Core stability mediated by the abdominal draw-in maneuver (ADIM) has been proven to be an important component of neuromuscular motor control before movement. However, no previous research has investigated which position is best for performing ADIM to achieve optimal core stability. This study aimed to define the effectiveness of performing ADIM in three different positions (prone, supine, and hook lying) on abdominal muscle thickness in nonsymptomatic participants. In total, 30 nonsymptomatic participants (mean age: [Formula: see text] years) were randomly assigned to a trial sequence using the random sequence method. The clinical outcomes were transverse abdominis (TrA), external oblique (EO), and internal oblique (IO) muscle thicknesses, which were evaluated using ultrasonography (US) and muscle thickness balance ratio. One-way repeated-measures analysis of variance (ANOVA) was used to evaluate the US data to determine if the resulting TrA, IO, and EO muscle thicknesses from the three different positions were statistically significant. Bonferroni correction was used as a post hoc test if statistical significance was found. The [Formula: see text] value was set to 0.013. One-way ANOVA showed a significant difference in the thickness of the TrA, IO, and EO muscles resulting from the different positions ([Formula: see text]). Post hoc analysis using Bonferroni correction revealed that the prone position resulted in greater changes than the supine and hook-lying positions ([Formula: see text], respectively). ANOVA did not show a significant change in the TrA, IO, and EO muscle thickness balance ratios ([Formula: see text], 0.44, and 0.59, respectively). The results provide innovative clinical evidence that performing ADIM in different positions (prone, supine, and hook lying) has different effects on abdominal muscle thickness in nonsymptomatic participants.