*2.1. Methods*

The subjects were selected from 28 children with diplegia CP undergoing physical therapy at K Hospital in Gyeonggi-do, Korea. The specific selection criteria of the study subjects were children between the ages of 6 and 13 years diagnosed with diplegic CP, who were able to follow the researcher's instructions and had a GMFCS (gross motor function classification system) level between I and III [23]. Children were excluded if they had unstable seizures, had received treatment for spasticity or any surgical procedure up to 3 months (for botulinum toxin type A injections) to 6 months (for surgery) prior to the start of the study—or if they su ffered from other diseases that interfered with physical activity [24].

Subject's age, height, weight, BMI and GMFCS level were measured prior to each intervention to apply the appropriate amount of weight for each intervention. All subjects picked a black or white stone from a box containing 28 stones. Subjects were randomly divided into an experimental group or a control group, with 14 subjects in each group.

One week before training and one week after training proceeded the evaluation. The intervention group performed FPRE for 30 min per day, three times per week, during a period of 6 weeks. For the control group, a conventional physical therapy program was applied instead of FPRE. However, during the intervention, one subject in the FPRE group had to drop out due to their health condition and two subjects in the control group were excluded because they moved out of town.

This study was conducted with the approval of the research institutional review board of Sahmyook University (2-7001793-AB-N-012018014HR) and it was registered (KCT0005055) as a Clinical Research Information Service (CRIS) in Republic of Korea. The objective and the procedures performed in the

study were explained to the subjects' parents, and all of the subjects' parents provided informed consent for inclusion in the study. Therefore, this study was conducted according to the ethical principles of the Declaration of Helsinki.

### *2.2. Experimental Methods*

### 2.2.1. Functional Progressive Resistance Exercise

The FPRE program was modified based on circuit training that follows the program used by US National strength and conditioning association (NSCA). Strength training must be individualized and should involve a progressive increase in intensity to be successful, thereby stimulating strength gains that are greater than those associated with normal growth and development [25]. The FPRE can be used to bear, overcome or resist force, such as body weight, free weights or machines. The exercise was conducted three times per week for 6 weeks. Each exercise was comprised of 5 min of warmup exercise followed by three di fferent types of exercise. Exercise repetition increased to five times in the first two weeks, 10 times in the subsequent 2 weeks and 15 times in the last two weeks. More specifically, according to subject's participation, body weight and exercise repetition will be increased every two weeks by 5%, 10% and 35% based on their body weight. According to each subject's performance both weight and repetition would be increased; however, in the event that the subjects were unable to follow the increase in exercise repetition or weights used during exercise, the level of di fficulty would remain the same.

In the following protocol, three circuit exercises were included: sit to stand, half-kneeling standing up and side step-up. In the sit to stand exercise, the child sits on a bench with no back rest. In the starting position, the child's back, knee and ankle need to be flexed at a 90◦ angle and their ankles should be in contact with the floor. From the starting position, the subject would be instructed by the physical therapist to stand up slowly from the bench. In the half-kneeling standing exercise, the child is sitting in a half-kneeling position without any external support. From this starting position, the child gradually pushes forward to stand up while the weight is shifted forward on the front leg. In the side step-up exercise, the child climbs up a 15 cm staircase sideways [26]. Between each circuit, 30 s to 1 min of rest time was given to subjects. Longer rest times were given to subjects with lower GMFCS scores to reduce stress. A cooling down exercise and range of motion stretching was held in the final 2 min (Table 1).


**Table 1.** Functional progressive resistance exercise protocol.

FPRE—functional progressive resistive exercise; a Progressively increased to five times, 5% weight in 1–2 weeks; 10 times, 10% weight in 3–4 weeks; 15 times, 35% weight in 5–6 weeks.

### 2.2.2. Conventional Therapy

Conventional therapy, which was prescribed by a rehabilitation doctor in K hospital, included FES, standing frame and mat exercise. In the control group, conventional therapy had a duration of 30 min three times per a week for 6 weeks. The instructor for each exercise was a pediatric physiotherapist with 3 or more years of work experience.

