aintaining balance is one of the most basic neuromuscular functions in the most of simple and complex activities. Plantar arches play an important role in regulating and distributing plantar pressure. In the healthy people, the presence of longitudinal and transverse plantar arches, support of bone structures and soft tissue stabilizes the subtalar and midtarsal joints. Having stability in these joints during dynamic activities such as walking provides the necessary force to move forward and transfer that force to the foot. Prefabricated insoles increase balance and reduce extra lateral movements by creating more contact surface and more appropriate pressure distribution over the sole of the foot. The presence of musculoskeletal abnormalities such as flat feet and Pes Cavus and structural features of the foot affect the balance of people. Decreased balance leads to decreased performance and provides the basis for injury, especially in the ankle.
Many studies have been done on static and dynamic balance in people with plantar abnormalities, but little research has been done on the effect of medical insoles on the balance of children and adolescents. Since the most daily activities require balance and many injuries occur in static and dynamic positions, the aim of the present study was to evaluate the instantaneous effect of insole on the balance of adolescents with flat foot and Pes Cavus.

This is a descriptive quasi-experimental study conducted on 34 adolescents aged 11-14 years old in Tehran (17 girls and 17 boys; who were randomly selected. A wall mounted stadiometer (model 26 SM) was used to measure the height and a digital scale (BS101) was used to measure the weight in subjects. For assessing their soles, the type of abnormality was determined first by observational method and then by using a foot scanner (3D BodyView, USA). The validity of this device has been calculated by the manufacturer (r=0.64). Its intrapersonal and interpersonal reliabilities using intra-class correlation coefficient were obtained 0.62 and 0.91, respectively. Sharpened Romberg test was used to measure static balance of participants, and ENC device (Danesh Salar Iranian Co., Iran) was used to measure their dynamic balance. 
This device has two parts; a special part for standing and the other part to display information related to the balance. The movement of the person on the screen is in the medial-lateral direction and according to the visual stimulus. This device has biofeedback and the amplitude of postural stability can be adjusted. It can also be used to measure the balance coordination of body organs. It has a measurement accuracy of one degree with a dimension of 105 x 82 cm and the ability to display the percentage of postural balance. The validity of the device has been calculated by the manufacturer using Pearson correlation coefficient between the score of this device and that of Lafayette Manual Muscle Tester (r=0.88). Its intrapersonal and interpersonal reliabilities using intra-class correlation coefficient were obtained 0.93 and 0.91, respectively. 
Kolmogorov-Smirnov test was used to evaluate the normality of data distribution. Descriptive statistics (Mean±SD) were used to describe variables, paired t-test to investigate the instantaneous effect of the insole, and independent t-test to compare the two groups of flat foot and Pes Cavus at a significance level of 0.05.

The mean demographic indicators of the subjects were as follows: the Mean±SD age=12.23±1.18 years, the Mean±SD height= 153.47±10.04 cm, the Mean±SD weight=42.47±6.23 kg, the Mean±SD of stability index=93.29±47.39 degrees, the Mean±SD of right leg length=24.19±0.49 cm, and the Mean±SD of left leg length=24.28±0.46 cm.
The mean of dynamic test score and Sharpened Romberg test score in the post-test phase were higher than those in the pre-test phase. The results of paired t-test showed the significant instantaneous effect of the insole under dynamic balance test (P=0.00), but no significant difference was observed under Sharpened Romberg test (P=0.07). The results of paired t-test for instantaneous effect of insole on the two study groups showed that the use of insoles improved the dynamic balance of subjects with Pes Cavus (P=0.00), but had no significant effect on their static balance (P=0.42). Using the insoles also improved the dynamic balance of subjects with flat foot (P=0.00), but had no significant effect on their static balance (P=0.10) (Table 1).


 
The results of independent t-test to compare the two groups of flat foot and Pes Cavus, showed no significant difference between the two groups in terms of dynamic balance (P=0.99) and static balance (P=0.52) in Pre-test phase. There was no significant difference between the two groups in dynamic balance (P=0.25) and static balance (P=0.72) in Post-test phase, either. These results indicate that adolescent girls and boys with flat foot and Pes Cavus had poorer dynamic balance before using the insoles. Moreover, the instantaneous effect of medical insole on the dynamic balance of adolescents with flat feet was slightly greater than that of those with Pes Cavus, but medical insole had no significant effect on their static balance.

The arches of the sole are very influential on the distribution of force and pressure because the weight of the body is distributed by the talus to the front and back of the foot and then transferred to the ground. Deformity in the foot area for any reason causes numerous problems in people’s daily living activities such as walking, running, standing, and also in the anatomical structure and arches of the soles and affect the balance of people. Medical insoles can systematically reduce pressure over the foot and help posture stabilization by maintaining the arch of the sole and increasing the plantar surface. 
The results of the present study showed that adolescent girls and boys with flat foot and Pes Cavus had poorer dynamic balance before using the insoles. Moreover, the instantaneous effect of medical insole on the dynamic balance of adolescents with flat feet was slightly greater than that of those with Pes Cavus, but medical insole had no significant effect on their static balance. Therefore, it is recommended that people with plantar abnormalities use the mechanical effects of the medical insoles to correct their abnormalities, improve mechanical performance and prevent possible injuries.

All ethical principles are considered in this article.

This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.

All authors contributed in preparing this article.

The authors declared no conflict of interest.

The authors would like to express their appreciation of all of Athletic & Clinical Center, Pouyesh Setaregan Salamt, Tehran, Iran.
 

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