JP7737876B2 - Innerwear - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act Application of Article 30, Paragraph 2 of the Patent Act was announced at the Gunze Spring/Summer 2022 General Exhibition held at Namba Midosuji Hall from September 8th to 10th, 2021, and at Nihonbashi Plaza Building from September 15th to 17th, 2021.

The present invention relates to innerwear worn in daily life by middle-aged and elderly people with reduced muscle strength and joint function to support walking and reduce fatigue. More specifically, the innerwear is comprised of a stretchable main fabric and multiple tightening sections with a higher stretch recovery rate than the main fabric, and covers the wearer from at least the waist to the ankles.

Patent Document 1 proposes tights suitable for training such as running, which have the function of increasing the range of motion of hip joint flexion by applying an assist force in the direction of hip joint flexion during running or walking.

These tights are made from a material with stretch recovery, and have areas that fit snugly against the body, covering the abdomen, buttocks, hip joints, and legs up to at least the top of the kneecap. A material with greater stretch recovery than the material of the back body is placed in the area of the rectus femoris muscle of the thigh from the front of the opening of the front body toward the kneecap, and for a length that reaches at least the top of the kneecap. This material with greater stretch recovery stretches when the hip joint is extended, and when the hip joint is flexed, the stretched material with greater stretch recovery contracts, assisting hip joint flexion.

WO2013-179440 publication

The conventional sports tights mentioned above use a material with greater stretch recovery than the material in the back, positioned from the front of the opening to the top of the kneecap in the front body, to promote hip flexion and increase stride length, thereby correcting form and improving performance.

However, when these sports tights are worn by middle-aged or elderly people with reduced muscle strength and joint function, the aforementioned assistive force can actually become a burden, making them more likely to tire.

Furthermore, in the case of tights such as those disclosed in Patent Document 1, in which a material with greater stretch recovery than the material of the back body is placed continuously from the opening of the front body, past the kneecap, to the ankle, a bending structure is adopted in which the lower leg is tilted backward from the long axis of the thigh to make it easier to bend the knee joint backward. As a result, even in an extended state without bending the knee, a force acts in the direction of tilting the lower leg backward, and for middle-aged and elderly people with reduced muscle strength and joint function, simply wearing them puts a heavy burden on the legs.

In view of the above-mentioned problems, the object of the present invention is to provide innerwear that can be worn in daily life by middle-aged and elderly people with reduced muscle strength and joint function, helping them maintain balance when walking and assisting with flexion and extension of the hip and knee joints, thereby reducing fatigue.

In order to achieve the above-mentioned object, a first characteristic configuration of innerwear according to the present invention is innerwear that is configured with a main fabric that exhibits stretchability and a plurality of tightening portions that have a greater stretch recovery rate than the main fabric, and that covers at least the wearer from the waist to the ankles, and the tightening portions are arranged on the left and right front body parts, and comprise strip-shaped thigh tightening portions that extend from a position above the greater trochanter to above the patella when worn, strip-shaped front crus tightening portions that extend from below the patella to the ankles when worn, and a band-shaped anterior crus tightening portion that extends ... and a posterior crus tightening portion comprising a band-shaped medial calf tightening portion that covers at least a portion of the lateral gastrocnemius muscle and extends down to the ankle, and a band-shaped lateral calf tightening portion that covers at least a portion of the lateral gastrocnemius muscle and extends down to the ankle, and when worn, the region corresponding to the kneecap is provided with a circular kneecap that has a smaller stretch recovery rate than the tightening portion, and a circular patella tightening portion that has a larger stretch recovery rate than the kneecap is provided around the kneecap, and the tightening portions help maintain balance when walking and assist the flexion or extension movements of the hip and knee joints.

The multiple tightening parts, which have a greater stretch recovery rate than the main fabric, assist movement around the wearer's hip and knee joints. In particular, by arranging the thigh tightening parts so that they extend from a position above the greater trochanter to above the patella, the assist force for hip flexion and other movements is appropriately adjusted so that even middle-aged and elderly people with reduced muscle strength and joint function are not placed under excessive strain when wearing the garment, making it easy to put on and take off on a daily basis. Furthermore, the inclusion of front and rear lower leg tightening parts assists flexion and extension movements around the knee joint, allowing good balance to be maintained when walking.
Furthermore, the patella tightening portion arranged around the circular kneecap tightens the area around the patella, preventing the innerwear from slipping at the knee and providing good support for the knee joint when walking, thereby increasing stability when walking.

