The Effects of Functional Ankle Taping on Postural Stability in Elite Judo Players

Abstract

The purpose of this study was to investigate the effect of ankle taping intervention on postural stability in elite Judo players. A total of twenty-two elite Judo players participated in this study. For biomechanical evaluation of postural stability, all participants performed postural standing tasks including narrow, normal, and wide stance conditions with both taping and non-taping conditions, respectively. Ground reaction forces and the center of pressure (COP) were obtained from the force plate. COP data for 30-s duration were analyzed to assess postural stability by measuring 95% confidence ellipse sway area (COPSWAY), COP velocity (COPVEL), and approximate entropy (ApEn). Significant differences were found in COPSWAY (p = 0.025) and COPVEL (p = 0.041) in the narrow stance, but no differences in normal and wide stances were observed between taping and non-taping conditions. For ApEn in the anteroposterior (AP) direction, significant differences were identified in normal (p = 0.026) and wide (p = 0.014) stances, but in the mediolateral direction there were no significant differences in all stances between taping and non-taping conditions. This study suggests that ankle taping that is purported to increase ankle stability may ironically negatively affect posture maintenance in Judo players. Our study suggests that the purpose of ankle taping should be reconsidered and associated individual objective data should be first analyzed before tape application.

1. Introduction

Functional taping is a widely used intervention for rehabilitative and injury preventive purposes, and also a popular and common intervention for enhancing motor performance and postural stability in a variety of sporting activities [1]. In particular, the taping intervention has shown several biomechanical advantages [2]. It can increase muscle activation, allowing for an efficient exertion of muscle force. It can also enhance joint kinematics, allowing for an optimal joint range of motion. These taping-related benefits reduce the possibility of injury and reduce pain and inflammation caused by potential injury [1,2]. This in turn may bring positive rehabilitation effects to athletes and reduce time taken for recovery. Furthermore, taping can affect modulations between skin afferent stimuli and motor unit firing, thereby optimizing muscle and fascia function. Such modulatory changes can effectively increase or reduce muscle strength exertion [3]. Thus, the taping intervention changes basic biomechanical mechanisms by facilitating or suppressing the musculoskeletal and nervous systems, improving joint proprioceptive functions and body postural alignment through ligament and tendon support [4,5].

The taping intervention is widely utilized in the sport of Judo. In particular, elite Judo players apply ankle taping in order to facilitate ankle joint movement (i.e., strong joint support leads to better balance) or to reduce the possibility of injury while performing motor skills. Recently, it was reported that among the diverse range of potential physical injuries, top-level Judo players most frequently experienced sprain injuries during competitions [6]. Further, Judo is known for high injury rates during competition or training, with ankle sprain and ankle joint injury being the most common injuries (4.98% and 3.98%, respectively) [7]. Particularly, the ankle joint represents the most important joint in Judo as the play requires standing stably when exerting one’s own force and bearing the counterpart’s exerted force. This means the ankle joint needs to resist forces that are multiple times greater than the weight of the athlete, increasing the risk of an ankle injury [8]. To accommodate for such dynamic and risky characteristics of Judo, most Judo athletes have typically used ankle taping to prevent ankle injury and enhance their performance. Mechanically, taping strengthens the stiffness of the ankle joint to diffuse any overloading on the ankle, thereby reducing the possibility of spraining. This strengthened ankle stiffness helps endure force exerted upon the ankle, ultimately imparting enhanced postural stability [9].

However, a complex relationship between increased ankle stiffness and whole-body balance stability needs to be considered. Perhaps, in addition to the absolute magnitude of the muscle strength exerted from the ankle joint, the degree of freedom of the ankle joint motion (i.e., flexibility) is an important factor that affects dynamic postural stability [10]. This indicates that while taping may positively influence ankle joint’s stiffness through strong support, it may also detrimentally affect ankle joint flexibility. In other words, while an increase in stiffness can be considered positively from the perspective of ankle joint stability, it can also reduce ankle joint flexibility from the perspective of whole-body balance. Reduced ankle joint flexibility can negatively affect knee and hip joints that are systematically connected, and ultimately the overall balance ability [11]. Lower extremity joints are systematically connected, and ankle, knee, and hip joints continuously interact to create an optimal bodily balance [12]. This suggests that a particular resistance or a movement may be required in the knee or hip to compensate for reduced ankle joint flexibility [13]. To conclude, ankle taping that supports ankle joint stiffness may not always be beneficial when attempting to functionally stabilize in static or dynamic movements.

