Changes in lower extremity biomechanics and muscle activity after six-minute fast-walk in individuals with flatfoot

Abstract

Flatfoot is a common disorder, which is caused by dysfunction of medial longitudinal arch. Individuals with flatfoot usually exhibit symptoms such as fatigue and discomfort after fast walking, and association syndromes to other lower extremity joints. Therefore, it is important to understand how flatfoot affects the biomechanics and muscle activities of the lower extremity, especially after a challenging walking activity. Fourteen individuals with flatfoot (8M6F, age: 24.5 ± 2.47) participated in this study. All subjects performed maximal voluntary isometric contraction (MVIC) and functional tasks including walking, single-leg standing and sit-to-stand before and immediately after a 6-minute fast-walking protocol. The motion capture (Vicon Motion Systems Ltd, Oxford, UK) system, force plate and the surface electromyography (sEMG) system (MP150, BIOPAC Systems Inc., CA, USA) were used to collect kinematics and muscle activation data respectively. Median frequency and RMS amplitude of EMG, as well as joint angles and moments were calculated and compared using paired t -tests. Most of subjects showed decrease in median frequency (fatigue) in tibialis anterior, but increase in abductor hallucis after 6-minute fast-walking. Also, during stance phase of gait, ankle joint showed more adduction and hip joint showed more flexion at heel contact, decreased knee extension moments at 30% to 50% of stance phase, and decreased hip internal rotation moments at 30% of stance phase. Our study found that tibialis anterior became fatigue after 6-minute fast walking, and as a result abductor hallucis increased muscle recruitment to compensate and provide support to the foot arch. Along with the altered biomechanics of the proximal joints, this challenging fast walking protocol could help explain the mechanism of overuse injury and associated syndromes in individuals with flat foot.