The Effect of Locally Produced Unstable Shoes on Foot Plantar Pressure During Walking Among Healthy Male Students

* Corresponding Author: Saed Ahmadi Ganjeh, Msc. Address: Department of Occupational Health Engineering, School of Health, Mazandaran University of Medical Sciences, Sari, Iran. Tel: +98 (917) 1450095 E-mail: saedahmadi1364@gmail.com 1. Department of Occupational Health Engineering, School of Health, Mazandaran University of Medical Sciences, Sari, Iran. 2. Department of Epidemiology & Biostatistics, School of Health, Mazandaran University of Medical Sciences, Sari, Iran. 3. Department of Sports Biomechanics, Faculty of Physical Education and Sports Sciences, University of Mazandaran, Babolsar, Iran. Siavash Etemadi Nejad1 , *Saed Ahmadi Ganjeh1 , Jamshid Yazdani Charati2, Esmail Hoseini Nejad3


Introduction
alking is a perfectly coordinated and complex activity performed in collaboration with the musculoskeletal and nervous systems. The mechanical behavior of these organs has been well identified and analyzed. Such data have been gained by a better understanding of motor organs and relying on sensitive measurement equipment W [1]. Various methods have been used to reduce foot pressure during gait, including wearing shoes, insole, and socks, as well as using surgical procedures and injections [2]. Foot orthoses compensate foot pressure to some extent; however, the biomechanical impact of such tools is unclear [3].
Although prior research has investigated unstable shoe effects, the productivity of such footwear remains unaddressed. Furthermore, unstable shows produced locally are widely available in shoe stores; however, their efficacy and biological impact, compared to those made by foreign countries, have been overlooked. There is no consensus on the biomechanical effects of these shoes on the body. This study examined the effect of locally produced unstable shoes on foot plantar pressure. To this aim, the maximum pressure in ten plantar regions (hallux, lesser digits, 1-5 metatarsals, midfoot, medial, and lateral heels) were considered between different conditions in terms of foot coverage while walking. We aimed to explore the effect of locally produced shoes on foot plantar pressure variables during walking, compared to those produced abroad, conventional shoes, and bare feet condition in healthy people.

Participants and Methods
In total, 20 subjects were selected among healthy rightfooted male students. For evaluating the plantar arch, the navicular drop was measured using the common method [10]. Accordingly, the difference in navicular height between standing and sitting positions were measured and a range of 5-9 mm was considered as normal [10]. To measure the knee varus, the subject stood with lower body naked, knees in full extension, ankles stuck together, and the patella toward the anterior direction. Then, the distance between the two inner epicondylitis of the knee was measured; values <2 cm were considered as natural [9]. To measure the knee valgus, the Tibial Mechanical Anatomical (TMA) angles of 6-9° perpendicular to the axis were considered normal [11]. To avoid immediate effects, before applying walking conditions with different shoes, the study subjects randomly wore the shoes for 20 minutes and began walking on the lab ground.
The walking route was considered about 15 m and the subjects started walking from an 8-m distance from the foot plantar pressure gauge for 3 attempts. The average value of these three attempts was recorded as the subject's rate on walking test under all 4 footwear conditions (locally produced unstable shoes, unstable shoes produced abroad, normal control shoes, and bare feet). The study subjects randomly performed walking test protocols; then, the obtained data were measured and normalized for each subject. A foot scan system (RS-scan, Belgium) with a sampling frequency of 250 Hz and a size of 1×0.4 m was used for measuring variables related to foot plantar pressure.

Results
Variables related to foot plantar pressure, including the surface area of the regions as well as forces applied to it, were combined and analyzed (Table 1).

Discussion
The obtained results suggested that the maximum foot plantar pressure on the regions of 1-4 metatarsals, midfoot, medial, and lateral heels did not depend on the footwear type during gait. Maximum foot plantar pressure on hallux while walking with the foreign-made unstable shoes significantly reduced, compared to the locally-produced ones. There was no significant difference between other investigated conditions.
Maximum foot plantar pressure on lesser digits while walking with the locally-made unstable shoes significantly increased, compared to bare feet condition; however, there was no significant difference between other explored conditions. Maximum foot plantar pressure on metatarsal 5 while walking with the locally-made unstable shoes also significantly increased, compared to walking with bare feet. However, no significant difference was detected between other study conditions. There were significant changes under different footwear conditions in hallux, lesser digits, and metatarsal 5 regions. The pressure difference in these plantar regions could belong to the rigidity and low adsorption properties of unstable shoes. These abnormal pressures could harm the foot sole over time. Our achieved results are consistent with those of Stewart et al. [5] but against those of Kavros et al. [14,15].

Conclusion
Locally-made unstable shoes significantly increased maximum pressure on lesser digits and metatarsal 5 regions, compared to bare feet condition as well as on hallux, compared to foreign-made unstable shoes. This finding indicates that these locally produced unstable shoes not only were unable to decrease the pressure on lesser digits and metatarsal 5 regions but also increased it. This highlights the inefficiency of unstable shoes manufactured in Iran in adjusting the plantar pressure in individuals.

Compliance with ethical guidelines
A written informed consent was obtained from all participants and they were informed of the study objectives and methods.

Funding
This study was extracted from a thesis conducted in collaboration with the Department of Occupational Health and the Department of Ergonomics of the School of Public Health in Sari and the Health Assessment and Monitoring Center of the University of Mazandaran.

Conflicts of interest
The authors declare no conflict of interest.