Comparative Impact of Core Stabilization vs Proprioceptive Neuromuscular Facilitation Exercises on Muscle Activation, Endurance, and Balance in Obese Children: A Randomized Controlled Trial

Introduction

Childhood obesity has become a global public health problem. Obesity is characterized by excessive fat accumulation in adipose tissue [1]. The most commonly used method to measure and detect obesity is body mass index (BMI) [2]. World Health Organization (WHO) published BMI z score values and percentile curves for ages 5 to 19 in 2007. BMI >+1 standard deviation (SD) defines overweight and BMI >+2 SD defines obesity in children ages 5 to 19 years [3]. Obesity negatively affects many body systems, increasing the risk of various health problems such as musculoskeletal disorders, cardiovascular and metabolic disorders, and gastrointestinal and respiratory diseases [2].

Abdominal obesity, in particular, causes an imbalance in the muscles around the pelvis and this imbalanced muscle pattern can lead to abdominal muscle weakness [4]. As BMI increases in children, the strength of the core area decreases [5] and static and dynamic balance disorders are observed [6]. All these factors can cause impaired JPS [7].

The core area, known as the motor control center, has a three-dimensional cylindrical structure consisting of muscles in the body and wrapping the body like a corset [8]. Its most crucial function is to maintain body stability and to provide force and velocity flow to the extremities by providing stabilization in the body before extremity movements [8]. Hence, it is very important that the core area has sufficient strength and endurance [9].

CSE focuses on the core musculature, which includes the transverse abdominis (TrA) and rectus abdominis, internal and external obliques, and paraspinals, as well as the gluteals, pelvic floor, and hip muscles [10]. CSE are one of the exercises used to protect and improve body stability. The objective of these exercises is to increase the strength and endurance of the core muscles, improve lumbar JPS [11], and reduce muscle imbalances by improving dynamic balance and muscle coordination between the lower and upper extremities [12].

The PNF technique is a treatment method that is used to stimulate proprioceptors and facilitate normal responses [13]. It has been reported that PNF techniques can help patients improve muscle strength, muscle endurance, joint mobility, joint stability, neuromuscular control, balance, and coordination [13]. As the diagonal and spiral patterns of PNF are similar to the topographic arrangement of muscles used in daily activities and sports, it is believed that PNF training facilitates the function of several muscles better than unidirectional exercises [14]. PNF exercises have been recommended to improve lumbar JPS by stimulating the proprioceptors of the lumbar region, as well as sensorimotor control training [15]. Thus, improving proprioception via PNF training may benefit lumbar stability [14,15].

In the literature, studies on obese individuals have shown the positive effects of core stabilization exercises and trunk stabilization exercise programs with PNF on core muscle activation, lumbar core muscle endurance, lumbar JPS, and balance [16–18]. However, only 1 study has compared core stabilization and PNF exercises in overweight women [16]. Although obese women were not included in this study, it was determined that core stabilization exercises were more effective than PNF exercises consisting of rhythmic stabilization and combined isotonic contractions in improving balance and endurance [16].

To the best of our knowledge, no study has been conducted to date examining the effects of core stabilization and PNF exercises on core muscle activation, lumbar region muscle endurance, lumbar joint position sense, and balance in obese children. Therefore, this study aimed to evaluate the effects of CSE and PNF exercises on core muscle activation, core muscle endurance, proprioception, and balance in 80 obese children.

Material and Methods

ETHICS APPROVAL AND STUDY DESIGN:

The study protocol was approved by the Eastern Mediterranean University Health Ethics Subcommittee (permission dated 01.07.2020 and numbered 2020/06) and registered on Clinicaltrials.gov (Registration number: NCT05571085). A total of 80 participants who volunteered to participate in the study and fulfilled the inclusion criteria were informed about the study and the informed consent form was signed by their parents. Our single-blind randomized controlled study was conducted between October 2021 and July 2023 in Kyrenia, Turkish Republic of Northern Cyprus.

PARTICIPANTS:

A total of 451 children aged 10–13 years who received education and training at Şehit Hasan Cafer Primary School and Osman Nejat Konuk Secondary School in Kyrenia District were examined for obesity. During the examination, BMI value was calculated by taking height, body weight, and date of birth. BMI values vary depending on age and sex. The WHO published BMI z score values and percentile curves for ages 5–19 in 2007. According to these values, BMI above +1 SD or between the 85th percentile and 95th percentile is defined as “overweight”, and above +2 SD or above the 95th percentile is defined as “obesity”. After the BMI values were obtained, the presence of obesity (95% percentile and above) was determined over the percentile curves in accordance with the age and sex of the participants [3,19]. As a result of this calculation, 128 children with BMI values above 95% percentile were identified.

