Taekwondo is a sport where the outcome of the match is determined by using the limbs of the body to strike the opposing player and earn points (Jeong et al., 2019). The attacking techniques of taekwondo are categorized into those either using the hands or feet. In particular, the movements of the lower limbs during competitive matches are repetitive and complex in a short span of time (Slimani et al., 2007). The complex movements in taekwondo consist of many functional forms such as the double kick, direction-change, footwork, and roundhouse kick, and these movements are mostly adjusted and controlled by the feet. As a result, there are several cases of injuries in the lower limbs of the athletes. Repetitive injuries can lead to chronic ankle instability, causing a decrease in flexibility, strength, balance, and proprioceptive sensibility.

The foot movement from the taekwondo athletes requires support from the standing foot, footwork-skill from the kicking foot, and stability and balance to maintain posture (Son et al., 2018). These movements are centered around the ankle and as a result, they can lead to restrictions in the joint’s range of motion (ROM), muscle weakness, and decrease in proprioception sensibility, eventually leading to ankle instability (Sekir et al., 2007). Additionally, the unique footwork, jumps, and landing in taekwondo cause repetitive supination and pronation, leading to shortening of the Achilles heel and weakness in the tibialis anterior and peroneus muscles, thus hindering the balance of the feet. The chronic ankle instability comprises 40%–50% of the lower limb injuries (Bridge et al., 2014; Fong and Ng, 2011).

Chronic ankle instability has a clear impact on the muscular strength of the ankle, therefore, training regimes focus on the strengthening of these muscles around the ankle. However, recent research has shown that if the ROM and flexibility in the ankle are not recovered first, then it is difficult to strengthen the muscles around the ankle and the reoccurrence rate of the same injury also increases (Flores et al., 2011). Additionally, the recovery of the ankle’s ROM helps to stimulate the proprioception and muscle contraction of the ankle, accelerates the rotational speed, and increases the muscular strength of the ankle (Schwesig et al., 2016). As a result, the recovery of a healthy ankle ROM has a correlative relationship with the muscular strength of the ankle (McKean and Burkett, 2009).

The application of instrument-assisted soft tissue mobilization (IASTM) on an ankle affected by the chronic ankle instability, stimulates cellular reconstruction of the infection, tendon, muscles, and other tissue structures in the area (Ikeda et al., 2019). Additionally, IASTM can alleviate pain associated with the muscle and ligament, promote regular ROM, and structurally and functionally treat the damaged area (Cheatham et al., 2016). Overall, IASTM has a positive effect on the nervous system and body function of the specific area (Seffrin et al., 2019). However, in the current state of scientific research, inadequate research has been done on the use of IASTM.

Thus, we investigated the effects in ROM, isokinetic strength, balance by applying IASTM rehabilitation exercise. We providing data for precise and appropriate chronic ankle instability rehabilitation exercise.

Excellent performance of taekwondo requires balance, flexibility, and muscle power of the body. Flexibility among those factors has a lot of connections to performance (Dupont et al., 2004). However, excessive flexibility of the ankle increases the injury of the ankle (Jovanovic et al., 2011). In particular, chronic instability of ankles showed D/F reduction and P/F increase (Simone et al., 2019). There was a significant difference in the dorsal and plantar-flexion of the taekwondo athletes between the control and rehabilitation groups after the IASTM rehabilitation (right P/F, F=16.200, P< 0.001; right DF, F=6.974, P<0.01; left P/F, F=36.922, P<0.000; left D/F, F=36.481, P<0.000). Similar results have also been reported by Terada et al. (2013), who reported that the use of the muscle relaxation technique helped stimulate the conglutinated area of the ankle, improve the ROM, and alleviate pain by releasing the structural pressure of the affected area in individuals with feet pain and a restricted ROM in the ankles (Imai et al., 2015). Additionally, this technique created microinjuries in the conglutinated area to stimulate the recovery of the area and positively affected the ROM in the ankles. Another study conducted by Schaefer and Sandrey (2012) distributed chronic ankle instability participants into three groups (Graston Tech. group, dynamic stretching group, and control group) for a total of 3 weeks. In this regard, results of this study reported that compared to the dynamic stretching group, the Graston group and dynamic stretching group had improvements in balance and ankle function through the restimulation of the ligament where the fibroblast recovery phase was halted. In addition, these improvements of ankle function provide ankle stability for chronic ankle instability players (Simone et al., 2019). As a result, the precedent studies corroborate the findings in this study and the following results show that IASTM can be effectively used to improve the ROM of the ankles through the stimulative recovery of injured ligaments and muscles causing chronic ankle instability in taekwondo players.

