PRESSURE EVALUATION OF SEAMLESS YOGA LEGGINGS DESIGNED WITH PARTITION STRUCTURE

determined the allowable pressure range of the human body based on the sensory analysis of female participants. At present, the structural design of yoga clothing on the market is chaotic, which cannot effectively protect the stretching and deformation of muscles in yoga exercises, or produces Abstract: It is a novel approach to design the partition structure of clothing according to the deformation of the human body surface skin during exercise. The functional evaluation of these products remains unknown, and there is limited knowledge about the effects of the partition structure design on the pressure comfort of clothing. This research carried out a partitioned structural design of the leggings based on the skin deformation of the lower limbs of the human body during yoga exercise and developed two styles of seamless yoga leggings. The skin pressure exerted by the new seamless yoga leggings was compared with two commercial yoga leggings. Eight female college students were invited to wear all the yoga leggings samples and perform yoga exercises. The skin pressure exerted by yoga leggings was measured by the German novel-Pliance multipurpose pressure distribution measurement system on 10 body positions. The results showed that yoga leggings designed with a partitioned structure exert a comfortable pressure on the skin during yoga exercise, and the pressure change was smaller under different yoga postures, which has better pressure stability. The partition structure design model of seamless yoga leggings was optimized, which provided a reference for the functional partition design and product development of seamless yoga leggings.


Introducton
As a fashion sport, yoga has attracted more and more people to participate and promoted the development of the yoga clothing market [1,2]. In sportswear, pressure comfort is the most important performance, which will affect the wearer's sports performance and efficiency. Free movement and no sense of restraint are the standards for the structural design of sportswear. The characteristics of sports items and human body structure should be considered in the style design [3]. Zhou et al. [4] designed clothing styles and determined patternmaking parameters according to the skin deformation of key parts of the human body in the climbing posture and selected appropriate fabrics to make mountaineering clothing and try on. Feng and Wang [5] constructed a model of football tights and provided a basis for the loose weight of football tights by studying the skin deformation of men's lower limbs in football postures and combining the physiological structure of the human body. Gao [6] optimized the structure of the tight shorttrack speed skating suit according to the characteristics of human skin deformation in short-track speed skating. Cheng and Kuzmichev [7] unify the morphological features of the male torso and underwear construction into a universal system of virtual underwear design，which have improved the method of underwear design, making the underwear more comfortable and suitable for individual morphological features. By exploring the characteristics of the human body in the state of exercise, designing clothing styles, and setting loose weights, the pressure comfort of the clothing can be improved.
Clothing pressure is the result of the interaction between clothing and the human body. As an important indicator for evaluating clothing comfort, it has become a research hotspot in the clothing industry. Wang et al. [8] calculated the pressure comfort threshold distribution of the female upper body based on psychophysical limit-step method. Zheng et al. [9] evaluated the pressure of the newly developed seamless bra and commercial bra and established an empirical equation for predicting the pressure of the bra. Kuzmichev et al. [10] determined the allowable pressure range of the human body based on the sensory analysis of female participants.
At present, the structural design of yoga clothing on the market is chaotic, which cannot effectively protect the stretching and deformation of muscles in yoga exercises, or produces

Abstract:
It is a novel approach to design the partition structure of clothing according to the deformation of the human body surface skin during exercise. The functional evaluation of these products remains unknown, and there is limited knowledge about the effects of the partition structure design on the pressure comfort of clothing. This research carried out a partitioned structural design of the leggings based on the skin deformation of the lower limbs of the human body during yoga exercise and developed two styles of seamless yoga leggings. The skin pressure exerted by the new seamless yoga leggings was compared with two commercial yoga leggings. Eight female college students were invited to wear all the yoga leggings samples and perform yoga exercises. The skin pressure exerted by yoga leggings was measured by the German novel-Pliance multipurpose pressure distribution measurement system on 10 body positions. The results showed that yoga leggings designed with a partitioned structure exert a comfortable pressure on the skin during yoga exercise, and the pressure change was smaller under different yoga postures, which has better pressure stability. The partition structure design model of seamless yoga leggings was optimized, which provided a reference for the functional partition design and product development of seamless yoga leggings.
a sense of restraint and pressure during large movements [11]. It is necessary to divide the human body into different areas according to the characteristics of the human body movement in yoga exercise. Then, the clothing is designed with a reasonable structure division to make it more suitable for human wearing comfort [12].
In this study, we designed the partition structure of the clothes based on the skin deformation of the lower limbs of the human body during yoga exercise and used seamless technology to develop new knitted yoga leggings. We evaluated its pressure comfort compared with commercial yoga leggings. The design principles for further development of seamless yoga leggings are proposed.

