Electromyographic Study of the Extrinsic and Intrinsic Foot Muscles in Flexible Flat Foot during Functional Weight-bearing Positions: Cross-sectional study

Introduction: Flatfoot is a condition characterized by reduced height of the medial longitudinal arch especially during weight-bearing, which influences foot muscle activities.Purpose: To compare the electromyographic activity (EMG) of the extrinsic and intrinsic foot muscles (EFMs and IFMs) of flexible flatfoot versus healthy volunteers in different weight-bearing positions. Also, to determine whether there was a correlation between the activity of these muscles across static phases of six weight-bearing positions. Methods: Thirty-four Subjects with a mean age (y) of 30 ± 10 were recruited according to the height of the medial longitudinal arch as measured by the navicular drop test. They were assigned into two groups; Group A: normal arch and Group B: flatfoot (>10mm drop). The muscle activity of the Tibialis posterior (TP), Peroneus Longus (PL), Abductor Hallucis (AH), and Flexor Digitorum Brevis (FDB), was measured in six weight-bearing positions; bilateral limb stance, single limb stance, bilateral squat, single squat, bilateral heel raise, and single heel raise.Results: No statistically significant differences were found in EMG activities of the TP, PL and AH between the groups across various positions. The FDB muscle activation during the Bilateral Heel Raise, however, showed a significant difference, according to the Wilcoxon test (p = 0.048). Significant inter-muscle activity correlations in all assessed postures were observed.Conclusion: subjects with flatfeet and age-matched volunteers show no difference in EMG activities of leg and foot muscles in different weight-bearing positions. Nonetheless, variations in the FDB muscle activation indicate varying muscle coordination patterns between groups.