The second characteristic feature of this garment is that, in addition to the first characteristic feature described above, the stretch rate of the body fabric, including at least the thigh tightening portions that cover the wearer's thighs, is greater than the stretch rate of the body fabric itself.

The stretch rate of the main fabric, including at least the thigh tightening portions that cover the wearer's thighs, is greater than the stretch rate of the main fabric. This means that while it exerts a tightening force when the hip joint is flexed, it stretches more easily than the main fabric when the hip joint is extended, allowing the assist force to be adjusted appropriately without interfering with hip joint movement.

The third characteristic configuration is, in addition to the first characteristic configuration described above, that it is equipped with a knee tightening portion that extends from the outer edge of the patella tightening portion to the popliteal fossa and has a greater extension recovery rate than the kneecap but a smaller extension recovery rate than the patella tightening portion.

The knee tightening section supports the muscles around the knee joint, stabilizing the balance of the lower limbs when walking.

The fourth characteristic feature of the present invention is that, in addition to the third characteristic feature described above, the front crus tightening portion is connected to the knee tightening portion or the patella tightening portion.

By connecting the front crus tightening section to the knee tightening section or patella tightening section, the tightening effect of the front crus tightening section is increased, making walking more stable.

The fifth characteristic configuration is that, in addition to any of the first to fourth characteristic configurations described above, when worn, the front crus tightening portion extends to the tarsal bones and is equipped with a metatarsal bone fixing portion that wraps around the foot in a band-like manner to include part of the metatarsal bones, and the front crus tightening portion is connected to the metatarsal bone fixing portion.

By extending the anterior lower leg tightening section to the tarsal bones and connecting it to the metatarsal fixation section, the ankle and ankle joint are properly supported, resulting in stable walking.

The sixth characteristic configuration is that, in addition to any one of the first to fifth characteristic configurations described above, the body fabric, the thigh tightening portions, the front crus tightening portions, and the rear crus tightening portions are made of weft knitted fabrics.

When the body fabric and the tightening sections, including the thigh tightening section, front crus tightening section, and rear crus tightening section, are made of stretchy weft knit fabric, the garment is easy to put on and take off, provides an excellent wearing comfort, reduces the strain on everyday walking movements, and allows for good walking balance.

The seventh characteristic feature of the present invention is that, in addition to any one of the first to sixth characteristic features described above, a gusset fabric separate from the body fabric is joined to the crotch of a pair of left and right legs.

The gusseted fabric reduces stress on the hip joints, reducing the strain on walking movements.

As explained above, the present invention provides innerwear that can be worn in daily life by middle-aged and elderly people with reduced muscle strength and joint function to maintain balance when walking, assist with flexion and extension of the hip and knee joints, and reduce fatigue.

(a) is an explanatory diagram of the innerwear according to the present invention as seen from the front, (b) is an explanatory diagram of the same as seen from the back, (c) is an explanatory diagram of the same as seen from the side, and (d) is an explanatory diagram of the magnitude of the elongation recovery rate of the tightening parts shown in the explanatory diagrams shown in (a) to (c). Illustrative diagram of elongation recovery rate and elongation rate 1(a) is an explanatory diagram showing the positions of the tightening parts of the innerwear corresponding to the wearer's skeleton, and FIG. 1(b) is an explanatory diagram of the foot bones as seen from the dorsum of the foot. FIG. 10 is a front view of the innerwear according to another embodiment.

An example of the innerwear according to the present invention will be described below with reference to the drawings.
1(a) to 1(c), the innerwear 1 is constructed using a weft knitted fabric, which is an example of a stretchable body fabric 2, so as to cover at least the wearer's waist to ankles, and includes a torso portion 1A with an opening 10 formed at the top, and left and right leg portions 1B, 1C extending below the torso portion 1A. In this embodiment, nylon yarn is used as the ground yarn that constitutes the weft knitted fabric. However, the type of ground yarn is not limited to nylon yarn, and polyester yarn or a blend of polyester yarn and cotton yarn can also be used.

The torso 1A is made up of a front and back body integrally formed from a cylindrically knitted circular fabric (weft knitted fabric). Below the torso 1A, the circular knitted fabric is cut lengthwise and the cut edges are sewn together to form the left and right leg sections 1B and 1C.

