Introduction

One of the problems that occur in the lower limb is the abnormal shape of the feet. A flat foot is a medical condition where there is an emphasis on the subtalar joint, which results in internal rotation of the tibia so that the entire foot is directly in contact with the ground [1,1–5]. Research has shown that tendon specimens from individuals suffering from flat feet obtained by adults show signs of increased proteolytic enzyme activity. The constituents of the tendons involved can be broken down by these enzymes and cause the foot arch to collapse. Those enzymes could become targets for new drug therapies in the future. By examining the patient standing or just looking at them, many medical professionals may diagnose a flat foot. The deformity can be corrected when moving up to tip toe when this is a flexible flat foot in a child with loose joints. In adults with a rigid flat foot, the correction is not seen. The wet footprint test, achieved by wetting the feet in water and then standing on a flat level surface such as smooth concrete or thin cardboard or heavy paper, is a simple and conventional home diagnosis. Typically, the flatter the foot, the greater the sole of the foot that makes contact, leaving a footprint. The prevalence of children who have flat feet with an age range of 6 to 10 years in girls is more than the boys. The number of girls who have flat feet reaches 53.4% ​​, while for boys, about 46.6% [6]. The growth of flat feet in children stops when the child reaches ten years of age. Otherwise, it is called a pathological condition. Medial Longitudinal Arch (MLA) grows significantly at age six years, then slows down at ten years old [7,8]. Pathological changes in the formation of the MLA and changes in the shape and length and width of the legs in women occur at the age of 3 to 12 years old, while for men at the age of 15 years [9].

In flat foot conditions, the position of the feet changes towards pronation, with changes in the shape of the feet that will affect the muscles in the knee and leg areas. The intrinsic muscles and extrinsic muscles of the feet work harder and together to maintain posture stability [10]. Posture changes in flat foot conditions can cause problems related to changes in muscle activity, such as stiffness of the lower leg muscles or weakness of the leg muscles [11–13]. The long-term effect of flat foot is a pain in the feet and ankles as well as instability and disorders of the lower back to the lower extremities, which directly or indirectly affect the quality of life [14]. Examination of muscle activity can use a tool, namely surface electromyography (sEMG), which is a tool used to compare muscle activity during contraction [15].

According to research [16–18], the tibialis anterior muscle experienced hyperactivity as measured using surface electromyography (sEMG) in flat foot conditions compared with normal foot conditions. Therefore, we became interested in researching the relationship between flat foot and lower leg muscle activation in children aged 12 years.

Material and methods

Ethical Clearance

This study had received approval from the Health Research Ethics Commission of the Faculty of Medicine, Universitas Muhammadiyah Surakarta.

Research Method

This research was a correlational study with a cross-sectional approach [19,20]. It aimed to determine the relationship between the degree of flat foot and lower leg muscle activation in children aged 12 years old. This research was conducted in the Boarding of Islamic Junior High School Al-Abidin Banyuanyar Surakarta with a population of 40 children and the sample was 15 children with female subjects who met the inclusion criteria.

The criteria for sampling the participants included 1). The subject was a 12-year-old female, 2) she had a flat foot shape, and 3). The participant was willing to take part in a lower leg muscle activation check program. Those with the following characteristics were excluded from the study: 1) A female participant who was not willing to participate in the research, 2) the one who had high Arcus, 3) the one with normal foot, and 3). The participant who had experienced injuries in posture.

Arkus Pedis Examination

Examination of the pedic arch using the wet footprint test method was carried out by placing the soles of the feet moistened with ink or paint on HVS paper. Then, the pedic arch was measured using Clarke's angle category. Calculation of Clarke's angle was done by measuring the angle of two lines, the first line connects the medial edge of the first metatarsal head with the heel (points A and B), and the second line connects the first metatarsal head and the center of the longitudinal arch of the inner medial side of the arch (Points A and C) after measuring the angles [21].

Figure 1: Clarke’s Angle

Clarke's Angle value categories are as follows:

1) Normal Foot: 31^o- <45^o

2) Flat Foot: <31^o

3) High Arcus:> 45^o

Measurement of Lower Limb Muscle Activation

Measurement of lower leg muscle activation was done using surface electromyography (sEMG) under the Noraxon metrics brand using microvolt (µV) units which are represented in the form of numbers. The placement of the sEMG electrode based on SENIAM was as follows:

a) The anterior tibialis muscles: The location of the electrode placement on the tibialis anterior muscle is placed in 1/3 of the line between the tip of the fibula and the tip of the medial malleolus. The maximum size of the electrode used is in the same direction as the muscle fiber, which is 10 mm; the electrode distance is 20 mm, as shown in Figure 2.

Figure 2:EMG placement on the tibialis anterior muscle

b) The medial gastrocnemius muscles: The location for placing the electrodes on the medial gastrocnemius muscle was placed on the most prominent muscle protrusion. The maximum size of the electrode used was in the same direction as the muscle fiber, which is 10 mm, the electrode distance is 20 mm, as shown in Figure 3.

Figure 3:EMG placement on the medial gastrocnemius muscle

c) Gastrocnemius lateral muscle: The location of the electrode placement on the lateral gastrocnemius muscle was placed on 1/3 of the line between the head of the fibula and the heel. The maximum size of the electrode used was in the same direction as the muscle fiber, which is 10 mm; the electrode distance was 20 mm, as shown in Figure 4.

Figure 4:EMG placement on the lateral gastrocnemius muscle

Result and Dissection

Respondents were all females aged 12 years old. The following distribution of respondents was based on the pedis arc.

Table 1:Arcus pedis respondents

Based on Table 1, 40 girls included the sample. There were 45% samples with normal foot conditions, 37.5% with flat foot conditions, and 17.5% with high arcus conditions. This study focused on respondents with flat foot conditions.

The normality test used is the Shapiro Wilk test. Data was shown to be normally distributed if it was known that p> 0.05 and p

Table 2:Normality test results with Shapiro Wilk

Based on table 2, the normality test using the Shapiro Wilk test shows that the flat foot with the lower leg muscles, namely the tibialis anterior muscle, was 0.003, the gastrocnemius medialis muscle was 0.000, and the lateral gastrocnemius muscle was 0.000, so it was concluded that the p-value

Based on the normality test, it was known that the flat foot and lower leg muscle data were not normally distributed, which was stated with a p-value <0.05; the correlation test used in this study was the Spearman rho test.

Table 3:The results of the flat foot correlation test with the lower limb muscle activation