Dance is the body’s response to the feelings created by a particular situation and can be said to be the most basic form of expression for humans (Jang, 2007). The jumping movement in dance is an essential part of every piece and as a basic movement technique, makes possible various forms of expression (Choi, 2001). According to advanced re- search, it is apparent that the foot type affects how the jumping tech- nique was performed (Yoo, 2015). The shape of the foot can be divided into three forms according to the height of the medial arch: pes rectus, pes cavus, and pes planus. Among the pes planus form, there is a flexible pes planus that occurs due to the over-pronation through weight-bearing (Kadakia & Haddad, 2003; Ker et al., 1987), and a rigid pes planus (Rodriguez, Choung, & Dobbs, 2009). That has no relation to weight-bearing. The inner arch of the foot is higher, and has a more flexible and elastic structure than the outer arch, and it plays an important part in absorbing the impact upon touching ground (Park, 2008; Richie, 2007). Furthermore, being the primary support structure for weight-bearing, the inner arch of the foot plays an important role in absorbing impact during various movements, such as walking or running (Nawoczenski & Flemister, 2006).

There are various treatments for the collapsed arch in the case of pes planus (Jacobs, 2007), but among them, the taping method has the positive sides of being economical, convenient and standardized (Kim, 2011). Recently there have been many studies where elastic bands have been used, but they have been limited to determining the use of the elastic bands and to physical workout programs. The inner arch support band has been produced in two structures by grafting the taping method for holding the inner arch of the foot onto the elastic band.

Thus, the purpose of this study establishes the differences of ground reaction force variables and relative sensations according to the second position vertical jump in ballet.

1. Participants

The subjects of this study were made up of 12 ballet majors who have danced professionally for more than ten years (age: 24.33±2.96 years, height: 165.33±3.75 cm, weight: 49.83±4.47 kg). Before the experi- ment, the purpose of the research, the sequence of the experiment and movements were explained to the subjects and after confirming intention to participate and receiving consent forms, the experiment was carried out.

2. Variables

In this research, the independent variables were the foot type (pes rectus: ±2°, pes planus: <±3°) and the structure of the inner arch sup- port band (no band, linear shaped, x-shaped). The inner arch support bands used were the linear shaped band used in Lee's 2016 study and the x-shaped band which has a structure with a wider area that helps prop up the arch. Furthermore, in the Low-dye taping method, only the method of the sixth stage, offering lifting support to the arch was chosen. The displacement control of the used support bands was 50 mm/min, the tensile strength 12.92 MPa, and the fracture elongation 928.7% (Figure 1).

Figure 1. Structure and features of the inner arch support band

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The dependent variables were ground reaction force variables and sensations according to phases.

The ground reaction force variable (Table 1, Figure 2) measured the right foot using the force platform (Kistler, 9281B, Switzerland).

Figure 2. Ground reaction force variables

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3. Measurement

The necessary experiment equipment for this research could be found at the E University gymnasium's dynamics laboratory, located in Seoul. First, the foot type of each subject was measured. After doing some light stretching to perform the jumping technique properly, the subjects began the experiment. To ensure consistency during every movement, the movements were carried out matching the 3/4 time 120 tempo (Allegro) of the metronome. Having divided the inner arch support bands into no band, linear-shaped band and x-shaped band, each was measured three times, all together nine times. Only the right foot was measured, but the movements were performed while wearing the bands on both feet.

4. Data Processing

This research analyzed the three phases of the second vertical ballet jump, the take-off, the flight extensive and landing phase (Figure 3).

Figure 3. Three phases of the second vertical ballet jump

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5. Statistical analysis

Data processing utilized Windows IBM SPSS Statistics 22.0. To measure the ground reaction force variables differences according to the foot type the structures of the inner arch support bands, and, wearing sen- sations according to the structures of the inner arch support bands, a one-way ANOVA was carried out. Statistical level of significance was set at p<.05 and post hoc analysis was conducted using Bonferroni correction.

1. Difference in ground reaction force according to foot type

The extensive impulse during landing (F=5.04*) according to foot type was significantly bigger in the case of flexible pes planus (94.13, ±16.65) than pes rectus, however other variables did not reveal statis-tically significant difference (Table 2).