A separate gusset fabric 5 is attached to the crotch area of each pair of legs 1B, 1C. The presence of the gusset fabric 5 reduces stress on the hip joints, easing the strain on walking movements.

The opening 10 is made by knitting a predetermined number of polyurethane yarns in the wale direction onto nylon yarn, which is the ground yarn of the weft knit that makes up the body fabric 2, and then folding it back into a bag-like shape to form a band-like torso slip-prevention section 10A.

At the tip ends of the left and right leg sections 1B, 1C, openings 11 are formed on the back to expose the wearer's heels, and the tip ends 12 are cylindrically configured to cover the periphery of the feet.

The innerwear 1 described above includes a body fabric 2 that exhibits stretchability, as well as a plurality of tightening portions 3 that have a higher stretch recovery rate than the body fabric 2.
The tightening portions 3 include thigh tightening portions 3A, front crus tightening portions 3B, and rear crus tightening portions 3C, and the rear crus tightening portions 3C include medial sural tightening portions 3D and lateral sural tightening portions 3E.

The thigh tightening portions 3A are positioned on the left and right front body sections, and when worn, extend in a strip-like shape from a position above the greater trochanter 21 (see Figure 3(a)) below the torso anti-slip portion 10A to a position above the patella 22 (see Figure 3(a)).

When worn, the front crus tightening portion 3B extends in a band-like manner from below the patella 22 (see Figure 3(a)) to the ankle. The medial calf tightening portion 3D covers at least a portion of the medial gastrocnemius muscle when worn, and extends in a band-like manner to the ankle. The lateral calf tightening portion 3E covers at least a portion of the lateral gastrocnemius muscle when worn, and extends in a band-like manner to the ankle. In Figure 1(b), the lateral calf tightening portion 3E and the medial calf tightening portion 3D extend beyond the opening 11 in the heel and to the metatarsal tightening portion, but the lateral calf tightening portion 3E and the medial calf tightening portion 3D may also be configured to extend close to the opening 11.

In other words, the multiple tightening portions 3, which have a greater stretch recovery rate than the main fabric 2, assist movement around the wearer's hip and knee joints. In particular, by arranging the thigh tightening portion 3A so that it extends from a position above the greater trochanter 21 (see FIG. 3(a)) to above the patella 22 (see FIG. 3(a)), the assist force for hip flexion and other movements is appropriately adjusted so that even middle-aged and elderly people with reduced muscle strength and joint function are not placed under excessive strain when wearing the garment, making it easy to put on and take off on a daily basis. Furthermore, the provision of the front crus tightening portion 3B and rear crus tightening portion 3C assists flexion and extension movements around the knee joint, allowing good balance to be maintained when walking.

The stretch rate of the main fabric, including at least the thigh tightening portions 3A that cover the wearer's thighs, is set to a value greater than the stretch rate of the main fabric 2, allowing the assist force on the hip joints to be appropriately adjusted. It is preferable that the stretch rates of the other tightening portions 3 are also set to values greater than the stretch rate of the main fabric 2.

In this specification, as shown in Figure 2, the elongation recovery rate and elongation rate are defined as values measured using the following method in accordance with JIS L 1096:2010 L 8.16 E method (constant load method). The elongation recovery rate is also referred to as the elongation modulus.

The test specimens used to measure the stretch recovery rate were taken from the thigh tightening portion 3A for the high tightening portion, the knee tightening portion 3G for the medium tightening portion, and the body fabric 2 from the area covering the hamstrings, and the trunk slip prevention portion and metatarsal fixation portion were taken from a sample made of the same knitted structure. The test specimens were 20 mm wide x 200 mm long, with a test width of 20 mm, grip spacing of 100 mm, a constant load of 4.9 N, and a tensile speed of 200 mm/min. The test was repeated five times using a tensile tester (autograph), and the stretch recovery rate of the fabric after five cycles was calculated using the following formula.

The test specimens used to measure elongation were taken from the main fabric including the thigh tightening portion 3A for the high tightening portion, the knee tightening portion 3G for the medium tightening portion, and the main fabric 2 from the area covering the hamstrings, and the trunk slip prevention portion and metatarsal fixation portion were taken from a sample made of the same knitted structure. The size of the test specimen used to measure elongation was 100 mm wide x 200 mm long, with a test width of 100 mm and a grip spacing of 100 mm, and measurements were taken under the same conditions as for measuring the elongation recovery rate. The elongation rate of the fabric after five cycles was calculated using the following formula.

