The Effect of Ankle Dorsiflexion on Sagittal Posture and Core Muscle Activation

Maintaining proper posture is essential for preventing musculoskeletal disorders and reducing injury risks. This study investigates the impact of insoles with ankle dorsiflexion (inverted drop sole) on sagittal posture, spinal curvatures, and core muscle activation. Methods: Fifty-five participants (29 men, 26 women; aged 20–70 years) were evaluated in two conditions: barefoot and with insoles incorporating an inverted drop sole. Kinematic data of trunk, hip, and knee angles, along with spinal curvatures (dorsal kyphosis, lumbar lordosis, and sacral slope), were collected using the Simi Aktysis 3D system and the Medi Mouse IDIAG 360®. The electromyographic (EMG) activity of the rectus abdominis and rectus femoris muscles was analyzed using the Bioplux® device. Statistical analyses were conducted using Wilcoxon tests (W) for non-parametric data and Student’s t-tests (T) for parametric data with significance set at p < 0.05. For parametric data, effect size (ES) was used to assess the magnitude of differences based on the Cohen scale. For nonparametric data, the rank biserial correlation (rB) was used, considered an ES equivalent to the correlation coefficient. Results: Significant differences were observed between the barefoot and insole conditions for trunk and knee angles (p = 0.009 and p < 0.001, respectively) with moderate and large magnitude of difference (rB = −0.41 and rB = −0.96, respectively). No significant change in hip angle (p = 0.162) was observed. Spinal curvatures, including dorsal kyphosis, lumbar lordosis, and sacral slope, significantly decreased (p < 0.001), with a large magnitude of difference for dorsal kyphosis, lumbar lordosis, and sacral scope (rB = 0.71, rB = −0.94 and ES = 0.54, respectively). EMG analysis revealed the increased activation of the rectus abdominis and rectus femoris muscles (p < 0.001), with a large magnitude of difference both the rectus abdominis and rectus femoris (rB = −0.82, and ES = −0.82, respectively). Conclusions: Insoles with ankle dorsiflexion significantly improve sagittal posture by reducing spinal curvatures and enhancing core muscle activation. These findings suggest that dorsiflexion technology in footwear may serve as a non-invasive strategy for improving posture, preventing musculoskeletal disorders, and managing low back pain.