Abdominal muscle thicknesses
An Aplio™ 500 ultrasound machine (Toshiba, Tokyo, Japan) with a 12 MHz
linear probe was used to examine the abdominal musculature (set to scan
at a depth of 6 cm with a frequency for musculoskeletal exploration).
All images were obtained with subjects relaxed at the end of expiratory
movements (Supplementary Figure S1) . The lateral abdominal
musculature (TrA, IO and EO) was examined following a previously
described protocol adapted for use with pregnant
women4. Subjects adopted the supine decubitus position
with a foam roller under the knee joint to ensure that the legs were
flexed (hip at 30º); a pillow was placed under the head to facilitate
relaxation of the abdominal musculature. The probe was placed between
the iliac crest and the last rib in the mid-axillary line. Measurements
were taken 1 cm from the insertion edge of the transverse fascia - one
at rest and one during activation (for which the subject was instructed
to make the movement for pulling up a vaginal tampon with the perineal
musculature). The mean muscle thicknesses on each side were then
determined and overall means calculated.
The IRD was measured with the subject in the same position. The probe
was placed transversely across the midline of the abdomen, 2 cm above
the umbilicus. Measurements were taken at rest and during activation,
for which the subject performed a gentle crunch lasting about 3-5 s. The
position for taking the measurement was marked on the skin to
standardize the position of the probe. Since there is no consensus
regarding the cut-off point for diastasis recti in pregnant
women2,18,19, subjects were classified as above or
below the 50th percentile (i.e., median) of the IRD,
both at rest and during crunches.