When fixing the test piece to the tensile tester (autograph) in measuring the stretch recovery rate and elongation rate, the test piece is fixed in a state where no tension is applied to the entire test piece (equivalent to a state where the test piece is placed) at a grip distance of 100 mm. When taking test pieces of the body fabric including the thigh tightening portions 3A, the test piece is taken so that the center line of the widthwise center of the thigh tightening portions 3A coincides with the center line of the widthwise direction of the test piece.
Elongation recovery rate (%) = {(L1-L2)/(L1-L0)}×100
Elongation rate = {(L1 - L0) / L0} x 100
In this specification, the elongation recovery rate (elastic modulus) is used as an index of the tightening force, and the larger the elongation recovery rate (elastic modulus), the stronger the tightening force.

As shown in Figure 3(a), the thigh tightening portion 3A extends below the opening 10, starting at a position approximately L10 = 2 cm above the greater trochanter 21 and ending at a position approximately L20 = 3 cm above the top of the patella 22. The distance L20 from the top of the patella 22 can be set appropriately to suit the expected body shape of the wearer. Increasing the distance L20 reduces the strain on the wearer's legs but also reduces support, while decreasing the distance L20 increases support but increases the strain on the wearer. The distance L20 is not limited to the values mentioned above, and is preferably set in the range of 2 to 10 cm, and more preferably in the range of 3 to 6 cm. L10 is preferably set in the range of 0.5 to 8 cm.

In this embodiment, the body fabric 2 is made of jersey knit, but the knitting structure is not particularly limited, and fabrics such as rib knit and smooth knit can also be used, and warp knit fabric can also be used in addition to weft knit fabric.

The tightening portions 3 can be knitted integrally with the knitted fabric that makes up the body fabric 2, and can be configured to obtain the desired tightening force by appropriately changing the type of knitting yarn, knitting density, knitting structure, and number of knitting yarns. This also applies to the other tightening portions 3 described below in addition to the above-mentioned tightening portions 3.

For example, the tightening portion 3 can be made of fabric made of a knitting structure including knit, miss knit, tuck knit, or a combination of these. The tightening portion 3 in this embodiment is knitted using knit and miss knit, but the knitting structures can be combined in consideration of the tightening force, elongation rate, etc. depending on the function required for each part. The strength of the tightening force can be adjusted by the arrangement of the knit, miss knit, and tuck knit, the number of times the arrangement is repeated, etc.

Alternatively, the tightening portion 3 may be formed by attaching a rubber material such as neoprene, or a PU panel, to the top of the body fabric 2. The tightening portion 3 may also be formed by applying a resin or other coating to the top surface of the body fabric 2.

The material of the fabric, including the body fabric 2 and the tightening portion 3, is not particularly limited and can be any material. As mentioned above, materials such as polyester, polyurethane, and polyester-cotton blends can be used.

The innerwear 1 described above further comprises a circular kneecap 4 in the region corresponding to the kneecap when worn, which has a smaller stretch recovery rate than the tightening portion 3, and a circular (annular) patella tightening portion 3F around the kneecap 4, which has a larger stretch recovery rate than the kneecap 4.

When not being worn, the kneecap 4 is formed into a vertically elongated oval shape with a major axis of 60 mm and a minor axis of 30 mm. It has the same knitting structure as the main fabric 2 and has a similar elongation recovery rate. Therefore, the kneecap 4 does not feel stiff when bending the knee joint, reducing the strain on the wearer's knees.

The patella tightening portion 3F is arranged in an elliptical ring shape 30 to 40 mm wide around the kneecap 4, and by tightening the area around the patella 22 (see Figure 3(a)), slippage at the knee is suppressed, the knee joint is well supported when walking, and a sense of stability is enhanced. The patella tightening portion 3F uses the same knitting structure as the thigh tightening portion 3A, and is set to have approximately the same stretch recovery rate as the thigh tightening portion 3A.

