## 2 Materials and Methods
### Measurement of Variables
#### 2.2.5 Foot Strength  
Isometric muscle strength was measured with a handheld dynamometer from the Lafayette Instrument Company, model 01160, Lafayette, IN, USA. This device is factory-calibrated with a sensitivity of 0.1 kg and a measurement range of 0 to 200 kg. Each child sat on an examination table with hips flexed, knees extended, and back supported. Isometric muscle strength for foot inversion and aversion, as well as ankle plantar flexion and dorsiflexion, was measured, taking data from both feet. Strength was measured in Newtons (N). Higher values indicate more strength. The position of the dynamometer for each of the evaluated foot movements was as follows:  
- Inversion: positioned medially over the base of the first metatarsal. -For dynamic gait measurements, the pressure platform was placed in the center of a 10 m long corridor, and the children were instructed to walk barefoot down the corridor ten times. To maintain a constant speed before stepping on the platform, the children had to step on it no earlier than their fourth step. Measurements were obtained by combining all tests for each foot, ensuring 8 to 10 valid footprints per child. Valid footprints were those in which the child had maintained balance while walking (1), was not distracted (such as looking around or talking) during walking (2), and when the entire plantar area was captured (3). The first two criteria were monitored during the scan, and the third criterion was visually evaluated later by the same researcher. To avoid issues with paired data, the plantar pressure results of the left and right feet were averaged into a single observation. The reliability of the Footscan(r) system (RSscan International, Olen, Belgium) has been confirmed in various studies, showing good to excellent ICC for intra- and inter-evaluator assessments (ICC from 0.81 to 0.86 and from 0.87 to 0.95, respectively) in plantar pressure variables [25]. The variables extracted from the baropodometry were as follows:  
Dynamic 2D analysis focuses on foot rocking movements and provides information about the subtalar joint angles and the flexibility of the left and right feet. The following measurements are expressed in \({}^{\circ}\):  
* Fick Angle: The angle of the subtalar joint. It measures the rearfoot movement in the frontal plane relative to the ground during the initial contact phase. A higher value indicates a more pronated rearfoot. * Minimum-Maximum Pronation: Represents the flexibility of the subtalar joint (pronation excursion). The measurements indicate the maximum supination and pronation positions of the rearfoot relative to the ground during the initial contact phase. During Stance Phase of Gait  
Foot time analysis identifies different events and phases during foot movement for both the right and left feet. Each event and phase are expressed in milliseconds and as a percentage of the total movement time. The events and phases for both feet are as follows:  
* Forefoot Contact Phase (ms): duration of foot contact phase. * Foot Flat Phase (ms): the duration between the initial forefoot contact event and the heel-off event. * Forefoot Push Off Phase (ms): the duration between the heel-off event and the last foot contact event. Stabilometric Variables (Static)  
The following parameters were considered: Percentage of pressure distribution between the left and right legs, as well as between the forefoot and the rearfoot. The left forefoot (C1), right forefoot (C2), left rearfoot (C3), and right rearfoot (C4) were also evaluated. Gravity Center Variables  
The following data were also extracted from the center of gravity:  
* Minimum and maximum y-axis and x-axis: the minimum and maximum position, measured in mm for the x and y coordinates. * Distance traveled and right left foot: the length of the center of pressure line, measured in mm. * Ellipse area right and left: the area of the center of pressure ellipse, measured in mm\({}^{2}\).