SHOES, DEVICES FOR SHOES, AND METHODS OF USING SHOES CROSS-REFERENCE TO RELATED PATENT APPLICATIONS [0001] This application claims priority from U.S. Provisional Patent App. Ser. No. 63/190,180, filed May 18, 2021, the entire contents of which are incorporated by reference herein. FIELD [0002] Embodiments of the present invention relate in general to footwear, and particularly to energy absorption and return systems for use in footwear. BACKGROUND [0003] In prior U.S. Patent No. 10,085,514, filed May 6, 2014, by Goldston et al., which issued on October 2, 2018, a discussion was provided of the desirability of providing for energy shock absorption and energy return by shoes. The entire contents of U.S. Patent No. 10,085,514 are incorporated by reference herein. SUMMARY OF THE DISCLOSURE [0004] A device in accordance with an embodiment for use in a shoe includes a first foot, a second foot, a third foot, and a fourth foot, and a first flexible leg, a second flexible leg, a third flexible leg, and a fourth flexible leg. The first flexible leg extends from the first foot and is curved. The second flexible leg extends from the second foot and is curved. The third flexible leg extends from the third foot and is curved. The fourth flexible leg extends from the fourth foot and is curved. In various embodiments, the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg are joined together with each other at a common area. The first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg are configured to store energy when a force is applied to the common area, and are configured to return energy when the force is removed from the common area. [0005] In various embodiments, the first foot, the second foot, the third foot, the fourth foot, the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg are formed as a single unit. In some embodiments, the single unit is formed of carbon fiber. In some embodiments, the single unit is formed of one or more of carbon fiber, poly-paraphenylene terephthalamide (known as Kevlar®), styrene, and/or a thermoplastic elastomer such as a polyether block amide (PEBA) material known as Pebax® that is manufactured by ARKEMA. In various embodiments, the common area is at a central location with respect to locations of the first foot, the second foot, the third foot, and the fourth foot. In various embodiments, the common area is raised in height as compared to a corresponding top surface of each of the first foot, the second foot, the third foot, and the fourth foot. In some embodiments, the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg each comprise one or more of carbon fiber, poly-paraphenylene terephthalamide (known as Kevlar®), styrene, and/or a thermoplastic elastomer such as a polyether block amide (PEBA) material known as Pebax®, or other suitable material. In various embodiments, the device is at least partially located in an opening in a midsole of a shoe. [0006] In various embodiments, the device further includes a spring extending from a bottom surface of the common area. In some embodiments, the device further includes a first spring extending from a bottom surface of the first foot, a second spring extending from a bottom surface of the second foot, a third spring extending from a bottom surface of the third foot, and a fourth spring extending from a bottom surface of the fourth foot. In further embodiments, the device includes a fifth spring extending from a bottom surface of the common area. In various embodiments, the first flexible leg and the third flexible leg together form a first arch. In various embodiments, the second flexible leg and the fourth flexible leg together form a second arch. In some embodiments, a center of the first arch and a center of the second arch are joined together at the common area. [0007] A shoe in accordance with an embodiment includes a midsole and a device located at least partially in an opening in the midsole. In various embodiments, the device includes a first foot, a second foot, a third foot, and a fourth foot, a first flexible leg that extends from the first foot and is curved, a second flexible leg that extends from the second foot and is curved, a third flexible leg that extends from the third foot and is curved, and a fourth flexible leg that extends from the fourth foot and is curved. In various embodiments, the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg are joined together with each other at a common area. [0008] A method of using a device in a shoe in accordance with an embodiment includes applying force to a common area at which a first flexible leg, a second flexible leg, a third flexible leg, and a fourth flexible leg of the device are joined together to cause a first spring located under a first foot connected to the first flexible leg to compress, and to cause a second spring located under a second foot connected to the second flexible leg to compress, and to cause a third spring located under a third foot connected to the third flexible leg to compress, and to cause a fourth spring located under a fourth foot connected to the fourth flexible leg to compress, and to cause a fifth spring located under the common area to compress, and to cause