Inclusion criteria were BMI above the 95^th percentile for age and sex, had not been on an ongoing diet program for the last 3 months, and had not participated in an exercise or sports program for the last 6 months.

Exclusion criteria were chronic disease requiring continuous use of medication, chronic pain preventing exercise, disease of neuromuscular origin, spinal anomaly, history of spinal surgery, spinal and sacroiliac joint dysfunction, history of injury or trauma, and children who were unable to adequately participate in the study.

DETERMINATION OF SAMPLE SIZE:

Sample size was calculated with G*Power version 3.1.9.2. In the power analysis, the initial sample size was calculated as a total of 66 participants (α=0.05, β=0.20, and Cohen f=0.40). Considering that there might be dropouts from the study, this initial sample size was increased by 20% and the final sample size was determined as a total of 80 participants.

RANDOMIZATION: Using a minimization application running under the DOS operating system, the 80 volunteers who met these criteria were randomly separated into 3 groups. Randomization was done by an independent statistician. Age, sex, socio-economic level, and physical activity levels were all considered while minimizing. Physical activity levels of children were assessed using the Turkish version of the Physical Activity Questionnaire for Older Children (PAQ-C): “1” indicates low level of physical activity, and “5” signify high level of physical activity [20]. The Family Affluence Scale [21] was used to assess socio-economic status. The scale has a score ranging from 0 to 9 points: 0–2 points indicate low socio-economic level, 3–5 points indicate medium socio-economic level, and 6–9 points indicate high socio-economic level.

The first group received CSE exercises, whereas the second received PNF exercises. The third group served as the control group, and no intervention was carried out. Participants in the intervention groups were blinded to the groups. The evaluations were done BT, AT, and at follow-up (3 months after treatment). The same physiotherapist conducted all assessments and interventions.

EXERCISE PROGRAMS:

A physiotherapist with 8 years of experience in pediatric rehabilitation carried out CSE or PNF exercise programs. Exercise programs were performed in 3 sessions per week for 8 weeks. Each session lasted approximately 40 minutes (5-minute warm-up, 30-minute main exercise, and 5-minute cool-down period).

The activities were carried out in small groups of 5–8 children. The abdominal hollowing technique was taught to participants during the first 2 weeks of exercises. To guarantee that the participants learned correctly, a pressure biofeedback device (Stabilizer; Chattanooga Group, Inc., Hixson, TN, USA) was employed. The device was inflated to a pressure of 40 mmHg before the contraction began, and the participants were instructed to practice mainly diaphragmatic breathing as previously taught. Because contraction of TrA muscle causes a pressure increase ranging from 4 to 10 mmHg, participants were instructed to maintain this range. Participants were asked to maintain the abdominal hallowing technique throughout the exercises and were regularly reminded.

CORE STABILIZATION EXERCISES: The exercises were based on the program suggested by Jeffreys [22]. The exercises focused on strengthening the abdominal, lumbar, and pelvic muscles and were of increasing difficulty. Jeffreys’ exercise protocol includes 3 levels, starting with level 1 and gradually progressing to level 3. Level 1 consists of static contraction training in a stable condition, level 2 consists of dynamic training in a stable condition, and level 3 consists of dynamic and resistance training in an unstable condition. Pilates balls were used to create the unstable condition [11] (Table 1).

PNF EXERCISE PROGRAM: Dynamic neuromuscular exercises consisting of PNF patterns were progressed in intensity by using gravity, body weight, elastic bands, and exercise balls. During the exercises, no PNF techniques were used (Table 1).

SOCIODEMOGRAPHIC CHARACTERISTICS: Age, sex, height, body weight, and BMI values of the participants were recorded. The Family Affluence Scale [21] was used to assess the socio-economic status of the family.

SAHRMANN CORE STABILITY TEST (SCST): Core stability was assessed by SCST. The SCST comprises 5 tasks of increasing difficulty. The inflatable pad of a pressure biofeedback unit (Stabilizer; Chattanooga Group, Inc., Hixson, TN, USA) was placed in the natural lordotic curve (centered on L4–L5) when the participant was in the supine position. After the pad had been inflated to 40 mmHg, the participant began the SCST. Children were asked to perform abdominal hallowing via pressure biofeedback. Participants performed 3 trials for each level with a 1-minute rest between trials. The level at which participants maintained constant pressure for 10 seconds was noted by the researcher [23].

