Background: Functional flatfoot induces medial longitudinal arch collapse and neuromuscular imbalance between intrinsic and extrinsic foot muscles. While targeted foot core training is a standard intervention, the influence of weight-bearing postures on the selective activation of these muscles remains biomechanically ambiguous. Objects: This study aimed to investigate the electromyographic (EMG) activity of the abductor hallucis (AH) and tibialis anterior (TA) under different weight-bearing conditions and specific foot core exercises in individuals with functional flatfoot. Methods: Thirty young adults with functional flatfoot participated in this cross-sectional study. Surface EMG was utilized to measure the muscle activity of the AH and TA during three exercises: short foot (SF), toe curl (TC), and toe spread (TS). Each exercise was performed under two weight-bearing conditions: non-weight-bearing (sitting) and full-weight-bearing (standing). A 2 × 3 repeated measures ANOVA was conducted to analyze the main effects and interactions. Results: The interaction effect between posture and exercise type was not statistically significant for either the AH (p = 0.145) or TA (p = 0.661). Furthermore, weight-bearing posture yielded no significant main effect on muscle activation. However, the type of exercise demonstrated a highly significant main effect (p < 0.001). Post-hoc analysis revealed that AH activation was significantly greater during SF and TS compared to TC (p = 0.002), with no significant difference between SF and TS. Conversely, TA activation was significantly higher during TC than during SF and TS (p < 0.001). Conclusion: Weight-bearing posture does not dictate the magnitude of foot muscle activation; rather, specific exercise kinematics drive selective neuromuscular recruitment. Clinicians can safely prescribe the SF and TS exercises in a seated position to optimally isolate the AH without inducing compensatory TA hyperactivation, thereby providing a secure and targeted rehabilitation strategy for flexible flatfoot.

INTRODUCTION
MATERIALS AND METHODS
    1. Study Design
    2. Sample Size Calculation
    3. Subjects
    4. Settings
    5. Measurement
    6. Experimental Procedures
    7. Statistical Analysis
RESULTS
    1. General Characteristics of the Subjects
    2. Comparison of Muscle Activation in the AbductorHallucis
    3. Comparison of Muscle Activation in the TibialisAnterior
DISCUSSION
CONCLUSIONS
FUNDING
ACKNOWLEDGEMENTS
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTIONS
ORCID
REFERENCES

• Ki-hyeon Park(Deptment of Physiotherapy Center, DongHo Orthopedic Clinic, Daegu)
• Dong-hyun Kim(Institute of Human Ecology, Yeungnam University, Gyeongsan, Korea) Corresponding author