There has been scarce research on the biomechanical effects of ankle taping on postural stability. Most studies have used the center of pressure (COP) to assess postural stability, and COP was derived from sway area and velocity of the whole body [14,15]. For example, ankle taping can provide about 20% smaller COP sway area and 10% slower COP velocity compared with non-taping in people with chronic ankle instability [14]. However, it may be overly simplistic to conclude that ankle taping brings an increased stiffness to the ankle that reduces both the COP sway area and velocity, thereby improving the whole-body balance. Postural stability is achieved through complex interactions between muscular-skeletal systems and nervous systems controlled by the postural control system. These complex interactions entail processing and interpreting movement information, integrating sensorimotor information, and executing appropriate movement to achieve and modulate an erect posture [16]. In summary, a non-linear approach to COP movement patterns and structural analysis that can show postural stability reflective of the complex interactive processes is necessary, in addition to the linear approaches such as COP velocity and sway area analyses.

The objective of this study is to examine the effectiveness of ankle taping on postural stability that reflects COP movement quality in elite Judo players. Both linear and nonlinear analyses were performed to assess postural stability during static postures including three different types of static standings (i.e., narrow, normal, and wide).

2. Materials and Methods

2.1. Participants

A total of twenty-two elite university Judo athletes participated in the study (Age: 22.5 ± 1.7 yr; height: 168.4 ± 7.2 cm, body mass: 74.8 ± 10.2 kg; BMI: 26 ± 2.4; Gender: Female 9, Male 13; Training period, 10.3 ± 1.5 yr; Belt degree, 2.6 ± 0.5). All participants were eligible provided they: (1) are currently affiliated with the Korea University Judo federation and participating in official competitions as Judo players, (2) have experienced ankle taping in their trainings and competitions to prevent ankle injuries, and (3) had no musculoskeletal injuries in the past 6 months. All participants provided informed consent approved by the University Institutional Review Board prior to testing.

2.2. Experimental Protocol

2.2.1. Ankle Taping

For the ankle taping intervention, elastic adhesive bandage taping was applied to all participants. To minimize skin irritation, Mueller 69 mm (Prairie Du Sc, WI, USA) was firstly attached around the ankle joint, and Battlewin tape 38 mm (Nichiban, Japan) was utilized for the ankle taping intervention. A trainer specialized in sports taping conducted taping for all participants. To reproduce the familiar condition of taping, participants and the trainer were mutually communicated during taping application (Figure 1A). The order of taping or non-taping conditions were randomly assigned to all participants.

2.2.2. Postural Trials

For biomechanical evaluation of postural stability, participants were asked to perform three standing tasks including narrow, normal, and wide stance conditions with both taping and non-taping conditions, respectively. Before the standing task, all participants had 15 to 30 min of warm-up time to adapt to the laboratory environment and make their physical conditions similar to the training or competition setting. For the narrow stance, participants were asked to keep their heels together with the toes angled at a comfortable stance of participants. For the normal condition, the feet were kept parallel and 10~15 cm apart depending on height [17], and twice the width of the normal stance was used for the wide stance standing task. For each standing task, participants were asked to stand “as still as possible” for three 30-s trials with their arms comfortably by their side (Figure 1B).

2.2.3. Outcome Measures

For biomechanical postural evaluation, motion trials were performed in a motion analysis laboratory surrounded by an 8-camera optical motion capture system (Vicon, Culver City, CA, USA). Further, we have attached reflective markers on the subject’ lower body based on a plug-in-gait body model. Ground reaction forces (GRF) and moments under the feet for kinetic analyses were collected at 360 Hz using one force plate (AMTI, Watertown, MA, USA) mounted on the laboratory floor level. The COP data were obtained from the GRF and moments data.

