BIOMECHANICAL ANALYSIS OF OBESE AND NON-OBESE
CHILDEREN PLANTAR PRESSURE
ABSTRACT
This study examined the effects of obesity on dynamic plantar pressure distributions in
children. Experimental data on body mass index (BMI) and plantar pressures were collected
for 15 obese children and 15 no obese children. 15 obese (age 9.8+/-2.0 y, BMI 25.8+/-3.8 kg
m(-2)) children matched to 15 no obese children (age 9.9+/-2.1 y, BMI 16.8+/-2.0 kg m(-2)),
for gender, age and height. Right and left foot plantar pressures were obtained using an Foot
scan platform and foot scan software are used for plantar pressure measurements to calculate
the peak force and pressure experienced under area of each child’s feet during dynamic
conditions. These variables were measured under ten regions of interest in each foot print:
Lateral heel, Medial heel, Midfoot, Metatarsal 5, Metatarsal 4, Metatarsal 3, Metatarsal 2,
Metatarsal 1, Toes2-5, Toe1.Descriptive statistics and one-way analysis with stepwise were
used to analyze the data. while walking, the obese children generated significantly higher
forces over all areas of their feet, except the toes. Despite distributing these higher forces over
a significantly larger foot area when walking, the obese children experienced significantly
higher plantar pressures in the midfoot and under the second to fifth metatarsal heads
compared to the no obese children. The greatest effect of body weight on higher peak pressure
in the obese was found under the longitudinal arc of the foot and under the metatarsal. Further
studies are needed to investigate the structural and functional characteristics of children's feet.
Keywords: Obesity, Footscan Platform, Plantar Pressure
INTRODUCTION
Obesity is a condition characterized by the build up of excessive body fat.
Obesity is defined differently depending on the country, but in Western
countries, such as the U.S. and many European countries, obesity is defined as a
body mass index (BMI) of 30 kg/m^2.
A BMI is calculated by taking a person's weight (in kilograms) and dividing it by
the square of their height (in meters). Using the BMI, doctors may classify
someone as underweight, normal weight, overweight, or obese.
Each time the foot contacts the ground during walking, peak vertical ground
reaction forces typically reaching 120% of body weight are generated.1 It has been
estimated that an individual with a mass of 67 kg, walking 1.6 km, would be
required to absorb 64.5 tonnes on each foot.2, 3 Considering the need to consistently
withstand such high loading, it is not surprising that foot discomfort, pain and
pathologies frequently occur. These foot pathologies may be exacerbated in obese
or overweight individuals due to increased mechanical loading of the feet caused by
their additional mass.4, 5, 6, 7
Knowledge concerning the stance and gait of obese individuals generally begins with
subjective clinical assessments, based on the detection of their serious difficulty in performing
activities of daily life, especially locomotion. Therefore, urgent attention must be given to the
physical consequences of repetitive overload, mainly in the lower limbs, in order to provide
support in the areas of prevention, treatment, and obesity control1. The assessment of plantar
pressure distribution represents an important clinical tool for understanding the structural
andfunctional implications of obesity.The influence of body mass on the plantar pressure
variables is not yet clear. Therefore, it becomes necessary to comprehend the main effects of
obesity on the biomechanical characteristics of gait, as well as on the movement of the feet,
which can contribute to understanding how obesity influences weight-support activities.
Hence, the objective of this study was to determine dynamic plantar pressure distribution
between obese and nonobese children and correlate body mass.
MATERIAL AND METHODS
In this study, 30 healthy male subjects were enrolled: 15 obese childeren , 15non-obese
childeren (see Table 1). The mean age of the obese group was 9,8 years, and that of the nonobese group
was 9,9 years. The obese group BMI was bigger than nonobese BMI. (Table 1).Obese children vas significant
tan nonobese children in BMI.
Table 1: Demographics of obese and nonobese childeren
Obese(N:15)
Non-obese(N:15)
Age(years)
9.8+/-2.0 years
BMI
25.8+/-3.8 kg m(-2)
9,9+/-2.1 years
P value
NS
16.8+/-2.0 kg m(-2)
P<.05
Plantar pressure data were collected from all subjects. A footscan® plate system (RsScan nv.,
2m x 0.4m, 16384 sensors, 500 Hz, dynamic calibration with footscan® plate system) was
mounted in the middle of a 8 m long track. The subjects walked barefoot at their own pace. All
measurements were taken with the subjects walking barefoot over the plate. Three walks for
each foot (three walks for each subject) were recorded and printed. Each print consisted of a
time peak-pressure curve for ten regions of interest on the foot. The regions of interest, which
were analyzed automatically by the system software, were lateral heel, medial heel, midfoot,
lateral (Metatarsal 5, Metatarsal 4), central (Metatarsal 3, Metatarsal 2, Metatarsal 1) and the
toes 2-5, the toe 1(Figure1). The time variables were calculated as the ratio of time from the
start of the stance to peak pressure under the region of interest and the total stance time. The
pressure variables were calculated as the ratio of the peak pressure under the region of interest
to the body weight (Figure 2).