the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg to flex to a flexed position, so as to store potential energy. In various embodiments, the method further includes releasing the force from the common area to allow the first spring, the second spring, the third spring, the fourth spring, and the fifth spring to stretch, and to allow the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg to return back from the flexed position, so as to return energy. [0009] A device in accordance with another embodiment for use in a shoe includes a first foot, a second foot, a third foot, and a fourth foot, and a first flexible leg, a second flexible leg, a third flexible leg, and a fourth flexible leg. The first flexible leg extends from the first foot and is curved. The second flexible leg extends from the second foot and is curved. The third flexible leg extends from the third foot and is curved. The fourth flexible leg extends from the fourth foot and is curved. The first flexible leg and the third flexible leg are joined together with each other as a single unit to form a first arch from the first foot to the third foot. The second flexible leg and the fourth flexible leg are joined together with each other as a single unit to form a second arch from the second foot to the fourth foot. The second arch has a center portion that is located under a center portion of the first arch. [0010] In various embodiment, the device further includes a spring extending from a bottom surface of the center portion of the second arch. In various embodiments, the device further includes a first spring extending from a bottom surface of the first foot, a second spring extending from a bottom surface of the second foot, a third spring extending from a bottom surface of the third foot, and a fourth spring extending from a bottom surface of the fourth foot. In some embodiments, the device further includes a fifth spring extending from a bottom surface of the center portion of the second arch. [0011] A shoe in accordance with another embodiment includes a midsole and a device located at least partially in an opening in the midsole. The device includes a first foot, a second foot, a third foot, and a fourth foot, and a first flexible leg, a second flexible leg, a third flexible leg, and a fourth flexible leg. The first flexible leg extends from the first foot and is curved. The second flexible leg extends from the second foot and is curved. The third flexible leg extends from the third foot and is curved. The fourth flexible leg extends from the fourth foot and is curved. The first flexible leg and the third flexible leg are joined together with each other to form a first arch from the first foot to the third foot. The second flexible leg and the fourth flexible leg are joined together with each other to form a second arch from the second foot to the fourth foot. The second arch has a center portion that is located under a center portion of the first arch. In various embodiments, the device further includes a first spring extending from a bottom surface of the first foot, a second spring extending from a bottom surface of the second foot, a third spring extending from a bottom surface of the third foot, a fourth spring extending from a bottom surface of the fourth foot, and a fifth spring extending from a bottom surface of the center portion of the second arch. [0012] A method in accordance with an embodiment of using the device in a shoe includes applying force to the center portion of the first arch to cause force to be applied to the center portion of the second arch, and to cause the first spring located under the first foot connected to the first flexible leg to compress, and to cause the second spring located under the second foot connected to the second flexible leg to compress, and to cause the third spring located under the third foot connected to the third flexible leg to compress, and to cause the fourth spring located under the fourth foot connected to the fourth flexible leg to compress, and to cause the fifth spring located under the center portion of the second arch to compress, and to cause the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg to flex to a flexed position, so as to store potential energy. In various embodiments, the method further includes releasing the force from the center portion of the first arch to allow the first spring, the second spring, the third spring, the fourth spring, and the fifth spring to stretch, and to allow the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg to return back from the flexed position, so as to return energy. In various embodiments, the center portion of the second arch is located below the center portion of the first arch. BRIEF DESCRIPTION OF THE DRAWINGS [0013] FIG. 1 shows a shoe in accordance with an embodiment. [0014] FIG. 2 shows an exploded view of a shoe including a device in accordance with an embodiment. [0015] FIG. 3A shows the device from FIG. 2 for use in a shoe in accordance with an embodiment. [0016] FIG. 3B shows another embodiment of a device that includes a center spring for use in a shoe. [0017] FIG. 3C shows another embodiment of a device that includes four side springs for use in a shoe. [0018] FIG. 3D shows