Evaluation of the balance system in amateur kickboxers

Abstract

Background

Kickboxing is defined as an eclectic combat sport created by combining close combat practices. While the effect of kickboxing on balance function may seem evident, controlled studies that investigate the impact of kickboxing on static and dynamic balance using objective tests are limited.

Objective

The primary aim of this study was to evaluate the effects of kickboxing on the development of static and dynamic balance in amateur kickboxers using objective tests. Specifically, we sought to assess how kickboxing training influences postural abilities and balance systems.

Methods

A total of 20 amateur kickboxers between ages 18 and 26 years (mean age, 21.6 ± 5.65 years) and 20 healthy subjects between ages 19 and 25 years (mean age, 21.3 ± 1.41 years) who had no previous experience with kickbox sports training were recruited. The sensory organization test (SOT), adaptation test (ADT), limit of stability (LOS), rhythmic weight shift (RWS) test, weight bearing/squat (WBS) test, and unilateral stance (US) test of the computerized dynamic posturography (CDP) were used to evaluate both groups. All these subtest results were compared between amateur kickboxers and the control group. All subtest results were compared between amateur kickboxers and the control group using independent sample t-tests. An alpha level of 0.05 was set for statistical significance.

Results

A statistically significant difference was found in the weight bearing/squat (WBS) and limit of stability (LOS) subtest results of the CDP between amateur kickboxers and the control group compared to the control group in amateur kickboxers (p < 0.05).

Conclusions

An increase in LOS and WBS skills was observed in the amateur kickboxers who participated in this study when compared to similar-aged individuals who did not participate in kickboxing. These balance differences may be greater in more elite-level kickboxers who have trained for longer. In addition, other balance parameters may also improve with longer periods of exposure and increasing skill complexity performed at more elite levels.

Background

Kickboxing is known as a combat sport that involves two athletes hitting each other at full strength with their hands, elbows, and feet [1]. Dynamic balance must be ensured in kickboxing, and the muscle strength of both the upper and lower extremities is one of the most crucial elements of success in this sport [2, 3]. One of the parameters that will provide physiological and motor movement properties in sports is balance performance [4]. To be more specific, balance is the ability to keep the body mass in the balance area on a support surface [5, 6]. On the other hand, static postural control can be defined as the ability to maintain the center of gravity with minimum movement, while dynamic postural control can be defined as the ability to perform a task while maintaining a stable position [7]. Balance is crucial for achieving high performance and displaying skill in a variety of sports. Balance can be divided into static balance and dynamic balance. Static balance is the ability to maintain postural stability in a certain position, whereas dynamic balance is the ability to maintain stability while the body is in motion [8]. Both static and dynamic balance require the elicitation of appropriate muscle contraction patterns to maintain postural stability using feedback from the vestibular, visual, and somatosensory systems [9].

Dynamic balance plays a crucial role for sportive movements to occur successfully, maintaining the position of the body and also changing the direction of the body. Dynamic balance also relies on sensorimotor information that minimizes displacements of the center of the gravity while maintaining an upright position, proper orientation, adapted movement, and adequate gestures, figures, or techniques imparted to the practiced sport. Balance plays an important role in sports performance [5, 9]. In addition, sensory information that comes from the somatosensory, visual, and vestibular systems affects the range of motion and strength of motor reactions for dynamic balance [7]. It has been observed that sportive exercises increase the ability to use somatosensory information, and it has been suggested in many studies that combat sports can positively affect postural stability, physical fitness, and health [10, 11].

With regard to a study conducted among young people and adults, it has been observed that taekwondo, karate, judo, and kickboxing significantly improve physical and motor skills [12]. There are few studies in the literature that objectively evaluate the balance system of athletes. This study we conducted with the subtests of computerized dynamic posturography (CDP) such as sensory organization test (SOT), adaptation test (ADT), limit of stability (LOS), rhythmic weight shift (RWS) test, weight bearing/squat (WBS) test, and unilateral stance (US) will support the literature in a clinical sense. The primary aim of this study was to evaluate the effects of the sportive exercises performed by kickboxers on the development of their postural abilities and balance systems. In addition, a secondary aim of this study was to investigate differences in the dynamic and static balance of those undertaking kickboxing when compared to individuals who do not do any sports.

