[Purpose] The aim of this study was to determine the appropriate pressure variation for
performing a successful abdominal drawing-in maneuver (ADIM). The abdominal muscle
thickness variations and contraction ratios were examined in relation to pressure
variations using a Pressure Biofeedback Unit (PBU) during an ADIM in the supine position.
[Methods] The PBU was placed identically between the lumbar lordosis of 20 healthy
subjects (12 males and 8 females) and the pressure of the PBU was maintained at 40 mmHg.
Then, while the subjects performed ADIM at four random pressure variations (0, 2, 4, or 6
mmHg), the thicknesses of the transversus abdominis (TrA), the internal oblique abdominal
muscle (IO), and the external oblique abdominal muscle (EO) were measured using
ultrasonography. [Results] Pressure increases of 0–2 mmHg resulted in significant
decreases in IO and EO thicknesses compared to pressure increases of 6 mmHg. Increases of
0–2 mmHg also resulted in significant decreases in IO+EO and EO contraction ratios
compared to pressure increases of 6 mmHg, while the preferential activation ratio of the
TrA was significantly increased. [Conclusion] Compared to the other pressure increases, an
increase of 0–2 mmHg effectively regulated the thicknesses and contraction ratios of
superficial muscles such as IO and EO, rather than the thickness and contraction ratio of
the TrA, showing high and indirect preferential activation ratios for TrA. Therefore, for
successful ADIM, rather than using large PBU pressure increases, exercises that promote
slight increases of around 0–2 mmHg from a baseline of 40 mmHg are desirable.