1. Introduction
he foot has a special structure; while providing a reliable level of support for standing, walking and moving, it bears a lot of pressure [1]. In order to stabilize and move the lower limb, the end of lower limb structures including the joints, ligaments, and muscles of the ankle and foot, are designed in such a way that can be able to bear the body weight with the least amount of energy while standing [2]. Foot deformity is one of the most common causes of pain, fatigue and dysfunction [4]. Flat foot is one of the most common foot deformities in the foot, which refers to loss of the medial longitudinal arch of the foot, and varies depending on the severity and amount of medial longitudinal arch loss.
One area that has recently attracted the attention of many researchers in the field of medicine and sports is the analysis of the distribution of plantar pressure. Measuring the plantar pressure distribution is one of the common methods that, while identifying the structural deformities of the foot, examines the performance of the foot in static and dynamic conditions, including walking [6]. Improper distribution of forces can cause abnormal movements and excessive stress and damage the tissues and muscles of the foot [8]. Center of pressure and peak pressure in different plantar areas are major factors in gait studies [9]. Foot plantar pressure analysis has opened up a new perspective on lower limb pathology. Many researchers have used the peak pressure on the foot sole in the stance phase of gait to find the causes of lower limb pain and injury [10]. In people with flat feet, due to the disturbance of the normal body alignment caused by the loss of arch, the amount and direction of the forces applied to the foot may change in different gait phases. Due to the fact that the foot is one of the most important parts of the body while walking, it has three functions: force absorption, ground contact, and transfer of propulsive forces [11]. Measuring the amount of force while walking has recently become a criterion for identifying or classifying people based on the pattern of their use of forces during walking [12]. Other kinetic parameter that is used to identify risk factors is the area under the reaction force curve (Impulse) [13]. Due to scant research on the comparison of plantar pressure variables such as force, pressure and impulse among men and women with flat feet, this study aims to compare the parameters of foot plantar pressure (ground reaction force, plantar pressure and impulse) in young people with flat feet while walking.
2. Methods
The study population consisted of non-athlete students with flat feet and normal feet. Of these, 48 were selected using a convenience sampling method. The peak plantar pressure, peak plantar force and impulse applied to the sole during walking were measured by a foot scanner at a sampling frequency of 253 Hz. Shapiro-Wilks test was used to examine the normality of data distribution, and data analysis was performed using MANOVA in SPSS software, considering the significance level at P<0.05.
3. Results
Men with flat feet had more peak plantar pressure and force in the midfoot than healthy men, and more peak plantar pressure on the hallux. Women with flat feet had more peak plantar pressure and force on the hallux, toes T2-T3-T4-T5, M2 metatarsal head, and midfoot than healthy women. Men with flat feet had peak plantar pressure on the M4 metatarsal head than women with flat feet (Table 1). 


Men with flat feet had different plantar impulses in the hallux, M2 metatarsal head, and lateral heal. Women with flat feet had more plantar impulses in the hallux, toes T2-T3-T4-T5, and midfoot than healthy women. There was a significant difference between men and women with flat feet in plantar impulses in metatarsal heads M3 and M4, midfoot, and lateral and medial heels
4. Discussion and Conclusion
Different effects of gender and sole structure on the distribution of plantar pressure should be considered in the production and design of shoes, medical insoles and special sports footwear.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of Hamadan University of Medical Scieneces (Code: IR.UMSHA.REC.1398.256). All ethical principles are considered in this article. The participants were informed about the purpose of the research and its implementation stages. They were also assured about the confidentiality of their information. They were free to leave the study whenever they wished, and if desired, the research results would be available to them. 

Funding
The paper was extracted from the MA. dissertation of the first author at the Department of Physical Education, Faculty of Humanities, Hamedan Branch, Islamic Azad University, Hamedan.

Authors' contributions
Conceptualization: Ali Jalalvand; Research: Ali Jalalvand, Negin Soltani; Editing and finalizing: All authors.

Conflicts of interest
The authors declared no conflict of interest.


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