Electromyographic and Kinematic Analysis of Lower Limb Function During Standardized Bodyweight Squats in Individuals with Flexible Flatfoot

Background: This study explores the effects of flexible flatfoot on movement stability and muscle activation patterns during bodyweight squats. Since flatfoot alters biomechanics and squats are important in strength and prevention of injuries, their interaction is studied to improve rehabilitation and training interventions.
Methods:24 university amateur male athletes (12 with FFF, 12 healthy; age 18–28 years, ≥3 weekly strength training sessions) performed bodyweight squats to 90° knee flexion. Electromyography of Tibialis Anterior, Gastrocnemius, Vastus Medialis Oblique, Gluteus Maximus, and Quadratus Lumborum, along with kinematic analysis of ankle, knee, hip, and pelvis, were measured within the 0–90° knee flexion range. Comparisons between groups were made for eccentric and concentric phases.
Findings: Compared with controls,the FFF group showed significantly reduced activation of the VMO (eccentric: P= 0.023; concentric: P= 0.026) and TA (eccentric: P= 0.001). Conversely, Gmax activity was higher in both phases (eccentric: P= 0.001; concentric: P= 0.041). Kinematic analysis also showed reduced flexion angles at the hip, knee, and ankle joints during the eccentric phase (P= 0.025, P= 0.055, P= 0.025, respectively). Pelvic abduction–adduction range of motion increased significantly in the concentric phase (P= 0.037), while non-significant decreases were observed in hip, knee, and ankle extension ROM (P= 0.055).
Conclusion: This study demonstrated that the flexible flatfoot condition alters muscle activation patterns, reducing VMO and TA activation and elevating Gmax activation, and limits lower limb joint mobility when squatting, potentially impairing the quality of movement. These findings warrant the application of individualized rehabilitation approaches and promote investigations in diverse populations.