Isokinetic muscular strength is generated from a constant speed and specific motion and is a fundamental muscular strength required by every athlete (Dauty et al., 2016). It also interacts through movement to represent stability. In taekwondo athletes, the center of gravity is placed in the forefoot of both feet and the excessive use and exhaustion of the soleus, gastrocnemius, tibialis anterior, and long peroneal muscles can cause muscle tension and an impairment in the ROM, thereby leading to a decrease in muscular strength (Giulio et al., 2009). Hertel (2002) showed that the severity of chronic instability can increase due to repetitive injury; however, constant stimulation of ankle joint muscles can lead to an increase in muscular strength and improvement in mobility. Thereby, increasing the stability of the ankle. In this study showed that there is a significant difference in the isokinetic ankle joint muscular strength between the IASTM rehabilitation and control groups (in plantar-flexion, at the right and left-foot angular velocities of 60°/sec, F=28.479, P<0.0001, F=66.568, P<0.0001; 180°/sec, F=42.635, P<0.0001, F=58.744, P<0.0001; in dorsiflexion, 60°/sec, F=38.800, P<0.0001, F=39.533, P<0.0001; 180°/sec, F=55.462, P<0.0001, F=27.927, P<0.0001). A precedent study conducted by Van den Tillaar and Ettema (2009) reported that there is a correlative relationship between the angular speed of rotation, muscular strength, and ROM in the ankle. These results are consistent with those of the present study, and as a result, a muscle relaxation technique can improve the ROM and muscular strength of the ankle, and stimulate the movement in the ankle to improve muscular mobilization. Thus, it was assumed in this study that the constant stimulation and improvement in the ROM played a role in the improvement of the isokinetic muscular strength in the ankle.

For taekwondo athletes, balance is established through minimizing the standing posture and base surface and maintaining a high center of gravity (Brachman et al., 2017). When a kick is performed, the proprioceptive senses are required to control the movement of the body (Fong and Ng, 2011; Han et al., 2015). This study showed that there was a statistically significant difference in the ability to balance between the rehabilitation and control groups. According to precedent studies, an impairment in the sensory capability can also impair balance (Pasma et al., 2015). A study by Mecagni et al. (2000) investigated the relationship between the ROM in the ankles and ability to balance and showed that ankle exercises improving its ROM also influenced the ability to balance and prevent further injuries. Additionally, a study investigated the relationship between the ROM in the ankles and lower muscular strength with static eye open balance and found that static balance is determined by stability of the ankles, which is affected by the muscular strength and ROM of the ankles (Kim and Kim, 2018). These results correspond to those of a previous study that reported that the balance of SEO and SEC has higher and PS increase, which improves body balance. Balance ability in the body of the IASTM group participants significantly improved as follow: in SEO (F=22.983, P<0.0001), SEC (F=39.663, P< 0.0001), and PS (F=4.847, P<0.05). It is believed that the significant difference found in the rehabilitation group in this study can be explained by the indirect improvement of balance through the improvement in the ROM and proprioceptive senses of the ankles. Based on these results, an IASTM rehabilitation exercise program can improve ankle balance, and to maintain this improve, it would be necessary to using the IASTM exercise program continually during the training in chronic ankle instability taekwondo players.

In this study, the IASTM rehabilitation exercise improved the ROM of ankle joint, isokinetic muscle strength, and balance of the chronic ankle instability taekwondo players. Thus, sustained use of an IASTM rehabilitation exercise is determined necessary for improving ankle instability and effective athletics care in not only young taekwondo players but also other age in chronic ankle instability athletes. As with any study, there are minor two limitations in this study. First, because the subjects were recruited from one high school in South Korea, they do not represent the entire Korean taekwondo players. In addition, the subjects comprised a limited number of high school students (N=20). Second, because various training methods and rehabilitation techniques are applied to each person through IASTM it is difficult to conclude that exactly the same treatment exercise has been applied to all the taekwondo players.