Methods

Participants

The study included volunteer athletes from four different sports clubs affiliated with the Turkish Kickboxing Federation. The experimental group consisted of 20 amateur kickboxers aged 18–26. The control group comprised 20 individuals aged 19–25 who did not engage in any sports or physical activities that support the balance system, such as dancing, yoga, tai-chi, or similar activities. The average age, body weight, and height of the participants are provided in Table 1.

Table 1 Comparison of demographic characteristics, hearing sensitivity, and sensory organization test scores between control and kickboxer groups

All participants provided written consent. The inclusion criteria for the experimental group were participants: (a) whose body mass index (BMI) was in the normal range; (b) without any chronic disease; (c) whose pure tone average (500 Hz, 1000 Hz, 2000 Hz, 4000 Hz) was below 20 dB HL; (d) no air-conduction pure-tone hearing threshold exceeding 40 dB HL at any frequency; (e) normal findings in acoustic immittance evaluation, (f) at least one year of kickboxing training, and (g) no lower extremity injuries in the last 6 months.

The inclusion criteria for the control group were similar, except they did not participate in kickboxing or any other physical activities that support postural stability.

The exclusion criteria for both groups were participants: (a) with any diagnosed peripheral or central vestibular pathology, (b) with any diagnosed orthopedic/neurological pathology. Additionally, the control group excluded individuals who played sports or engaged in any physical activities that support postural stability, such as yoga, tai-chi, or dance training.

All participants were right-handed and had a dominant right leg.

Procedure

Audiological evaluation

Pure-tone and speech audiometry tests were performed using the Aurical clinical audiometry device (GN Otometrics; Taastrup, Denmark). Pure-tone averages were determined by averaging hearing thresholds at 500, 1000, 2000, and 4000 Hz. Acoustic immittance evaluation was performed using the GSI TympStar Middle Ear Analyzer Version 2 (Grason-Stadler Inc., Tiger, USA). The participants’ static and dynamic balance skills were evaluated using the smart equitest computerized dynamic posturography (NeuroCom Balance Manager Systems) system. Various subtests of the computerized dynamic posturography (CDP) system were administered.

Computerized dynamic posturography (CDP) subtests

Sensory organization test (SOT): This test measures the ability to maintain an upright posture under changing sensory conditions. Three trials were conducted for each sensory state, with participants instructed to maintain an upright stance. Performance metrics included postural stability, center of gravity (COG) sway, composite balance score, somatosensory (SOM) value, vestibular (VEST) value, visual (VIS) value, visual preference (PREF) value, composite score, and strategy analysis scores. Equilibrium scores were calculated by dividing the participant's maximum anterior/posterior sway by the theoretical maximum total sway (12.5°) and multiplying by 100.

Adaptation test (ADT): This test involves two series of sudden platform changes causing ankle flexion, each series comprising five trials. Reaction scores in toes-up and toes-down situations were analyzed. The adaptation score reflects the shear force used to correct posture, with lower scores indicating better adaptation.

Limits of stability (LOS) test: This test examines dynamic postural stability. Participants stood on a platform and reached eight different targets displayed on a screen without moving their feet. The dependent variables measured included reaction time (RT), motion velocity (MVL), endpoint excursion (EPE), maximum excursion (MXE), and directional control (DCL). Higher RT scores indicate lower performance, while higher MVL, EPE, MXE, and DCL scores indicate better performance.

Rhythmic weight shift (RWS) test: This test evaluates the ability to transfer the center of gravity along the anterior–posterior and mediolateral axes at three different speeds (3-, 2-, and 1-s sway periods). Movement velocity and directional control were measured.

Weight bearing/squat (WBS) test: This test measures the percentage of body weight borne by each leg at four different flexion positions (0°, 30°, 60°, and 90°). During the WBS assessment, participants were instructed to maintain equal weight on both legs. Deviations from 50% indicate degraded weight-bearing ability.