another embodiment of a device that includes a center spring and four side springs for use in a shoe. [0019] FIG. 4A shows another embodiment of a device for use in a shoe. [0020] FIG. 4B shows another embodiment of a device that includes a center spring for use in a shoe. [0021] FIG. 4C shows another embodiment of a device that includes four side springs for use in a shoe. [0022] FIG. 4D shows another embodiment of a device that includes a center spring and four side springs for use in a shoe. [0023] FIGS. 5A, 5B, and 5C show example states of the device of FIG. 4B, where FIG. 5A shows an uncompressed state, FIG. 5B shows a state when the device is under pressure, and FIG. 5C shows a state when the device has bounced back. [0024] FIG. 6 shows a portion of an embodiment of a shoe illustrating exemplary locations at which one or more devices in accordance with any of the embodiments may be located. [0025] FIG. 7 is a flowchart of a method in accordance with an embodiment. [0026] FIG. 8 is a flowchart of a method in accordance with an embodiment. DETAILED DESCRIPTION [0027] FIG. 1 shows a shoe 100 in accordance with an embodiment. The shoe 100 includes an outsole 202, a midsole 203, an upper 204, and a fastening member 205. The shoe 100 has various portions, including a forefoot portion 101, a ball portion 102, an arch portion 103, and a heel portion 104. The outsole 202 is designed to be placed on the ground in normal operation of the shoe 100. The upper 204 includes an opening for a foot of a user and means for tightening the shoe 100 around the foot of the user, such as the fastening member 205, which may be, for example, laces, a zipper, or the like. [0028] The forefoot portion 101 of the shoe 100 is located at the front of the shoe 100, and the forefoot portion 101 may support the toes of a foot of a human when the foot of the human is inserted into the shoe 100. The ball portion 102 is located adjacent to the forefoot portion 101, and the ball portion 102 may support the ball of a foot of a human when the foot of the human is inserted into the shoe 100. The arch portion 103 is located adjacent to the ball portion 102, and may provide support to an arch of a foot of a human when the foot of the human is inserted into the shoe 100. The heel portion 104 is located adjacent to the arch portion 103 and at the rear of the shoe 100, and may provide support to a heel of a foot of a human when the foot of the human is inserted into the shoe 100. [0029] FIG. 2 shows an exploded view of the shoe 100 in accordance with an embodiment. The shoe 100 includes the outsole 202, the midsole 203, an insole 216, and a device 231. In various embodiments, the shoe further includes a plate 222. The insole 216 is located above the plate 222. There is a cavity or opening 217 in the midsole 203 into which at least a portion of the device 231 is insertable. For example, the device 231 may be positioned within the opening 217 in the midsole 203 such that bottom surfaces of the device 231 contact a top surface of the outsole 202. In some embodiments, the opening 217 is a partial opening in the midsole 203 forming a cavity in which the device 231 may be positioned such that bottom surfaces of the device 231 contact a surface of the midsole 203 within the cavity. Though not shown in FIG. 2, the shoe 100 can have other elements such as the upper 204 and the fastening member 205 as shown in FIG. 1. Referring to FIGS. 1 and 2, the shoe 100 also has the forefoot portion 101, ball portion 102, arch portion 103, and heel portion 104 in a longitudinal direction. [0030] In various embodiments, the plate 222 is a carbon fiber plate. Also, in various embodiments, the plate 222 has a same or similar shape as the insole 216 in length and width directions. In some embodiments, the plate 222 has a shorter length than the insole 216. In various embodiments, the plate 222 extends across substantially an entire length of the shoe 100. For example, in some embodiments, the plate 222 extends within an area bounded by a wall of the midsole 203 at the back of the shoe 100 to a wall of the midsole 203 at the front of the shoe 100. In various embodiments, the plate 222 extends from the heel portion 104 of the shoe 100 and through the arch portion 103 and the ball portion 102 of the shoe 100 and into the forefoot portion 101 of the shoe 100. In some embodiments, there is a sockliner positioned above the insole 216 that is on an opposite side of the insole 216 from the plate 222. In various embodiments, the insole 216 comprises an ethylene- vinyl acetate (EVA) material, or the like. In various embodiments, the midsole 203 comprises a thermoplastic elastomer such as a polyether block amide (PEBA) material, such as the PEBA material known as Pebax® that is manufactured by ARKEMA. In some embodiments, a Shore type A durometer value of the midsole 203 is less than 40. In some embodiments, a Shore type A durometer value of the midsole 203 is greater than 40. [0031] In various embodiments, the device 231 is an energy storage and return device that acts as a trampoline to store potential energy when compressed by a foot of a human wearing the shoe 100, and then to return energy to the foot of the human as the foot of