Figure 1 Representing of foot division into the 10 anatomical area
Fig. 2. Graphical presentation of plantar pressure of foot regions by RSscan
footscan® systems
Statistical Analysis
Means (SD) were calculated for the different time and force variables. The differences within
the groups and between the groups were compared using one way analysis of variance.
Differences of p<0.05 were considered significant.
RESULTS
Plantar Pressure Distributions
There was a significant delay to the time of peak Pressure under lateral forefoot (Meta5,
Meta4, Meta3), and toes in the obese childeren (Table 2). There was significantly longer
contact time of lateral heel in the obese childeren.
Table 2. Plantar Peak Pressure distribution of obese and nonobese childeren
Obese (N=15)
Lateral Heel
Medial Heel
Midfoot
Meta 5
Meta 4
Meta 3
Meta 2
Meta 1
Toes 2-5
Toe 1
Nonobese (N=10)
9.38(4.6)
11.28(1.6))
2.78 (1.1)
1.19 (2.4)
14.9 (3.1)
21.5(6.9)
18.7(5.1)
6.8(2.7)
0.0(0.0)
8.5(3.1)
9.15(4.1)
15.01(4.1)
0.18(0.8)
2.6(1.4)
5.3(2.4)
14.2(7.2)
9.651.6)
5.1(3.5)
0.43(0.4)
4.33(2.6)
p Values
NS
NS
NS
<0.05
<0.05
<0.05
NS
NS
NS
NS
Mean(SD); Newton/cm2; NS:No Significance P<0,05
The BMI value obtained for obese children (25.8 ± 3.8 kg/m2) was significantly higher
(p<0.01) than non children (16.8+/-2.0 kg/m2).
During walking, the Obese children showed greater contact areas than the nonobese childeren
with significant differences in all areas of the foot (p < 0.01). As for peak pressure, the Obese
childeren showed greater values, being statistically different from the Non obese children in
all areas of the foot ( p < 0.05). For maximum mean pressure, there were differences in the
Metatarsal 3,Metatarsal 4,Metatarsal 5 forefoot areas, with greater values for the Obese
childeren. Table 2 represents the comparison between the two groups during gait.
DISCUSSION
The greater dynamic forces generated in the heel, midfoot and forefoot regions by
the obese children , were anticipated due to their greater body mass. It would
appear, however, that loads exerted on the toes (Toe1-5) are not affected by
increased body mass.
The obese children displayed a significantly increased foot contact area in nine out
of the 10 foot regions during gait, relative to the nonobese children. These findings
are consistent with the flatter, broader foot structure noted to be characteristic of
obese prepubescent children by Riddiford-Harland et al.8 This increased midfoot
contact area displayed by obese children during gait may simply be due to the
continued presence of a fat pad in this foot region that is no longer present in
normal mass children. Such a fat pad may be an adaptive response to assist obese
children cushion the higher forces associated with their increased mass or merely
another site of increased adiposity that has little functional significance.
Alternatively, this increased midfoot contact area may represent structural
deformity of the obese children's feet, indicative of collapsed longitudinal arches
and the foundation for future pathologies, caused by the need to continually bear
greater mass. As the mechanism of this increased midfoot contact area is purely
speculative, further research pertaining to the causes of increased midfoot contact
areas during gait in obese children is recommended.
Obese children in the present study generated significantly greater mean peak
pressures under the midfoot and second to fifth metatarsal heads, compared to their
nonobese counterparts. The increase in midfoot pressures displayed by the obese
children is likely a consequence of the obese children having flatter feet; the medial
midfoot region contacts the pressure platform, generating pressure readings in this
foot area. In contrast, few of the nonobese children's higher arched feet made
contact with the platform in the medial midfoot region, thereby resulting in the
lower pressures observed. As these increased pressures experienced by the obese
children in the medial midfoot area are relatively low compared to other areas of
the foot, they are not considered problematic.
Conversely, the peak pressures generated by the obese children for Metetarsal
3,Metetarsal 4 and Metetarsal 5 were high relative to other foot regions, as well as
being significantly higher than the plantar pressures generated by the nonobese
children . As these higher pressures are being experienced on smaller bony and
ligamentous structures surrounding the second to fifth metatarsal heads, this may
have negative consequences for the feet of obese child in terms of an increased risk
of forefoot pathologies, such as stress fractures of the metatarsal bones and
ulcerations, particularly in those obese children who progress to developing type II
diabetes.
Conclusion
Based on the findings of the present study it is postulated that obese children might be at an
increased risk of developing foot discomfort and/or foot pathologies, such as stress fractures
in the forefoot. it is recommended that the effects of obesity on the structural and functional
characteristics of children's feet be further investigated.
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