Unilateral stance (US) test: This test assesses balance during a unilateral stance (standing on 1 leg). Three recordings of 10 s each were obtained in four conditions (right foot eyes open, right foot eyes closed, left foot eyes open, and left foot eyes closed). Sway velocity was calculated by dividing the change in the center of gravity by the trial time, with higher speeds indicating instability.

Ethical considerations

The study was conducted in the Department of Audiology and Speech Disorders and the Department of Otorhinolaryngology at Cerrahpaşa Faculty of Medicine, Istanbul University. The experimental study was approved by the Cerrahpaşa Medical Faculty Clinical Research Ethics Committee. All participants provided written informed consent.

Statistical analysis

Statistical analyses were performed using IBM® SPSS® Statistics version 24 (IBM, Armonk, New York, USA). To verify the normality of the data, the Shapiro–Wilk test was used. All continuous variables were normally distributed. Descriptive statistics, including mean, standard deviation, and percentage, were used to visually examine the data. Independent Sample t-tests were employed to compare the means of independent samples, with significance set at p < 0.05.

Results

The results of this study investigated the static and dynamic balance differences between kickboxers and age-matched non-athlete controls. Key findings included statistically significant differences in several dynamic balance parameters measured by the CDP system. Descriptive statistics regarding the age, height, weight, and audiometric findings of the sample are shown in Table 1.

Sensory organization test (SOT)

Somatosensory, visual, vestibular, preference scores, strategy analysis, and composite scores were compared between the two groups. The results showed that there were no statistically significant differences between the groups for all values (p > 0.05). Detailed descriptives and results of the statistical analysis are provided in Table 1, and the SOT results are visualized in Fig. 1.

Fig. 1

Sensory organization test, adaptation test, and unilateral stance comparisons between control and kickboxer groups. The adaptation test scores are shown for five trials each in the toes up and toes down tests. The sensory organization test (SOT) equilibrium scores include composite, somatosensory, visual, vestibular, visual preference, and strategy analysis scores. Rhythmic weight shifting is analyzed in terms of on-axis velocity (°/s) for left-to-right (LR) and forward-to-backward (FB) weight shifting. Directional control percentages are also shown for these directions. Lastly, the unilateral stance test presents sway velocity (°/s) for the left and right foot with eyes open (EO) and eyes closed (EC)

Adaptation test (ADT)

In the ADT, adaptation scores of both groups were compared for each trial of the toes-up and toes-down test modalities. There were no significant differences between the groups (p > 0.05). Detailed descriptives and results of the statistical analysis of the ADT adaptation scores for each trial are given in Table 2, and the findings are visualized in Fig. 1.

Table 2 Adaptation scores for toes up and toes down trials in control and kickboxer groups

Limits of stability (LOS) test

In the LOS test, five variables (reaction time (RT), motion speed (MVL), endpoint excursion (EPE), maximum excursion (MXE), and directional control (DCL)) were compared for eight different targets between the two groups. Statistically significant differences were found in the following scores: LOS forward MXE (p = 0.041), LOS forward DCL (p = 0.036), LOS right-forward EPE (p = 0.045), LOS right MXE (p = 0.049), and LOS left MXE (p = 0.010), all in favor of the kickboxers. LOS test results for each group and the statistical analysis are given in Table 3, with the findings visualized in Fig. 2.

Table 3 Comparison of reaction time, movement velocity, and excursion metrics of the limits of stability test between control and kickboxer groups

Fig. 2

Limits of stability and weight-bearing squat comparison between control and kickboxer groups. The reaction time (s) measures the time taken to initiate a movement in different directions: forward (F), right-forward (RF), right (R), right-backward (RB), backward (B), left-backward (LB), left (L), and left-forward (LF). Movement velocity (°/s) indicates the speed of movement in these directions. Endpoint excursion (%) represents the percentage of the endpoint reached during movement, while maximum excursion (%) shows the maximum excursion percentage achieved in each direction. Directional control (%) indicates the percentage control over the direction of movement in these same directions. Additionally, weight-bearing squat metrics are shown as weight-bearing symmetry percentages for various angles: left (L) at 0°, 30°, 60°, 90°, and right (R) at 0°, 30°, 60°, 90°. Deviations from 50% represent altered weight bearing symmetry

Rhythmic weight shift test (RWS)

In the RWS test, the scores of the experimental and control groups were compared by taking the average of the sways of the participants at three different speeds (slow, medium, fast) in the front-back and left–right planes. There were no significant differences between the groups (p > 0.05). RWS test results are given in Table 4 and illustrated in Fig. 2.