the human is lifted. In various embodiments, a rear end of the device 231 is positioned near a half-way point of a length of the shoe 100 and the device 231 extends all the way to near a front of the shoe 100 where it would be under the toes of a user of the shoe 100. In various embodiments, the device 231 extends from a position in the arch portion 103 of the shoe 100 and through the ball portion 102 of the shoe 100 and into the forefoot portion 101 of the shoe 100 to near a front of the forefoot portion 101 of the shoe 100. In some embodiments, the device 231 is positioned entirely within the forefoot portion 101 of the shoe 100. In some embodiment, the device 231 is positioned entirely within the ball portion 102 of the shoe 100. In some embodiments, the device 231 is positioned entirely within the heel portion 104 of the shoe 100. Other positions of the device 231 within the shoe 100 are also possible. [0032] In various embodiments, the plate 222 is glued or otherwise affixed to the device 231. For example, a top surface of the device 231 in various embodiments is glued to a bottom surface of the plate 222 during manufacture. In various embodiments, the plate 222 is affixed, such as being permanently affixed, to the device 231 such that the plate 222 works together with the device 231 to provide energy return to a user using the shoe 100. In various embodiments, the plate 222 is affixed to the device 231 such that an energy return of the plate 222 works with a kinetic release of the device 231 when a user is using the shoe 100. In some embodiments, the plate 222 is omitted from the shoe 100, and the device 231 has an upper surface in contact with a bottom surface of the insole 216. [0033] FIG. 3A shows the device 231 from FIG. 2 for use in a shoe in accordance with an embodiment. The device 231 includes an energy storage and return structure 240. The energy storage and return structure 240 includes a first foot 261, a second foot 262, a third foot 263, and a fourth foot 264, and a first flexible leg 251, a second flexible leg 252, a third flexible leg 253, and a fourth flexible leg 254. The first flexible leg 251 extends from the first foot 261 and is curved. The second flexible leg 252 extends from the second foot 262 and is curved. The third flexible leg 253 extends from the third foot 263 and is curved. The fourth flexible leg 254 extends from the fourth foot 264 and is curved. The first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 are joined together with each other at a common area 380. In various embodiments, the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 are joined together with each other at the common area 380 by being manufactured as a single unit. The first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 are configured to store energy when a force is applied to the common area 380, and are configured to return energy when the force is removed from the common area 380. [0034] In various embodiments, the first foot 261, the second foot 262, the third foot 263, the fourth foot 264, the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 are formed as a single unit. In some embodiments, such a single unit is formed of carbon fiber. In some embodiments, such a single unit is formed of one or more of carbon fiber, rubber, poly-paraphenylene terephthalamide (known as Kevlar®), styrene, and/or a thermoplastic elastomer such as a polyether block amide (PEBA) material known as Pebax®. In various embodiments, the energy storage and return structure 240 is formed of one or more of carbon fiber, rubber, poly-paraphenylene terephthalamide (known as Kevlar®), styrene, and/or a thermoplastic elastomer such as a polyether block amide (PEBA) material known as Pebax®, or other material that allows for flexing and returning from a flexed state. In various embodiments, the common area 380 is at a central location with respect to locations of the first foot 261, the second foot 262, the third foot 263, and the fourth foot 264. In various embodiments, the common area 380 is raised in height as compared to a corresponding top surface of each of the first foot 261, the second foot 262, the third foot 263, and the fourth foot 264. In some embodiments, the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 each comprise one or more of carbon fiber, rubber, poly-paraphenylene terephthalamide (known as Kevlar®), styrene, and/or a thermoplastic elastomer such as a polyether block amide (PEBA) material known as Pebax®. In various embodiments, the device 231 is at least partially located in an opening in a midsole of a shoe. [0035] In various embodiments, the first flexible leg 251 and the third flexible leg 253 together form a first arch 255 from the first foot 261 to the third foot 263. In various embodiments, the second flexible leg 252 and the fourth flexible leg 254 together form a second arch 256 from the second foot 262 to the fourth foot 264. In some embodiments, a center of the first arch 255 and a center of the second arch 256 are joined together as part of a single unit at the common area 380 and are angled with respect to each other. [0036] The first flexible leg 251 has a top surface 301 and a bottom surface 302. The second flexible leg 252 