Skin deformation of the lower limbs of the human body during yoga exercise
In yoga exercises, body movements are basically produced by joint movements, which correspondingly drive changes in muscles, subcutaneous fat, and body surface skin, and they are fi nally refl ected in the stretching and deformation of body surface skin [13]. By measuring the skin deformation data of the lower limbs of the human body during yoga exercises, the skin deformation map of the lower limbs is drawn and applied to the partition structure of yoga leggings.
In the yoga postures, the lower limbs movement takes the femoral and the knee joint as the two major fulcrums, and they have a certain range of activity. We classifi ed and The VITUS Smart XXL three-dimensional scanning system (Human Solutions, Germany) was used to scan and record the three-dimensional human body images of the subjects under standard standing and yoga postures. We used ScanWorX software to measure the horizontal and longitudinal lengths between the marked points, and fi nally, we calculated the rate of skin change on the body surface according to the dynamic and static change rate formula. % 100 Where L 2 refers to the length between the marked points under the yoga action, and L 1 refers to the length between the marked points in the static standing state.
Due to the difference in skin deformation of the same part under different yoga postures, in order to make the clothing meet the pressure comfort requirements, it is necessary to ensure that the clothing pressure under the largest skin deformation is still in the comfortable pressure range. The maximum value of skin changes under fi ve yoga postures is selected, and the data grading method is used to divide the skin deformation values to obtain a grid map of lower limb skin changes in yoga postures, as shown in Figure 1.

Knitting and performance testing of fabrics
In the knitting of fabric, 78dtex nylon and 30D pure Spandex yarn, which are commonly used in high-elastic clothing, were selected. Among them, spandex is the ground yarn, and nylon is the veil. We used the Santoni seamless underwear circular knitting machine (SM8-TOP2 MP2) to knit fi ve kinds of fabric structures commonly used in seamless garments, as shown in Figure 2.
We measured the tensile force of the fabric under constant elongation in the longitudinal direction by the YG028 Electronic Fabrics Strength Tester (Ningbo Textile Instrument Company). The elongation is set to 10%, 20%, 30%, 40%, and 50%, which corresponds to the skin deformation rate of the lower extremities ( Figure 1). The results are shown in Table 1. According to the cluster analysis method, the fabric structure is classifi ed, and the fi ve types of fabric structures are divided into three categories, namely low-stretch fabrics: 3 and 4; mediumstretch fabrics: 2, 5; and high-stretch fabrics: 1.

Knitting of yoga leggings samples
The style of seamless knitted yoga leggings is shown in Figure  3. Style 1 is to divide the clothing area according to the skin deformation map of the lower limbs of the yoga exercise human body. The division line is used to distinguish the different skin deformation areas, and the physiological structure of human body is considered in the setting of the division line. In order to increase the control group, the waist and tie-up design of style 2 is the same as that of style 1, and the other areas are not designed for zoning.
To make the clothing have good body-fi tting and pressure comfort, the clothing fabric should be adapted to the expansion and contraction of the skin surface of various parts of the human body as much as possible [14]. When the fabric is deformed by an external force, the skin pressure exerted on the human body is still in the comfort zone and fl uctuates within a certain range. Therefore, the different fabric structures in various areas of the clothing are applied, so that the tensile properties of the fabric structure in each area of the clothing form a level change, which corresponds to the skin deformation. Knit an easy-to-stretch structure in the area where the skin deformation exceeds 30%, that is, high-elastic fabrics. Use medium-elastic fabrics in the 10%-30% deformation area, and low-elastic fabrics in the area where the deformation is less than 10%, to ensure that the stretching force of each part of the fabric tends to be consistent when stretched. Combining the forming principle of seamless clothing, the fabric structure of the clothing is shown in Figure  4. The waist and ankle ties are all made of false ribs. Style 2 is made of high-elastic fabrics as a whole. The garment is knitted with Santoni seamless underwear circle (SM8-TOP2MP2). The gray fabric of the off-machine is stitched at the mouth of the tube for fi nishing, and fi nally it is cut and stitched. The fi nished product is shown in Figure 5: sample 1 is style 1, and sample 2 is style 2.