Furthermore, the innerwear 1 is equipped with a knee tightening portion 3G that extends from the outer edge of the patella tightening portion 3F to the popliteal fossa and has a greater stretch recovery rate than the kneecap 4 but a smaller stretch recovery rate than the patella tightening portion 3F.

The knee tightening portion 3G is preferably positioned in the area corresponding to the popliteal fossa, with a length of approximately 10 to 15 cm in the vertical direction, when not being worn. The knee tightening portion 3G supports the muscles around the knee, stabilizing the balance of the lower limbs when walking.

The front crus tightening portion 3B is positioned so that it connects to the knee tightening portion 3G, thereby increasing the effectiveness of the front crus tightening portion 3B and the rear crus tightening portion 3C and making walking more stable.

Furthermore, when the innerwear 1 is worn, the front crus tightening portion 3B extends to the tarsal bones 25 (see Figure 3(b)), and is equipped with a metatarsal fixing portion 6 that wraps around the foot in a band-like manner to include part of the metatarsal bones 26 (see Figure 3(b)), and the front crus tightening portion 3B is positioned so that it is connected to the metatarsal fixing portion 6. By extending the front crus tightening portion 3B to the tarsal bones 25 and connecting it to the metatarsal fixing portion 6, the ankle and area around the foot joint are properly supported, resulting in stable walking. Note that reference numeral 27 in Figure 3(b) denotes the phalanges.

As with the opening 10, a predetermined number of polyurethane threads may be knitted in the wale direction onto the nylon thread that forms the base thread of the body fabric 2 at the tip end 12, and folded back into a bag-like shape to form a band-like toe slip-prevention section 12A. In this case, the metatarsal support section 6 is realized by the toe slip-prevention section 12A.

As described above, the thigh tightening portions 3A, front crus tightening portions 3B, rear crus tightening portions 3C, patella tightening portions 3F, and knee tightening portions 3G are made of the same weft knit fabric as the main fabric 2. When the main fabric 2 and the tightening portions 3 including the thigh tightening portions 3A, front crus tightening portions 3B, and rear crus tightening portions 3C are made of stretchy weft knit fabric, the entire garment can be made thin, resulting in innerwear 1 that is easy to put on and take off and provides an excellent fit, reducing the strain on the wearer during everyday walking movements and allowing for good walking balance.

Furthermore, the innerwear 1 is equipped with an abdominal tightening portion 3I on the front body below the torso anti-slip portion 10A, and a buttocks tightening portion 3J on the back body.

In Figure 1 (d), the differences in the stretch recovery rate of the body fabric 2 and the tightening portions 3 are shown by the density of the hatching. The body fabric 2, which has the smallest stretch recovery rate, is shown by the unhatched rectangle on the left edge, and the thigh tightening portion 3A, front crus tightening portion 3B, rear crus tightening portion 3C, patella tightening portion 3F, and buttocks tightening portion 3J, which correspond to the high tightening portions where the stretch recovery rate is the greatest, are shown by the densely hatched rectangle on the right edge, and the knee tightening portion 3G and abdomen tightening portion 3I, which correspond to the medium tightening portions where the stretch recovery rate is an intermediate value, are shown by the sparsely hatched rectangle in the middle.

In this embodiment, the stretch recovery rate of the high tightening portion is set to 93.6%, the stretch recovery rate of the medium tightening portion is set to 83.8%, and the stretch recovery rate of the body fabric 2 is set to 80.8%, and it is preferable that the ratio of the stretch recovery rate of each tightening portion to the stretch recovery rate of the body fabric 2 is set in the range of 110-120% for the high tightening portion (117.0% in this embodiment) and in the range of 102-110% for the medium tightening portion (104.7% in this embodiment).

The stretch rate of the body fabric including the high tightening portions in the thighs is set to 66.3%, the stretch rate of the medium tightening portions is set to 56.8%, the stretch rate of the body fabric 2 is set to 61.6%, and the stretch rate of the torso anti-slip portions 10A and toe anti-slip portions 12A is set to 26.6%. It is preferable that the stretch rate of the body fabric including the high tightening portions in the thighs is greater than that of the body fabric 2, and that the stretch rates of the torso anti-slip portions 10A and toe anti-slip portions 12A are set to no more than half the stretch rate of the body fabric 2.