has a top surface 321 and a bottom surface 322. The third flexible leg 253 has a top surface 341 and a bottom surface 342. The fourth flexible leg 254 has a top surface 361 and a bottom surface 362. The first foot 261 has a top surface 311 and a bottom surface 312. The second foot 262 has a top surface 331 and a bottom surface 332. The third foot 263 has a top surface 351 and a bottom surface 352. The fourth foot 264 has a top surface 371 and a bottom surface 372. The common area 380 has a top surface 381 and a bottom surface 382. [0037] With reference to FIGS. 2 and 3A, in various embodiments, the device 231 is located at least partially within the opening 217 in the midsole 203 of the shoe 100 such that the bottom surface 312 of the first foot 261, the bottom surface 332 of the second foot 262, the bottom surface 352 of the third foot 263, and the bottom surface 372 of the fourth foot 264 are flat on a top surface of the outsole 202. In various embodiments, the device 231 is located entirely within the opening 217 in the midsole 203 of the shoe 100. In various embodiments, a first portion of a bottom surface of the plate 222 is glued to the top surface 381 of the common area 380 of the device 231, and a second portion of the bottom surface of the plate 222 lays on a surface of the midsole 203 of the shoe 100. Also, in various embodiments, the insole 216 lays on a top surface of the plate 222. [0038] A method of using the device 231 in the shoe 100 in accordance with an embodiment includes applying force, such as from a foot of a human user, to the common area 380 at which the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 of the device 231 are joined together to cause the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 to flex to a flexed position, so as to store potential energy. In various embodiments, the method further includes releasing the force from the common area 380, such as by lifting the foot of the human user, to allow the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 to return back from the flexed position, so as to return energy to the foot of the human user. In various embodiments, the force is applied to the common area 380 from the foot of the human user by the foot of the human user pressing on the insole 216 to cause the plate 222 to apply the force to the common area 380. [0039] FIG. 3B shows a device 232 in accordance with another embodiment. With reference to FIGS. 3A and 3B, the device 232 is similar to the device 231 and includes the energy storage and return structure 240 of the device 231, but the device 232 also includes a center spring 395 that is positioned on the bottom surface 382 of the common area 380. The label numbers in FIG. 3B that are the same as label numbers in FIG. 3A denote the same structures. In various embodiments, the spring 395 is a coil spring. In various other embodiments, the spring 395 is a wave spring or other type of spring. The spring 395 provides for additional energy storage and return when the device 232 is used in a shoe. [0040] With reference to FIGS. 2 and 3B, the device 232 can be used in place of the device 231 in the shoe 100. In some embodiments, a bottom of the spring 395 would be in contact with a top surface of the outsole 202 when the device 232 is positioned at least partially within the opening 217 in the midsole 203 of the shoe 100. Also, in various embodiments, the bottom surface 312 of the first foot 261, the bottom surface 332 of the second foot 262, the bottom surface 352 of the third foot 263, and the bottom surface 372 of the fourth foot 264 are flat on a top surface of the outsole 202 when the device 232 is positioned at least partially within the opening 217 in the midsole 203 of the shoe 100. In various embodiments, the device 232 is located entirely within the opening 217 in the midsole 203 of the shoe 100. In various embodiments, a first portion of a bottom surface of the plate 222 is glued to the top surface 381 of the common area 380 of the device 232, and a second portion of the bottom surface of the plate 222 lays on a surface of the midsole 203 of the shoe 100. Also, in various embodiments, the insole 216 lays on a top surface of the plate 222. [0041] A method of using the device 232 in the shoe 100 in accordance with an embodiment includes applying force, such as from a foot of a human user, to the common area 380 at which the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 of the device 232 are joined together to cause the center spring 395 to compress, and to cause the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 to flex to a flexed position, so as to store potential energy. In various embodiments, the method further includes releasing the force from the common area 380, such as by lifting the foot of the human user, to allow the center spring 395 to expand from the compressed state and to allow the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 to return back from the flexed position, so as to return energy to the foot of the human user. In various embodiments, the force is applied to the common area 380 from the foot of the human user by the foot of the human user pressing on the insole 216 to cause the plate 222 to apply the force