LUMBAR CORE ENDURANCE TESTS: The core endurance of the participants was evaluated with McGill core endurance tests. This test uses 4-way analysis of the flexor, extensor, dominant, and non-dominant side lateral bridge. The test procedure was explained and taught to the participants. For each test, the time for maintaining the position was recorded [24].

JOINT REPOSITIONING SENSE (JRS): JRS was used to assess lumbar joint repositioning error. All participants sat with feet supported, and hips and knees flexed at 90 degrees. A 10-cm tape measure was placed on the lower lumbar area with the 0-cm end placed on the sacral segment 1 (S1), as the start point of measure and marked by a stable, tripod-mounted laser pointer. Each participant was asked to remember the starting position (neutral position) and maintain it for 5 seconds, then to move their pelvis from the maximum anterior to the maximum posterior tilt, maintain each position for 5 seconds, and return to the starting position. With the laser point on the tape measure, the distance from the starting point (repositioning error) was measured in centimeters. Participants were allowed to practice twice before the examination started. The test was repeated 3 times and results were averaged for analysis [25].

SINGLE-LEG STANDING BALANCE TEST (SLSBT): Static balance of the participants was assessed by SLSBT. Participants were asked to stand on their dominant leg while crossing their arms in front of the chest. The test was conducted for a total of 120 seconds. The stopwatch was stopped when the opposite foot touched the ground or the hands left the chest. The test was repeated 3 times and averaged. The test was done with eyes open and closed [26].

Y BALANCE TEST (YBT): Dynamic balance was evaluated by YBT [27]. The participants were asked to stand on 1 foot at the center point of the test apparatus and touch the toe tip with the other foot while keeping balance in the anterior, posteromedial, and posterolateral directions. The same procedure was repeated for the other foot. The test was repeated 3 times in each direction and results were averaged. The mixed reaching distance of the participants was measured and recorded.

STATISTICAL ANALYSIS:

IBM SPSS Statistics for Windows, version 26.0 (IBM Corp, Armonk, NY, USA) was used for the statistical analysis. Mean (x) and SD for continuous variables, frequency (n) and percentage (%) for categorical variables were reported. One-way analysis of variance was performed for normally distributed variables and the Kruskal-Wallis test was used for non-normally distributed variables in the change of continuous variables according to groups. Post hoc Bonferroni correction was used to determine the different groups for the data conforming to normal distribution, and the post hoc Dunn’s test was used for the data not conforming to normal distribution. The difference between groups with categorical variables was determined using the chi-square test. Repeated measures analysis of variance or Friedman’s test was applied for intra-group variation according to whether the data conformed to normal distribution or not. When there was a difference between the groups before treatment, analysis of covariance (ANCOVA) was performed to control the change before treatment. A value of P=0.05 was used as the probability of error. Clinical effect size was calculated by Cohen’s d effect size analysis. Effect sizes were interpreted as d=0.2 small, d=0.5 medium, and d=0.8 large [28].

Results

GENERAL CHARACTERISTICS:

A total of 80 participants were included in the study. Eight participants dropped out of the groups during treatment. Patients’ reasons for leaving included loss of motivation, going abroad, and the COVID-19 pandemic. Total of 72 patients completed the study (CSE, n=25; PNF, n=23; Control, n=24) (Figure 1). The average age of the participants was 11.57±0.95 years. No adverse effects were reported in any participants. Participants in the groups were statistically similar in terms of sociodemographic features (P>0.05) (Table 2).

CORE MUSCLE ACTIVATION:

When the groups were compared in terms of core muscle activation levels, statistically significant differences were detected between the groups in AT and follow-up (P<0.05). When the groups were compared pairwise, significant differences were detected between the CSE and PNF groups in favor of the CSE group in core muscle activation levels in AT (P<0.05), while the CSE and PNF groups were higher than the control group. Although the core activation levels were statistically similar between the CSE and PNF groups at the end of the 3-month follow-up period (P>0.05), the CSE group maintained its superiority over the control group (P<0.05), (Table 3).