Table 4 Rhythmic weight shifting, unilateral stance, and weight symmetry measures in control and kickboxer groups

Weight bearing/squat (WBS) test

In the WBS test, the scores of the athlete and control groups were compared in the upright stance position and three flexion positions. A statistically significant difference was found in favor of the kickboxer group regarding weight-bearing symmetry in the 90° flexion position (p < 0.05). The kickboxer group exhibited almost symmetrical weight bearing on both legs during 90° flexion, while the control group showed distorted weight-bearing symmetry, placing more weight on the right leg (p = 0.026 for the left foot and p = 0.030 for the right foot). All participants in the control group shifted more weight to their dominant leg (right leg for all participants) during the 90° flexion squat. WBS findings are detailed in Table 4 and visualized in Fig. 2.

Unilateral stance (US) test

Sway velocity scores were compared under four different conditions (eyes open/closed and right/left leg) in the US test. The results revealed no significant differences between the two groups (p > 0.05). Since all participants were right-handed with a dominant right leg, no comparisons regarding dominant hand/leg grouping were conducted. Findings are detailed in Table 4 and visualized in Fig. 2.

Discussion

Kickboxing is a combat sport that involves throwing punches and kicks either individually or together. This sport includes postural movements necessary to improve balance [13]. In addition, among these postural movements, rapid rotational movements of the head and upper body are thought to be helpful in training the vestibular system [14]. In light of these modifications, it is anticipated that individuals engaged in kickboxing will exhibit disparities in both dynamic and static balance when compared to those who do not partake in this athletic pursuit. Studies suggest that engagement in the literature and marital arts sports have been found to improve balance [15, 16]. While the effect of kickboxing on balance function may seem evident, controlled studies that investigate the impact of kickboxing on static and dynamic balance using objective tests are limited.

In a study by Fong et al. [17], the balance scores of 21 young adults who received taekwondo training were compared to those of 21 young adults who did not receive any training. The results of this study indicate that taekwondo training may contribute to the development of postural control and vestibular function. In another study [18], the findings of the SOT, motor control test (MCT), and ADT, which comprise the three subtests of the CDP, were compared between female soccer players and the control group. Football players exhibited statistically higher composite balance scores in the SOT test. The authors proposed that football players demonstrate superior postural stability. On the contrary, the findings of our study indicated no statistically significant differences regarding the SOT and ADT scores between the kickboxer and control groups (p > 0.05). The observed results may be attributed to the differing degrees of proprioceptive acuity that can develop in response to participation in different sports, or alternatively, to the relatively variable training duration typically engaged in by amateur kickboxers. Vomáčková [1] selected a total of 16 people between the ages of 22 and 35 in his study to determine the effect of sports activity on postural stability, and the selected individuals were divided into two groups of 8 individuals according to their sports focus (fighting, baseball, etc.). In addition, the postural stability scores of both groups were measured using CDP. The mean scores of the LOS test scores were better in the individuals who participate in martial arts as compared to basketball players, while baseball players achieved a higher balance score on the SOT compared to individuals who do martial arts. We found that kickboxers had better LOS scores compared to the control group (p < 0.05). These results are consistent with studies by Vomáčková [1], who have demonstrated the effects of different sports branches. To be more specific, kickboxers performed better stability limits in the right-left and forward directions (LOS1 (forward), LOS2 (forward-right), LOS3 (right), and LOS7 (left)) compared to the control group. Thus, it is thought that kickboxing improves the ability to control the center of gravity in forward, right, and left directions.

