Comparison of Abdominal Muscle and Subcutaneous Fat Thickness and Core Stability between Normal Weight Non-Obesity, Normal Weight Obesity, and Obesity Groups in Young Korean Women

Background: We compared abdominal muscle and subcutaneous fat thicknesses, and core stability among young Korean women with normal weight non-obesity (NWNO), normal weight obesity (NWO), and obesity (OB). Methods: Between May and September 2024, fifty-seven female university students from K University in Gwangju, Republic of Korea, were classified into three groups (NWNO: n = 15, NWO: n = 20, and OB: n = 22) based on body mass index and body fat percentage. The thicknesses of the abdominal muscles, including the transverse abdominis (TrA), internal abdominal oblique (IO), and external abdominal oblique (EO) muscles, and of the subcutaneous fat were measured using real-time ultrasound imaging. Core stability was assessed using trunk extensor, trunk flexor, and side-bridge endurance tests. Data were analyzed using one-way ANOVA with a significance level of 0.05. Results: Significant differences were observed in the thicknesses of the TrA (P = 0.002), EO (P = 0.001), and subcutaneous fat (P < 0.05) between groups. The OB group had the greatest TrA and subcutaneous fat thicknesses. The side-bridge endurance test revealed a significant difference in core stability (P = 0.002), with the OB group demonstrating the lowest core stability. Conclusion: Although the OB group had the largest muscle thickness, it demonstrated lower core stability than the NWNO group. These results suggest that obesity might impair neuromuscular activation and muscle fiber recruitment, leading to functional limitations despite increased muscle mass. These findings emphasize the importance of preventing and managing normal-weight obesity in women in their 20s.