In the above-described embodiment, an example was described in which the thigh tightening portion 3A extends from a position above the greater trochanter to above the patella when worn, specifically, an embodiment in which the thigh tightening portion 3A extends below the shoe opening 10, starting at a position approximately L10 = 2 cm above the greater trochanter 21, and ending at a position approximately L20 = 3 cm above the top of the patella 22, but the extending position can be set appropriately in accordance with the stretch rate of the main fabric, including the thigh tightening portion 3A, in the thigh region. This embodiment is not particularly limited, but it is more effective if the stretch rate is smaller than that of the main fabric 2, for example.

However, as shown in Figure 4, even if the stretch recovery rate of the main fabric including the thigh tightening portion 3A in the thigh region is set to be greater than the stretch recovery rate of the main fabric 2, if the stretch rate of the thigh tightening portion 3A is equal to or greater than the stretch rate of the main fabric 2, a continuous band-like tightening portion may extend over the entire section from the waist anti-slip portion 10A or a position below the waist anti-slip portion 10A to the top of the patella.

If the stretch rate of the body fabric, including the thigh tightening portion 3A in the thigh area, is sufficiently high, the strain on the hip joints can be reduced, resulting in innerwear that not only provides adequate walking support but also feels great to wear.

The above describes examples of embodiments of the innerwear of the present invention, but the present invention is not limited to these descriptions, and the specific configuration, shape, materials, etc. of each part can be modified as appropriate within the scope of the effects of the present invention.

The innerwear of the present invention assists in the flexion and extension of the hip and knee joints while maintaining balance during walking, reducing fatigue and making it suitable for use in the daily lives of middle-aged and elderly people with reduced muscle strength and joint function.

1: Innerwear 1A: Torso 1B: Leg 1C: Leg 2: Body fabric 3: Tightening section 3A: Thigh tightening section 3B: Front crus tightening section 3C: Rear crus tightening section 3D: Medial calf tightening section 3E: Lateral calf tightening section 3F: Patella tightening section 3G: Knee tightening section 4: Kneecap 5: Gusset fabric 6: Metatarsal fixing section (toe slip prevention section)
10: Shoe opening 10A: Body slip prevention part 12A: Toe slip prevention part

Claims (7)

An innerwear comprising a body fabric that exhibits stretchability and a plurality of tightening portions that have a higher stretch recovery rate than the body fabric, and that covers at least the wearer from the waist to the ankles,
The tightening portion is
A belt-shaped thigh tightening portion is arranged on the left and right front body parts and extends from a position above the greater trochanter to above the patella when worn;
a belt-shaped front lower leg tightening portion that extends from below the patella to the ankle when worn;
a rear crus tightening portion that includes a band-shaped medial calf tightening portion that covers at least a portion of the medial gastrocnemius muscle and extends to the ankle when worn, and a band-shaped lateral calf tightening portion that covers at least a portion of the lateral gastrocnemius muscle and extends to the ankle;
Including,
In a worn state, the region corresponding to the kneecap is provided with a circular kneecap having a smaller elongation recovery rate than the tightening portion, and a circular patella tightening portion is provided around the kneecap having a larger elongation recovery rate than the kneecap,
The innerwear maintains walking balance and assists the flexion and extension of the hip and knee joints with the tightening portions. The innerwear of claim 1, characterized in that the stretch rate of the body fabric, including at least the thigh tightening portions that cover the wearer's thighs, is greater than the stretch rate of the body fabric. 2. The innerwear according to claim 1 , further comprising a knee tightening portion that extends from the outer edge of the patella tightening portion to the popliteal fossa and has a greater stretch recovery rate than the kneecap but a smaller stretch recovery rate than the patella tightening portion. 4. The innerwear according to claim 3 , wherein the front crus compressing portion is connected to the knee compressing portion or the patella compressing portion. The innerwear according to any one of claims 1 to 4, characterized in that when worn, the front crus tightening portion extends to the tarsal bones, includes a portion of the metatarsal bones, and is provided with a metatarsal bone fixing portion that wraps around in a band-like manner, and the front crus tightening portion is connected to the metatarsal bone fixing portion. 6. The innerwear according to any one of claims 1 to 5 , wherein the body fabric, the thigh tightening portions, the front crus tightening portions, and the rear crus tightening portions are made of weft knitted fabrics. 7. The innerwear according to claim 1, wherein a gusset fabric separate from the body fabric is joined to the crotch of each of the pair of left and right leg portions.