Muscle strength in both the upper and lower extremities is a critical determinant of success in kickboxing. In particular, upper extremity strength is a crucial factor in attaining a high level of performance in this sport. Moreover, head, trunk, and arm (HAT) movements facilitate the body’s oscillation in mediolateral directions [19]. In one study [9], 8-week balance training was given to 18 healthy male participants between the ages of 16–32. A significant improvement was seen in the balance scores of the participants before and after the training in terms of the posteromedial and posterolateral test parameters. The information presented hypothesizes that the enhanced strength of the upper extremity muscles observed in kickboxers enables them to better control their bodies in the right and left directions compared to individuals who do not engage in such activities.

In kickboxing, the hip, abdomen, and waist are of great importance for maintaining balance and strength, both of which are essential for executing technical moves. Moreover, hip rotation is an effective technique for punching and kicking. It is essential that the muscles of the hip be both strong and balanced in the pre-, during, and post-kick phases [3]. The results of our study indicated statistically significant differences in the 90° left and right directions in the WBS test (p < 0.05). The results of this study indicate that kickboxers develop their abdominal and hip muscles in accordance with the direction used. In kickboxing, there are a variety of kicking techniques that utilize one leg, including techniques such as kicking with the fist, changing the direction of the kick, and others. Therefore, single-leg training is essential for enhancing single-leg functionality [20]. The WBS findings also show that kickboxers are able to maintain their balance symmetrically even under challenging conditions. The control group loaded their weight on their right foot (on the dominant foot) in the 90° squat condition, so there was asymmetry regarding weight distribution. This is probably related to kickboxers having better-developed muscle groups for performing squats. However, we could not identify any differences related to handedness or leg dominance, as all participants in our study were right-handed and right-footed.

In a recent study [21], it was observed that elite judo athletes with at least 10 years of training experience at the national level had unilateral ankle and knee fatigue. In contrast, our results from the US test did not reveal any statistically significant difference between the kickboxers and the control group. Thus, we can assume that this might be because the kickboxers were not selected from the elite level. In this regard, if the kickboxers were chosen from the elite level, there could be significant differences in US test scores between the kickboxers and the control group depending on the unilateral leg exercises performed during the training.

Moreover, changes in the static and dynamic movement patterns utilized for the coordination and balance of the body are of significant importance in maintaining postural equilibrium while performing the movements inherent to kickboxing. Korobeynikov et al. [22] demonstrated that the sway area of the total center of mass of the body decreased in kickboxers with a high level of postural stability. Moreover, kickboxers with a high level of postural balance have been found to exhibit lower values of static muscle strength and visual-motor response speed. Slimani et. al. [1] observed that elite male kickboxers utilize upper-extremity techniques more frequently than lower-extremity techniques. The findings of our study indicated that, contrary to our initial expectations, the performance differences between kickboxers and the control group were not as pronounced as anticipated. Statistically significant differences were observed in only two of the tests conducted (WBS and LOS). It is postulated that these findings may have been influenced by the fact that the kickboxers were selected from the amateur level, and the duration of their participation in the sport varied. Additionally, the descriptive values show that kickboxers, although not statistically significant, had better mean values in all tests. This could be attributed to the low sample size and the varying levels of experience in kickboxing. More studies with larger sample sizes are needed to elucidate the effect of kickboxing on static and dynamic balance. Nevertheless, the results of this study indicate that even brief engagement in kickboxing may result in positive changes in balance parameters.

Conclusions

The results of this study, which involved amateur kickboxers, demonstrate that the mean scores in the CDP subtests were higher in kickboxers compared to controls. Notably, kickboxers demonstrated statistically significant superior performance in the LOS and WBS tests. These findings suggest that the balance systems of amateur kickboxers show greater improvement over time compared to controls who do not engage in activities that enhance balance performance. It can also be inferred that the initial development of balance parameters in kickboxers is directed toward enhancing weight transfer ability and reaching limits of balance stability. Additionally, it is notable that this study is among the few that have evaluated the balance system of amateur kickboxers. Future research should consider including a larger sample size to improve the generalizability of the findings. An alternative approach would be to compare the balance systems of elite kickboxers with those of non-elite kickboxers.