CORE MUSCLE ENDURANCE:

When the flexor, extensor, dominant side lateral bridge, and non-dominant side lateral bridge core endurance values measured with the McGill core endurance test were compared, statistically significant differences were detected between the groups by Bonferroni correction and at follow-up (P<0.05) (Table 4). When the groups were compared pairwise, all core endurance test values after treatment were higher in the CSE and PNF groups than in the control group (Table 4).

Although there was no statistically significant difference between the PNF and CSE groups in the flexor core endurance value at follow-up (P>0.05), the value obtained in the CSE group was statistically significantly different from the control group (P=0.005). The values obtained in the CSE and PNF groups in the extensor, dominant side lateral bridge, and non-dominant side lateral bridge core endurance tests were statistically similar (P>0.05), but the results were significantly higher than in the control group (P<0.05) (Table 4). The clinical effect size was large for flexor core endurance in both CSE and PNF groups (EB>0.8). In other core endurance tests, the clinical effect sizes were small–medium. However, clinical effect sizes were higher in the CSE group than in the PNF and control groups. The effects decreased in the follow-up period (Table 5).

PROPRIOCEPTION:

Lumbar JPS was statistically significantly different between the groups in BT (P<0.05). Therefore, the BT values were controlled by ANCOVA. When the groups were compared in terms of lumbar JPS, statistically significant differences were detected between the groups in AT and follow-up (P<0.05). When the groups were compared pairwise, statistically significant differences were detected between the CSE and PNF, CSE and control, PNF and control groups in favor of the CSE group in AT and follow-up in lumbar joint position sense (P<0.05) (Table 6). When the clinical effect sizes of the treatments for JPS were analyzed, it was found that the clinical effects were large for lumbar JPS in the CSE and PNF groups except for AT and follow-up for PNF group (EB>0.8). However, clinical effect sizes were higher in the CSE group than in the PNF and control groups. The effects decreased in the follow-up period (Table 5).

BALANCE:

When the single-leg balance test was evaluated with eyes open and eyes closed, there was a statistically significant difference between the groups in TS and follow-up (P<0.05). When the groups were compared in pairs, the time taken in the eyes open balance test was statistically significantly higher in the CSE group compared to the control group after treatment and during the follow-up period (P<0.05). In the eyes closed balance test, it was higher in the CSE and PNF groups after treatment than in the control group, while it was statistically significantly different in the PNF group compared to the control group during the follow-up period (P<0.05) (Table 6). There was no significant difference between the groups in dynamic balance tests measured with the YBT (P>0.05) (Table 6).

Discussion

The outcomes of our study demonstrate that CSE is more effective than PNF in increasing the level of core muscle activation, lumbar core muscle endurance, and lumbar JPS, and improving static balance after 8 weeks of treatment. Both treatment programs had equally improved dynamic balance. Clinical effects decreased in the medium term.

CSE was more effective than PNF exercises in increasing core muscle activation level. At the end of the 3-month follow-up period, the superiority of CSE was still maintained compared to the control group. This may be because core exercises focus on the retraining of the TrA muscle [29]. Puntumetakul (2021) compared CSE and body muscle strengthening exercises in patients with chronic low back pain and showed that CSE increased core muscle activation more after 4 weeks of exercise [30]. Our results support previous studies showing that CSE improves core muscle activation.

In parallel with these results, significant improvements were observed in all parameters of lumbar core muscle endurance with CSE and PNF exercises in AT as compared to control subjects. However, the clinical effects of CSE were more significant in AT. Clinical effects decreased at the follow-up period. Boyacı (2018) also indicated that core strength and endurance increased after 10 weeks of CSE in school football players aged 13–15 years [31]. A 2013 study on overweight women found that CSE and PNF exercises improved endurance and balance, and this improvement was more effective than PNF in the CSE group, but the age ranges of the subjects were not stated [16]. Sekendiz et al (2010) found that CSE can increase endurance, flexibility, and balance in sedentary women [32]. Two distinct 4-week PNF programs improved balance, flexibility, and endurance in women with persistent low back pain, according to a study conducted by Kofotolis [33]. These findings suggest that both CSE and PNF training improve core muscle endurance. Although both exercise methods were beneficial in increasing core muscle endurance in our study, the fact that CSE were clinically more effective than PNF exercises may be explained by the fact that PNF exercises were performed using only patterns without using techniques. In addition, methodological differences between the mentioned studies and our study should be kept in mind.