For the linear analysis of postural stability, a 95% confidence ellipse sway area (COPSWAY) was calculated around the COP motion along both the anteroposterior and mediolateral axes (Figure 2). Traditionally, a smaller value of COPSWAY indicates greater static balance or postural stability. The details regarding the procedure to calculate the COPSWAY is described in the previous literature [18]. Further, the COP velocity (COPVEL) was computed for the bidimensional COP trajectory (both the anteroposterior and mediolateral directions) [19]. The COPVEL has been suggested to be one of the most sensitive objective measures for detecting changes in postural abilities, a lower COPVEL value indicates good balance whereas a higher value indicates poor balance [20].

We extended the basic evaluation of postural stability by investigating the nature of the control signal using Approximate Entropy (ApEn) which is one of nonlinear measures [21]. By using ApEn which aims to measure structural patterns of COP data in a time series, dynamic stability during static posture was assessed. Based on typical values previously suggested in COP time-series data [22], the vector length and the tolerance range were defined as m = 2 and r = 0.2 of the standard deviation of the time series GRF data. A total of 10,800 data points (30 s 360 Hz) were utilized for ApEn calculations in anteroposterior (ApEnAP) and mediolateral (ApEnML) directions, and the surrogate data test was performed for the reliability verification of the calculated ApEn values [23]. In the extant literature, greater ApEn values were reflective of ‘greater complexity’ and a healthy biological system, whereas less values were denoted as ‘less complexity’ and an unhealthy system [21].

2.3. Statistical Analysis

The sample size was determined based on COP postural measures (primary outcome measure in this study), obtained in a pilot study (n = 6) and calculated on the G-Power (3.1 for Windows), considering a statistical power (β) of 80%. For both taping and non-taping conditions, the mean of three trials for each standing task was used in the analysis. We firstly tested the data normality by checking skewness, kurtosis and histogram, and confirmed that data showed the normal distribution with no outliers. Then, comparisons between means of postural stability variables obtained during taping and non-taping conditions were performed using a paired t-test. Statistical analyses were performed using SPSS 26, and all levels of significance were set at = 0.05.

3. Results

For linear postural measures, significant differences in COPSWAY (p = 0.032) and COPVEL (p = 0.041) in the narrow stance, but no differences in normal and wide stances were observed between taping and non-taping conditions. For ApEnAP of nonlinear measures, significant differences in normal (p = 0.026) and wide (p = 0.014) stances, and a marginal but no statistical difference in narrow stance (p = 0.074) were observed between taping and non-taping conditions. For ApEnML of nonlinear measures, there were no significant differences in all stances between taping and non-taping conditions (

Table 1. Mean, standard deviation and p-value from paired t-tests for all dependent variables including COPSWAY, COPVEL, ApEnAP and ApEnML. p < 0.05 for difference between taping and non-taping conditions.

Postural Variables	Stance	Narrow	p	Normal	p	Wide	p
COPSWAY (cm2)	Taping	1.74	0.025 *	1.79	0.141	1.92	0.521
	Non-Taping	2.32		1.92		2.05
COPVEL (cm/s)	Taping	1.06	0.041 *	1.05	0.685	1.08	0.712
	Non-Taping	1.21		1.09		1.06
ApEnAP	Taping	0.72	0.074	0.79	0.026 *	0.74	0.014 *
	Non-Taping	0.81		0.91		0.95
ApEnML	Taping	0.68	0.467	0.67	0.475	0.65	0.581
	Non-Taping	0.64		0.62		0.62

* Significant difference (p < 0.05) between taping and non-taping. Abbreviation: COPSWAY, 95% Confidence Ellipse sway; COPVEL, COP velocity; ApEnAP, Approximate Entropy Anteroposterior; ApEnML, Approximate Entropy Mediolateral.

).

4. Discussion

The purpose of the current study was to biomechanically examine the effects of functional ankle taping on postural stability in elite Judo players. Particularly, this study used both linear (i.e., COPSWAY and COPVEL) and nonlinear biomechanical postural measures, providing a holistic perspective on how the functional taping intervention influences Judo players’ postural stability.