Selection of commercial yoga leggings
In order to evaluate the comfort performance of the newly developed seamless yoga leggings, two commercial yoga leggings of the same size were selected for comparison, as shown in Figure 6. Sample 3 uses a knitted fabric (NuluTM) for traditional cutting and sewing, and the fabric of this sample has better elasticity than other samples (sample 1, sample 2, sample 4). Sample 4 uses nylon and spandex as raw materials, uses seamless technology for knitting, and the elasticity of this sample is less than that of sample 2 and sample 3. The styles are similar to the newly developed seamless yoga leggings, but there is no regional knitting design of fabric structure for clothing.
In order to reduce the infl uence of clothing size on the experimental results, the sizes of four leggings were measured. The results are shown in Table 2. The sizes of the four leggings human body is shown in Figure 7, and their defi nitions are given in Table 4 [15,16].
The German novel-Pliance multipurpose pressure distribution measurement system was adopted, as shown in Figure 8. The measurement system is equipped with capacitive sensor, and the sensitive components in the sensor are highly accurate and can accurately measure the pressure distribution of the threedimensional surface. The subjects practiced yoga movements on a yoga mat, became familiar with the movements, They then wore yoga leggings to maintain a standard standing posture and practiced fi ve yoga movements, as shown in Figure 9, and are relatively close, and the difference in size of the same part is not more than 3 cm.

Human subjects
Eight female college students with a height of 160-165 cm were recruited as experimental subjects, with an average age of 23.8 years and an average weight of 51.2 kg. The average circumference of their lower limbs is shown in Table 3.

Yoga leggings pressure evaluation
In this study, eight subjects all wore two newly developed seamless yoga leggings and two commercial yoga leggings for pressure evaluation. With reference to the literature on trouser pressure and the characteristics of human movement in yoga exercise, a total of 10 points were selected for pressure evaluation, and the location of the measurement points on the    pressure [17]. In Figure 10, points A and F have smaller pressures relatively in all the measurement points，less than 0.6kPa. This is because the curvature of the hips and knees of the human body is large, resulting in a small fi t between the clothing and the human skin. The pressure at points I and J are relatively high, just right at the calf. It may be that the muscles of the calf are raised and the circumference increases, which makes the clothing pressure at this place larger. The pressure of the four samples at points B, C, and D (hip line) are quite different, especially the pressure of sample 4 is signifi cantly lower than other samples, which indicates that the fabric has a greater impact on the pressure of the hip area.
adjusted their body postures through a protractor to ensure the standard and consistency of yoga movements. Single sensors were used to measure the pressure at the points on the body for three times. Time pressure data was continuously collected for 60 seconds. Twenty pressure measurements per second were recorded. Figure 10 shows the average pressure of eight subjects at each measurement point. The clothing pressure at the measurement point is between 0.2 kPa and 1.2 kPa, and less than 1.96 kPa, which are in the comfortable range of tight-fi tting clothing  Overall, the pressure range of sample 3 is the smallest, followed by sample 2, and the pressure range of sample 4 is the largest, exceeding 2.0 kPa. The pressure of measurement point of sample 3 has the smallest change during yoga exercise, while sample 4 has the largest fl uctuation, which indicates that the tensile properties of clothing fabrics are an important factor affecting clothing pressure, and the better the tensile properties, the more stable the clothing pressure during dynamic sports. The newly developed yoga legging has higher pressure at point A (outer waist) and point D (buttocks), because the waist is one of muscle belt and fat center belt in the adult female body. Waist movement causes skin compression and muscle squeeze to protrude, which increases pressure on clothing, and the new yoga legging has a knitted fake rib on the

Pressure of yoga leggings under yoga exercise
Yoga is a static exercise. Practitioners need to coordinate body movements on a static and natural basis and maintain a posture for a long time. Therefore, we analyzed the clothing pressure while the human subjects maintaining the yoga posture to evaluate the pressure comfort performance. Figure  11 shows the pressure at the measurement points on subjects wearing four samples during yoga exercise. The pressure at each measurement point are the average of eight subjects.