to the common area 380. [0042] FIG. 3C shows a device 233 in accordance with another embodiment. With reference to FIGS. 3A and 3C, the device 233 is similar to the device 231 and includes the energy storage and return structure 240 of the device 231, but the device 233 further includes a first spring 391 extending from the bottom surface 312 of the first foot 261, a second spring 392 extending from the bottom surface 332 of the second foot 262, a third spring 393 extending from the bottom surface 352 of the third foot 263, and a fourth spring 394 extending from the bottom surface 372 of the fourth foot 264. The label numbers in FIG. 3C that are the same as label numbers in FIG. 3A denote the same structures. In various embodiments, the first spring 391, the second spring 392, the third spring 393, and the fourth spring 394 are coil springs. In various other embodiments, the first spring 391, the second spring 392, the third spring 393, and the fourth spring 394 are wave springs or other types of springs. The first spring 391, the second spring 392, the third spring 393, and the fourth spring 394 provide for additional energy storage and return when the device 233 is used in a shoe. [0043] With reference to FIGS. 2 and 3C, the device 233 can be used in place of the device 231 in the shoe 100. In some embodiments, a corresponding bottom of each of the first spring 391, the second spring 392, the third spring 393, and the fourth spring 394 would be in contact with a top surface of the outsole 202 when the device 233 is positioned at least partially within the opening 217 in the midsole 203 of the shoe 100. In various embodiments, the device 233 is located entirely within the opening 217 in the midsole 203 of the shoe 100. In various embodiments, a first portion of a bottom surface of the plate 222 is glued to the top surface 381 of the common area 380 of the device 233, and a second portion of the bottom surface of the plate 222 lays on a surface of the midsole 203 of the shoe 100. Also, in various embodiments, the insole 216 lays on a top surface of the plate 222. [0044] A method of using the device 233 in the shoe 100 in accordance with an embodiment includes applying force, such as from a foot of a human user, to the common area 380 at which the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 of the device 233 are joined together to cause the first spring 391, the second spring 392, the third spring 393, and the fourth spring 394 to compress, and to cause the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 to flex to a flexed position, so as to store potential energy. In various embodiments, the method further includes releasing the force from the common area 380, such as by lifting the foot of the human user, to allow the first spring 391, the second spring 392, the third spring 393, and the fourth spring 394 to expand from the compressed state and to allow the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 to return back from the flexed position, so as to return energy to the foot of the human user. In various embodiments, the force is applied to the common area 380 from the foot of the human user by the foot of the human user pressing on the insole 216 to cause the plate 222 to apply the force to the common area 380. [0045] FIG. 3D shows a device 234 in accordance with another embodiment. With reference to FIGS. 3A and 3D, the device 234 is similar to the device 231 and includes the energy storage and return structure 240 of the device 231, but the device 234 further includes the first spring 391 extending from the bottom surface 312 of the first foot 261, the second spring 392 extending from the bottom surface 332 of the second foot 262, the third spring 393 extending from the bottom surface 352 of the third foot 263, the fourth spring 394 extending from the bottom surface 372 of the fourth foot 264, and the center spring 395 that is a fifth spring extending from the bottom surface 382 of the common area 380. The label numbers in FIG. 3D that are the same as label numbers in FIG. 3A denote the same structures. In various embodiments, the first spring 391, the second spring 392, the third spring 393, the fourth spring 394, and the center spring 395 are coil springs. In various other embodiments, the first spring 391, the second spring 392, the third spring 393, the fourth spring 394, and the center spring 395 are wave springs or other types of springs. The first spring 391, the second spring 392, the third spring 393, the fourth spring 394, and the center spring 395 provide for additional energy storage and return when the device 234 is used in a shoe [0046] With reference to FIGS. 2 and 3D, the device 234 can be used in place of the device 231 in the shoe 100. In some embodiments, a corresponding bottom of each of the first spring 391, the second spring 392, the third spring 393, the fourth spring 394, and the center spring 395 would be in contact with a top surface of the outsole 202 when the device 234 is positioned at least partially within the opening 217 in the midsole 203 of the shoe 100. In various embodiments, the device 234 is located entirely within the opening 217 in the midsole 203 of the shoe 100. In various embodiments, a