape.
In addition, whilst the preferred embodiment of
the footwear shown in the figures comprises a flap 23 cut-
out from the insole 3, it can readily be appreciated that
the present invention is not restricted to this
arrangement. For example, the flap 23 may be separate from
the insole 3 and formed from a different material from that
of the insole 3. Furthermore, the flap 23 may be of a
shape that is different to that of the opening 15 and/or
located in any suitable orientation, ie. at a range of
angles and different planes, to optimise the performance of
the flap 23.
Furthermore, whilst the above description in
relation to the drawings is in the context of a completed
article of footwear, it can readily be appreciated that the
present invention is not so limited and extends to the
insole element per se and to a sole unit comprising the
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insole and the sole element formed from a material capable
of absorbing impact energy secured to the insole.