Pressure of newly developed and commercial yoga leggings
Since the newly developed seamless yoga legging (sample 2) and commercial yoga leggings (sample 3, sample 4) have a similar structural design, the overall clothing uses fabrics with the same fabric structure, so it was chosen for comparison with waist, which increases the thickness of the garment. So it has a higher pressure than other samples. In posture 5, the pressure of points H, I, and J (knee and calf) reach the maximum. When the knee is bent, the skin stretches and deforms greatly, the calf muscles are in a tight state, the clothing produces stretch deformation to adapt to the skin deformation, and the pressure on the skin increases.

Pressure of two newly developed yoga leggings
The two newly developed yoga leggings are made of the same yarn and machine. Sample 1 is designed with a partition structure, and sample 2 is knitting with a fabric structure. Therefore, the two samples are compared.
The pressure of the two samples is less than 1.6 kPa. In posture 1 and posture 5, points D (hip), H, I, and J (knee and calf) are where the pressure fl uctuates greatly. The pressure of sample 1 is less than sample 2 and is closer to the pressure under other postures, which shows that clothing designed with a partition structure has lower pressure changes during yoga. Figure 12 shows the pressure change rate at each measurement point of the subjects wearing four samples during yoga exercise, which are the average values of eight subjects.

Pressure change of newly developed and commercial yoga leggings
In samples 2, 3, and 4, overall, the pressure change rate of sample 3 is the smallest, and sample 4 is the largest. This shows that improving the elastic properties of clothing fabrics can reduce the pressure changes exerted by clothing on the human body during dynamic movements. Among the 10 measurement points, the pressure change rate of point A is the highest, because yoga mainly exercises around the spine. The waist can perform movements of different amplitudes and angles through the twisting of the spine and other movements, which makes the clothing exert pressure on this part to produce obvious changes under different yoga movements [18]. At points H (knee circumference), I, and J (calf), the clothing pressure increases significantly due to the bending of the knee, and the pressure change rate is the largest among the five yoga postures. Point F is located on the lower side of the buttocks, because the buttocks are round and protrude backward, there is a gap between the clothing and the human body, and the contact area between the sensor and the human body is unstable, which makes the pressure at the measurement point change greatly.

Pressure change of two newly developed yoga leggings
The clothing pressure change rate of sample 1 and sample 2 are relatively similar. On the whole, the pressure change rate of sample 1 is less than that of sample 2. Except for point A and point H, the pressure change rate of other points is less than 30%, which indicates that the partition-structure-designed yoga leggings have a small range of changes in the skin pressure exerted on the human body during yoga exercises and have better pressure stability.

Clothing pressure comfort evaluation of yoga leggings
The pressure value is one of the standards to evaluate the comfort of clothing pressure [19,20]. During exercise, the smaller the pressure change caused by the deformation of the fabric, the smaller the pressure change rate. The pressure exerted by the clothing on the human body fluctuates in a small range, and the wearing comfort of the clothing is higher. In order to better evaluate the pressure comfort performance of yoga leggings, according to the pressure value and pressure change rate of the measurement point under the yoga action, we combined the cluster analysis method, the assignment method, and the function evaluation method to make a comprehensive evaluation of the four yoga leggings.