first portion of a bottom surface of the plate 222 is glued to the top surface 381 of the common area 380 of the device 234, and a second portion of the bottom surface of the plate 222 lays on a surface of the midsole 203 of the shoe 100. Also, in various embodiments, the insole 216 lays on a top surface of the plate 222. [0047] A method of using the device 234 in the shoe 100 in accordance with an embodiment includes applying force, such as from a foot of a human user, to the common area 380 at which the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 of the device 234 are joined together to cause the first spring 391, the second spring 392, the third spring 393, the fourth spring 394, and the center spring 395 to compress, and to cause the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 to flex to a flexed position, so as to store potential energy. In various embodiments, the method further includes releasing the force from the common area 380, such as by lifting the foot of the human user, to allow the first spring 391, the second spring 392, the third spring 393, the fourth spring 394, and the center spring 395 to expand from the compressed state and to allow the first flexible leg 251, the second flexible leg 252, the third flexible leg 253, and the fourth flexible leg 254 to return back from the flexed position, so as to return energy to the foot of the human user. In various embodiments, the force is applied to the common area 380 from the foot of the human user by the foot of the human user pressing on the insole 216 to cause the plate 222 to apply the force to the common area 380. [0048] FIG. 4A shows a device 431 in accordance with another embodiment for use in a shoe. The device 431 includes an energy storage and return structure 440. The energy storage and return structure 440 includes a first foot 461, a second foot 462, a third foot 463, and a fourth foot 464, and a first flexible leg 451, a second flexible leg 452, a third flexible leg 453, and a fourth flexible leg 454. The first flexible leg 451 extends from the first foot 461 and is curved. The second flexible leg 452 extends from the second foot 462 and is curved. The third flexible leg 453 extends from the third foot 463 and is curved. The fourth flexible leg 454 extends from the fourth foot 464 and is curved. The first flexible leg 451 and the third flexible leg 453 are joined together with each other as a single unit to form a first arch 455 from the first foot 461 to the third foot 463. In various embodiments, the first flexible leg 451 and the third flexible leg 453 are joined together with each other by being manufactured as a single unit that is continuous as the first arch 455 from the first foot 461 to the third foot 463. The second flexible leg 452 and the fourth flexible leg 454 are joined together with each other as a single unit to form a second arch 456 from the second foot 462 to the fourth foot 464. In various embodiments, the second flexible leg 452 and the fourth flexible leg 454 are joined together with each other by being manufactured as a single unit that is continuous as the second arch 456 from the second foot 462 to the fourth foot 464. The second arch 456 has a center portion 583 that is located under a center portion 580 of the first arch 455. [0049] In various embodiments, the first foot 461, the second foot 462, the third foot 463, the fourth foot 464, the first flexible leg 451, the second flexible leg 452, the third flexible leg 453, and the fourth flexible leg 454 are formed of one or more of carbon fiber, poly- paraphenylene terephthalamide (known as Kevlar®), styrene, and/or a thermoplastic elastomer such as a polyether block amide (PEBA) material known as Pebax®. In various embodiments, the energy storage and return structure 440 is formed of one or more of carbon fiber, rubber, poly-paraphenylene terephthalamide (known as Kevlar®), styrene, and/or a thermoplastic elastomer such as a polyether block amide (PEBA) material known as Pebax®, or other material that allows for flexing and returning from a flexed state. In various embodiments, the center portion 580 of the first arch 455 is at a central location with respect to locations of the first foot 461, the second foot 462, the third foot 463, and the fourth foot 464. In various embodiments, the center portion 580 is raised in height as compared to a corresponding top surface of each of the first foot 461, the second foot 462, the third foot 463, and the fourth foot 464. In some embodiments, the first flexible leg 451, the second flexible leg 452, the third flexible leg 453, and the fourth flexible leg 454 each comprise one or more of carbon fiber, poly-paraphenylene terephthalamide (known as Kevlar®) styrene and/or a thermoplastic elastomer such as a polyether block amide ĨPEBA) material known as Pebax®. In various embodiments, the device 431 is at least partially located in an opening in a midsole of a shoe. [0050] The first flexible leg 451 has a top surface 501 and a bottom surface 502. The second flexible leg 452 has a top surface 521 and a bottom surface 522. The third flexible leg 453 has a top surface 541 and a bottom surface 542. The fourth flexible leg 454 has a top surface 561 and a bottom