[Purpose] The purpose of this study was to investigate the effective strength levels of
abdominal muscle contraction using the bracing contraction method. [Subjects] The
experiment was conducted with 31 healthy male (M=15) and female (F=16) adults attending D
University in Busan; all participants had less than obesity level BMI (BMI<30).
[Methods] Bracing contraction was performed by the subjects in the hook-lying position at
maximum and minimum pressure levels, five times each, using a Pressure Biofeedback Unit
(PBU), and the mean measurement value was calculated. The maximum pressure level was set
at 100% and the half maximum pressure level was set at 50%. Each subject’s left and right
abdominal muscle thicknesses were then measured by ultrasound imaging in each state: at
rest, 100% contraction, and 50% contraction. [Results] No significant differences were
found between the left and right sides of the transversus abdominis (TrA) at rest, 50%, or
100% contraction. The external oblique abdominis (EO) and internal oblique abdominis (IO)
showed no significant difference at rest or at the 50% contraction. However, a significant
difference was noted at 100% contraction for the EO and IO. [Conclusion] Application of
abdominal contraction using bracing can achieve symmetry in the left and right abdominal
muscles at less than the maximum contractile strength. The occurrence of asymmetry in the
left and right abdominal muscles at the maximum contractile strength suggests that the
most suitable contractile strength in this exercise is less than the maximum contractile
strength.