First, with regard to the linear measures of postural stability, lower COPSWAY and COPVEL values were observed in a narrow stance with a taping condition than non-taping condition. This indicates that ankle taping could limit joint movement, which may in turn increase the ankle joint stiffness. Perhaps, enhanced joint stiffness could strongly support ankle joint, making COP movement smaller while affecting COP’s range in a narrow stance. In other words, this result supports previous research suggesting that ankle taping is effective in enhancing ankle stability by strengthening ankle muscles involved in the ankle movement [2,24].

On the contrary, there were no differences in COPSWAY and COPVEL between taping and non-taping conditions during normal and wide stance standing tasks. Given that the main performance of Judo is to maintain postural stability with wide stance standing [8], our finding suggests that the ankle taping may not be beneficial for improving performance of Judo players. Rather, the ankle taping could suppress the ankle joint movement in a narrow stance, showing lower COPSWAY and COPVEL. This finding may reflect a reduced degree of freedom or flexibility representing an adaptability in various conditions to fluidly control dynamic movements. In other words, it is difficult to explain whether a small or a large value in linear postural measures is good or bad when evaluating the effect of ankle taping on postural stability. Hence, this plausible explanation suggests that only using linear methods of COPSWAY and COPVEL to assess the effectiveness of taping and postural stability may be limited. This is because the definitive value of linear postural measures may not be sufficient to explain postural stability over a certain period of time [25].

Furthermore, we additionally assessed dynamic postural stability of Judo players through a nonlinear method (Approximate Entropy, ApEn). Results indicated that ApEn values in anteroposterior (ApEnAP) were smaller in the overall standing task when ankle taping was applied compared to a non-taping condition. In normal and wide stances, particularly, lower ApEn values were observed in taping compared to non-taping. As previously mentioned, it might be possible that the ankle taping increased ankle stiffness and reduced the degree of freedom of the ankle joint movements. Indeed, observed lower ApEn values in most stance standings may reflect that taping had an adverse effect on flexibility that is necessary for balance control in various dynamic postural conditions [2]. The implication of this nonlinear finding is that reduced ankle flexibility due to taping can have an adverse effect on Judo players who need to adeptly change postures and control those changed postures. In other words, postural complexity is important in fluidly adapting to changing situations. Specifically, the less the postural complexity, the less the flexibility and the greater the consistency in posture control [26]. In summary, taping can negatively affect flexibility that creates COP during fast or slow dynamic movements.

In biomechanical research, non-linear postural analysis has been used to supplement linear analysis to assess postural stability and flexibility. This study used COPSWAY/COPVEL as well as ApEn, both of which are objective measures of body posture stability. Basically, COP movement quantifies how an erect posture is maintained, utilizing measures for postural stability between the surface and the body by assessing postural sway and velocity. Ultimately, COP is considered a definitive value that provides information on how ankle’s sensory receptors directly affect postural sway and stability. Traditionally, smaller COP fluctuation was considered to reflect stability and COP fluctuation being affected by aging or physical environments [27]. However, using only one quantifiable value to assess the overall bodily stability may not be sufficient because controlling bodily movements is a result of dynamic interactions between musculoskeletal and neurological systems [28]. Thus, it should be noted that the effectiveness of a functional ankle taping intervention to enhance body posture system derived from a simple quantitative analytic method is limited.

Despite the limitation, this study has several strengths. There are scarce biomechanical literature that have examined the effects of ankle taping on postural stability in elite Judo players. This study is the first study that utilized both linear and nonlinear measures to explore how ankle taping affects Judo player’s postural control. Through linear analysis, we quantified how ankle taping affects stability during a static posture; through nonlinear analysis, we sought to understand how ankle taping affects flexibility (that influences postural balance) by quantifying postural complexity. Most importantly, this study suggests that ankle taping purported to increase ankle stability may ironically negatively affect posture maintenance. Of course, this study does not contradict previous research suggesting that ankle taping reduces the possibility of ankle injury during dynamic movements through strengthening fibula and increasing proprioceptive sensibility [3].

5. Conclusions

Given the biomechanical perspective that taping intervention may strengthen joints, ankle taping has long been used to prevent injuries and to increase postural stability. However, the current study demonstrated that a stiffened ankle joint fixed by taping could have negative effects on ankle flexibility and overall postural stability in Judo players. In this regard, our study suggests that the purpose of ankle taping should be reconsidered and associated individual objective data should be first analyzed before taping application.