Classification and assignment of clothing pressure
In the subjective evaluation of clothing pressure comfort, the five-level interval scale method is often used for scoring to quantify subjective feelings. In the objective pressure test, the pressure values of different sample measuring points are distributed widely and irregularly. In order to facilitate analysis and evaluation, the pressure values and pressure change rates of the measuring points are clustered and analyzed. Refer to the subjective comfort evaluation method, divide the pressure value and the pressure change rate into five intervals, and use the assignment method to assign a certain value to the classification interval [21,22]. During the objective pressure process, eight subjects made a subjective evaluation of the comfort of the measuring point. When the pressure value is 0.8-1.0 kPa, they feel the most comfortable. Therefore, this interval is assigned a value of 5, the interval is taken as the midpoint, and the assignments on both sides decrease. In the pressure change rate, the smaller the value, the larger the value assigned. The results are shown in Table 5.

Establishment of functional evaluation value
To

S S
Where S kj is the function evaluation value of sample K at measuring point J, S ij is the value of posture I at measuring  point J, k is 1-4 samples, j is a total of 10 measuring points A-J, and i is six postures.
According to formula 1, the function evaluation values of 10 measuring points of four samples were calculated, as shown in Table 6 and Table 7 .
From the analysis of the pressure value, the function evaluation values of different samples were arranged in descending order: samples 3, 2, 1, and 4. That is, for yoga leggings, the better the fabric elasticity, the better the overall pressure comfort of the garment. From the analysis of the pressure change rate, the functional evaluation values of different samples were arranged in descending order: samples 1, 3, 2, and 4. That is, clothing designed with a partition structure has the best pressure stability in yoga.
It can be seen that in the production of yoga leggings, fabrics with good elasticity are used, and the clothing pressure values of different parts of the human body are the closest.
In yoga leggings designed with a partitioned structure based on the deformation of the human skin during yoga exercise, the elasticity of the fabric in different clothing areas forms a gradient change, which corresponds to the deformation of the skin. In yoga, clothing pressure changes the least, basically fl uctuating in a stable small range. Therefore, determining the elasticity of the fabric according to the skin deformation can improve the pressure comfort of the garment, but it is not suitable for some areas.

Elastic distribution of partition structure design of seamless yoga leggings
Taking the garment structure of sample 1 as the optimization object, in the measurement points (D, E, F, H, I), highelastic fabric (fabric 1) is used in the area of points F and H, and medium-stretch fabric is selected at point D (fabric 5). Choose low-stretch fabrics (fabric 4, fabric 3) at points E and I. Among the measuring points (B, C, J), sample 2 has a higher functional evaluation value, and the high-elastic fabric (fabric 1) is selected. Among the measurement points (A, G), sample 3 has the highest functional evaluation value, and the elasticity of the fabric used is better than that of samples 1 and 2. The fabric elasticity with the maximum functional evaluation value at 10 measuring points is integrated, and the fabric elasticity demand of the partition structure of seamless yoga legging is optimized, as shown in Figure 13.
It can be seen from Figure 12 that the waist and the front of the thigh have the highest requirements for fabric stretch performance, followed by the abdomen, the outside of the hip line, the back of the calf, the front of the knee, the back of the thigh, and fi nally the hips, the inner thigh, and the front of the calf.
The waist belongs to the center point of muscle belt and fat, which is easy to cause muscle squeezing. It is necessary to choose soft and elastic fabrics and reduce the thickness of the fabrics as much as possible. Moreover, the waist can move in multiple angles with a large range. It is necessary to further divide the waist area and study the needs of different regions for fabric elasticity.

Conclusions
In this paper, the trouser was designed with a partition structure based on the skin deformation of the lower limbs of the human body during yoga exercise, and two seamless yoga leggings have been developed. The clothing pressures of two newly developed yoga leggings and two commercial yoga leggings were measured on 10 body positions of 8 subjects. The main conclusions are as follows: The newly developed seamless yoga leggings exert skin pressure on different parts of less than 1.6 kPa. Compared with commercial yoga leggings, yoga leggings designed with a partition structure have a more stable pressure value during dynamic movement, which shows that the newly developed seamless yoga legging provides better comfort for the wearer.
A design model of yoga leggings with a seamless partition structure is constructed, and the clothing is designed with partition structure according to elastic requirements. From large to small, they are: waist, front of thigh; abdomen, outside of hip, back of thigh, knee, back of calf; buttocks; inner leg, reverse side of knee circumference; front side of calf. It provides a reference basis for the functional partition design of seamless yoga leggings.