Proprioception in the lumbar region may be reduced due to local body muscle spindle dysfunction, movement error [34], lack of motor function [35], long-term faulty postural adaptations, or postural defects [36]. Lumbar joint repositioning error was considerably reduced in post-exercise assessments in the CSE group, whereas it increased in the control group. This shows that among obese children who do not have CSE, lumbar JPS can worsen over time. The reason why the CSE group improved more than the PNF and control group in terms of lumbar JPS is presumably because CSE stimulates muscle spindles and joint receptors by increasing muscle activity, thereby improving accuracy through sensory-motor integration, and focuses on strengthening the TrA and lumbar multifidus muscles that initiate joint repositioning [37,38]. To the best of our knowledge, there has been no published report evaluating lumbar proprioception in obese individuals after exercise. Puntumetakul (2018) examined the effect of CSE on JPS, pain intensity, and functional disability in patients with non-specific subacute low back pain, showing that CSE can reduce pain and improve proprioception [25]. Hlaing (2021) analyzed the role of CSE and strengthening exercises on proprioception in patients with subacute non-specific low back pain. At the end of the study, CSE was found to be the most appropriate treatment to improve proprioception [29]. Our study confirms that a CSE program can improve lumbar JPS in obese children, but also indicates that PNF exercises can be used, although they are less effective.

In our research, CSE and PNF exercises had similar effects in improving static balance with eyes open and closed. Nevertheless, it was observed that the effect of PNF exercises continued even if the effects decreased in the improvement of static balance measured with eyes closed in the follow-up. Although these findings are parallel to the improvements in lumbar JPS, the improvement in static balance cannot be explained only by the improvement in proprioception. Devarshi and Bamini concluded that in obese children, abdominal bulge and exaggerated lumbar lordosis are due to core muscle weakness leading to deviation from the ideal center of gravity. This leads to deviation of the center of mass (COM) from its ideal location and thus postural imbalance [39]. Babakhani et al found that 8 weeks of CSE improved both static and dynamic balance in girls aged 14–15 years with hyperlordosis [40]. In our study, increases in core muscle activation and endurance and improvements in proprioception may have increased postural control by increasing the stability of the body.

Similar to CSE, PNF exercises have been reported to be effective in development of multifidus, internal obliquus abdominis, and TrA muscles, which play an important role in maintaining balance [41]. In addition, exercises performed with PNF patterns can mobilize joint sensation by moving almost all joints of the body against gravity. PNF improves balance by stimulating proprioceptors located between muscles and joints [42]. A study conducted by Gong in healthy adults determined that dynamic stabilization exercises using PNF patterns helped to increase balance [43]. Similarly, in our study, PNF exercises were performed as dynamic exercises consisting of PNF patterns. Our results suggest that while the stability of the body is maintained through the abdominal hallowing maneuver in PNF exercise training, PNF patterns, in which diagonal and spiral movements are performed involving different body parts, lead to activation of deep abdominal muscles, increase body stability, and indirectly improve balance. Jaspreet et al found that CSE and PNF techniques involving rhythmic stabilization and combined isotonic contractions enhanced balance and endurance in overweight people. The results, however, favored CSE training [16]. Both exercise training programs enhanced dynamic balance and static balance in our study, although they were not superior to one other. The difference between the study of Jaspreet et al and our study could be due to differences in exercise training methodology, as well as the study population.

To the best of our knowledge, this is the first study of PNF exercises, which is original and innovative. Originality is crucial for the advancement of science and the development of new approaches, and we believe that our study contributes to the literature in this context. Additionally, the findings of our study show that PNF-based exercises, conducted without deviating from the core philosophy of PNF, can be effectively used in a targeted manner for obese children. These results highlight the potential of PNF techniques in obese children, making a significant contribution to the literature in this field.

This study had some limitations. First, the fact that our study was conducted only in obese children aged 10–13 years prevents generalization of the results to all children. Second, practically every participant in the PNF group indicated that the exercises were difficult because they used mixed contractions. This could have negatively affected the results by lowering their motivation. Therefore, the use of these exercises in older children in future studies may be beneficial.

Conclusions

Our results suggest that 8 weeks of CSE and PNF exercises improve core muscle activation, lumbar core muscle endurance, lumbar JPS, and balance in obese children. However, CSE was clinically more effective than PNF in all outcome measures. Considering our results and the motivation of the participants and the fact that they performed the exercises more easily from an integrative perspective, it can be argued that CSE is better for use in obese children than PNF exercises. In future studies, PNF exercises should be performed in a double-blind randomized controlled trial using techniques that include various age groups.