2. Difference in ground reaction force variables according to inner arch support band structure

According to the results of the one-way ANOVA, the time required according to the structure of the band (F=6.01**) was significantly longer when wearing an x-shaped band (1.20, ±.05) than when the subject was not wearing a band (1.13, ±.05). The take-off time required (F=12.29***) was significantly longer for the linear-shaped band (.45, ±.03) and the x-shaped band (.46, ±.05), when compared to no band (.40, ±.00). The landing phase time required (F=4.11*) was significantly longer for the x-shaped band (.42, ±.04) when compared to no band (.38, ±.03). The active maximum force during landing (F=7.85**) for the x-shaped band (519.52, ±82.25) and linear-shaped band (593.13, ±192.89) was significantly smaller than with no band (751.74, ±141.91). The flexive impulse (F=7.64**) for the x-shaped band (15.10, ±8.01) and the linear-shaped band (17.04, ±8.37) was also significantly smaller than for no band (27.84, ±9.37). However, for the flexive impulse (F=3.83*) for the x-shaped band (36.23, ±11.93) was significantly higher than that of no band (25.50, ±5.90). On the other hand, during the take-off phase flexive section's active loading rate, flexive section's active impulse, active maximum force, extensive section’s active decay rate, extensive section's active impulse, Z-Y maximum force time difference, Z-X maximum force time difference, required time for flight, number of passive peaks, pas- sive loading rate of heel, extensive impulse, extensive impulse there was no significant difference (Table 3).

3. Survey regarding wearing sensation, jumping sensation, and landing sensation

The wearing sensation according to structure of band (F=3.46*) was significantly higher for the linear-shaped band (3.75, ±.45) than no band (3.25, ±.45). Jumping sensation (F=6.95**) was significantly higher for the linear- (3.75, ±.45) and x-shaped bands (3.92, ±.67) than with no band (3.17, ±.39). Landing sensation (F=18.53***) was significantly higher for the x-shaped band (4.25, ±.62) than for no band (2.83, ±.58) and linear-shaped band (3.42, ±.51) (Table 4).

The extensive impulse during landing according to the foot type was significantly bigger for flexible pes planus than for pes rectus (Kim, 2013). This shows that the extensive impulse during extension is bigger for pes planus than for pes rectus, and within pes planus it is bigger for rigid pes planus than for flexible pes planus. This kind of big extensive impulse means flexing down, and because of this, instead of lightly rising, the movement might appear more sluggish. When connecting it to the next movement, the ability to lightly and gracefully link the movements is reduced. Thus, it is recommended, especially for flexible pes planus, to use inner arch lifting bands during training or perfor- mances to overcome the posterior tibial tendon dysfunction with pes planus (Erol et al., 2015, Kohls-Gatzoulis et al., 2004).

The total time required, take-off time required, landing time required according to the structure of the band were all significantly longer for the x-shaped band than for linear-shaped band or no band. The longer time required during the time-limited performance experiment means that the jumps performed by subject with x-shaped bands were high and graceful (Linthorne, 2001).

During landing the active maximum force was significantly lower for the x-shaped band and the linear-shaped band than for no band (Lee & Hong, 2005). The flexive impulse, as well, was significantly lower for the x-shaped band and the linear-shaped band than for no band (Chen, 2011; Chiu & Wang, 2007).

However, the flexive impulse was significantly higher for the x-shaped band than for no band. The x-shaped band reduces the impact, helps with progressing the active force in the flexive phase and contributes to a light descent.

The x-shaped band showed the longest time required for pes rectus in the difference in the ground reaction force according to the shape of the foot and structure of the band (Linthorne, 2001). The impact that occurs during landing was statistically significantly reduced when x-shaped bands were worn on pes rectus and rigid pes planus. The impact was lowest for flexible pes planus when linear-shaped bands were used. This shows that both types of bands reduce impact and that there is a difference in which band structure reduces the impact according to the shape of the foot.

Jumping sensation was significantly higher for the linear and x-shaped bands than with no band. Landing sensation was significantly higher for the x-shaped band than for no band and linear-shaped band.

The purpose of the vertical jump in dance is to leap high and land lightly. The function of the interior arch lifting elastic bands is to extend the time required for take-off and enlarge the manifestation of active force, as well as reduce impact during landing. Furthermore, impact was not only reduced for rigid pes planus, it was also reduced when interior arch lifting elastic bands were used on pes rectus. The x-shaped bands are effective for pes rectus and rigid pes planus, while linear-shaped bands are effective for flexible pes planus. Thus, regardless of foot shape, arch lifting elastic bands are essential for jumping training in dance.