### *2.3. Outcome Measurements*

### 2.3.1. Knee Extensor Strength

In this study, knee extensor strength was measured with a handheld dynamometer FPX 50 (Wagner, Inc., Greenwich, CT, USA, 2017) before and after the intervention by therapists who received 40 min of education regarding proper use of the hand hold dynamometer. The measurement of the knee extensor was performed with the subject in a sitting position, with knee and hip in a 90-degree flexion without back support. Since gravity effects can result in measurement errors, all actions were tested in gravity-neutralized Bryant positions [27]. Subjects were required to place both hands on their lap and HHD was placed 3 cm above the ankle joint. Three attempts were made to find the mean value for the knee extensor strength measurement. The reliability ICC was 0.91 [28].

### 2.3.2. Rehabilitative Ultrasound Imaging

The use of ultrasound imaging (USI) to aid rehabilitation of neuromusculoskeletal disorders or rehabilitative ultrasound imaging (RUSI), is defined as 'a procedure used by physical therapists to evaluate muscle and related soft tissue morphology and function during exercise and physical tasks [29]. In this study, morphology of the quadriceps muscle was measured with portable ultrasound, Medison Mysono *P*-US system (U5, Samsung Medison, Seoul, Korea). The cross-sectional area of the rectus femoris and the thickness of the quadriceps, from the top of the rectus femoris to the bottom of the vastus intermedius, were measured three times on both legs. Regarding the reliability of this test, the interrater reliability ICC was 0.87–0.97, while the intra-rater reliability ICC was 0.78–0.95 in younger people [30].

### 2.3.3. Muscle Tone

In this study, Electronic goniometer, Baseline 12-1027 Absolute+Axis digital goniometer (Baseline, Inc., New York, NY, USA, 2016) was used to measure the popliteal range of motion in passive, speed and active. In supine position ipsilateral hip and knee were flexed to 90◦ and the knee maximally passively extended to the point of mild resistance, active range of motion and range of motion with velocity were also measured in same positions [31]. To provide consistent rate and provide highly reliable measures, it was calculated as the mean of three trials. The ICC for this test was 0.999 [32].

### 2.3.4. Dynamic Balance

In this study, dynamic balance was examined using the functional reach test (FRT). The FRT was performed with a leveled yardstick that was mounted on the wall at the height of the patient's acromion level in the unaffected arm while sitting in a chair. Hips, knees and ankles were positioned at a 90-degree flexion, with feet positioned flat on the floor. The initial reach is measured with the patient sitting against the back of the chair with the upper extremity flexed to 90 degrees; the measurement was made from the distal end of the third metacarpal along the yardstick [33]. The FRT measures the maximum distance that subjects can reach forward (F-FRT) and sideways (S-FRT) with their arm while maintaining a fixed base of support in the sitting position. The distance was measured in centimeters to the second digit. The interrater reliability ICC of this test was 0.99 and intra-rater reliability ICC was 0.97 [34].

### 2.3.5. Functional Ability

Functional ability was scored with the GMFM-88. The gross motor function measure (GMFM) is a five-level classification system that appears to be valid in assessing the child's current motor functions, including laying/rolling, sitting, crawling/kneeling, standing and walking/running/jumping and is

thought to have prognostic potential, i.e., early classification of a child could help determine long-term motor function [35]. The reliability ICC ranged from 0.92 to 0.99 for all dimensions and total scores [36].

### *2.4. Statistical Analysis*

All demographic variables of subjects displayed normal distribution. SPSS version 25.0 statistical software (IBM, Chicago, IL, USA) was used for analysis of all statistical values. Results are presented as mean ± standard deviation. The general characteristics of two groups were analyzed using chi-squared analysis and the independent *t*-test. The interaction effect between group and time was assessed using a repeated-measures analysis of variance. A paired *t*-test was used to compare the results before and after the intervention in each FPRE group and control group. For all tests, the level of statistical significance was set to 0.05.
