The correlation between physical features and body sway on standing upright was explored in women before and after
the delivery. Body sway during upright standing was recorded in 18 women in the third trimester and 1 month after delivery.
Height, body weight, body mass index (BMI), and abdominal circumference were also registered twice. In women
at the 38th week of gestation on standing upright, the abdominal circumference was positively correlated with the total
path length (LNG) and enveloped area (ENV-AREA) of body sway. The path length of body sway in antero-posterior axis
(Y-LNG) was also correlated with the abdominal circumference, but the path length in medio-lateral axis showed no such
correlation. These correlations were not observed at 1 month after delivery. The body weight and BMI did not correlate
with parameters of body sway either in the 3rd trimester or postpartum. Fast Fourier transform (FFT) analysis of body
sway showed that the percentile power of the frequency band of 1.0-10.0 Hz, stabilized by the somatosensory inputs,
was smaller in the 3rd trimester than that postpartum. It is hypothesized that the reliance on somatosensory information
for maintaining standing posture increases as the abdominal circumference increases during pregnancy.
In pregnant women, standing posture changes as the fetus develops.
Increasing load onto the lumbar spine and abdominal
muscles causes a shift of the head position in the posterior
direction and increases lumbar lordosis and anterior pelvic tilt. These changes in body alignment influence the stability
of standing posture. Indeed, an intervention in the USA
showed that almost 25% of employed women sustain a fall at
work during pregnancy. Stabilometric analyses of standing
posture have coincidentally shown that the area of body
sway increases during pregnancy. The path length of
antero-posterior body sway increases during pregnancy and
decreases between late trimester and postpartum. On
the other hand, the path length of body sway in medio-lateral
axis decreases or remains unchanged. Therefore, the increase
in sway area during pregnancy is mainly caused by the
increase in the path length of antero-posterior body swayWe have previously shown that the power of 1.0-10.0 Hz band
of body sway is smaller in pregnant women than that in nonpregnant
controls. Body sway of 1.0-10.0 Hz band is stabilized
by somatosensory inputs.
Therefore, we thought that
some changes in physical features during pregnancy would
increase the reliance on somatosensory inputs and help to
maintain the standing posture. Indeed, it has been reported
that body weight positively correlates with the antero-posterior
body sway in obese women on standing. The body
weight and fat mass increase as pregnancy proceeds. The
abdominal circumference also increases as the fetus develops.
Therefore, in the present experiments, we explored the correlation
between physical features such as body weight, body
mass index (BMI) and abdominal circumference, and parameters
of body sway during pregnancy employing a within-subject
paradigm. Fast Fourier transform (FFT) analysis of body
sway was also introduced in order to evaluate the rationale
contribution of sensory inputs to maintain the standing posture,
i.e., visual, somatosensory, and vestibular inputs. These
sensory inputs with different modalities influence the power
spectrum of body sway.
Participants were 18 women who gave birth at Yamanashi Red
Cross Hospital and Fujiyoshida Municipal Hospital, Yamanashi,
Japan. Ten women were primiparous and 8 were multiparous.
Data for the 3rd trimester were collected once after the obstetric
examination on a weekly basis, and data postpartum at
1 month after delivery (Table 1).All experimental procedures were performed in accordance
with the Ethics Committee of the Faculty of Nursing, Yamanashi
Prefectural University on the basis of the Declaration
of Helsinki, and informed consent of all participants was obtained
in written form.
Postural sway was recorded by detecting the body’s center
of gravity continuously with a force platform equipped with
a data processor (Gravicorder G-5500, Anima, Tokyo, Japan).
Participants were requested to stand on the platform with
their feet parallel, gazing at a target, a black circle with a diameter
of 12 cm on a white background, fixed at a 1.5 m distance
and at the height of the participant’s eyes. This arrangement
of the visual target provided a visual angle of 4.58 degrees.
The body sway of each participant was recorded for 1 min, first
with the eyes open and next with the eyes closed.
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