surface 562. The first foot 461 has a top surface 511 and a bottom surface 512. The second foot 462 has a top surface 531 and a bottom surface 532. The third foot 463 has a top surface 551 and a bottom surface 552. The fourth foot 464 has a top surface 571 and a bottom surface 572. The center portion 580 of the first arch 455 has a top surface 581 and a bottom surface 582. The center portion 583 of the second arch 456 has a top surface 584 and a bottom surface 585. [0051] With reference to FIGS. 2 and 4A, the device 431 can be used in place of the device 231 in the shoe 100. In various embodiments, the device 431 is located at least partially within the opening 217 in the midsole 203 of the shoe 100 such that the bottom surface 512 of the first foot 461, the bottom surface 532 of the second foot 462, the bottom surface 552 of the third foot 463, and the bottom surface 572 of the fourth foot 464 are flat on a top surface of the outsole 202. In various embodiments, a first portion of a bottom surface of the plate 222 is glued to the top surface 581, and a second portion of the bottom surface of the plate 222 lays on a surface of the midsole 203 of the shoe 100. Also, in various embodiments, the insole 216 lays on a top surface of the plate 222. [0052] A method of using the device 431 in the shoe 100 in accordance with an embodiment includes applying force to the center portion 580 of the first arch 455 to cause force to be applied to the center portion 583 of the second arch 456, so as to cause the first flexible leg 451, the second flexible leg 452, the third flexible leg 453, and the fourth flexible leg 454 to flex to a flexed position, so as to store potential energy. In various embodiments, the method further includes releasing the force from the center portion 580 of the first arch 455 to allow the first flexible leg 451, the second flexible leg 452, the third flexible leg 453, and the fourth flexible leg 454 to return back from the flexed position, so as to return energy. In various embodiments, the center portion 583 of the second arch 456 is located below the center portion 580 of the first arch 455. [0053] FIG. 4B shows a device 432 in accordance with another embodiment. With reference to FIGS. 4A and 4B, the device 432 is similar to the device 431 and includes the energy storage and return structure 440 of the device 431, but the device 432 further includes a spring 595 that is positioned on the bottom surface 585 of the center portion 583 of the second arch 456. The label numbers in FIG. 4B that are the same as label numbers in FIG. 4A denote the same structures. In various embodiments, the spring 595 is a coil spring. In various other embodiments, the spring 595 is a wave spring or other type of spring. The spring 595 provides for additional energy storage and return when the device 432 is used in a shoe. [0054] With reference to FIGS. 2 and 4B, the device 432 can be used in place of the device 231 in the shoe 100. In some embodiments, a bottom of the spring 595 would be in contact with a top surface of the outsole 202 when the device 432 is positioned at least partially within the opening 217 in the midsole 203 of the shoe 100. In various embodiments, the bottom surface 512 of the first foot 461, the bottom surface 532 of the second foot 462, the bottom surface 552 of the third foot 463, and the bottom surface 572 of the fourth foot 464 are flat on a top surface of the outsole 202. In various embodiments, a first portion of a bottom surface of the plate 222 is glued to the top surface 581, and a second portion of the bottom surface of the plate 222 lays on a surface of the midsole 203 of the shoe 100. Also, in various embodiments, the insole 216 lays on a top surface of the plate 222. [0055] A method of using the device 432 in the shoe 100 in accordance with an embodiment includes applying force to the center portion 580 to cause force to be applied to the center portion 583, so as to cause the first flexible leg 451, the second flexible leg 452, the third flexible leg 453, and the fourth flexible leg 454 to flex to a flexed position, and to compress the spring 595, so as to store potential energy. In various embodiments, the method further includes releasing the force from the center portion 580 to allow the first flexible leg 451, the second flexible leg 452, the third flexible leg 453, and the fourth flexible leg 454 to return back from the flexed position, and to allow the spring 595 to expand from the compressed state so as to return energy. [0056] FIGS. 5A, 5B, and 5C show stages of the device 432 during use. FIG. 5A shows the device 432 with the energy storage and return structure 440 and the spring 595 prior to a force being applied. FIG. 5B shows the device 432 with the energy storage and return structure 440 and the spring 595 when the force is applied to place the device 432 under pressure. FIG. 5C shows the device 432 with the energy storage and return structure 440 and the spring 595 when the force has been removed to allow the device 432 to bounce back and return energy. [0057] FIG. 4C shows a device 433 in accordance with another embodiment. With reference to FIGS. 4A and 4C, the device 433 is similar to the device 431 and includes the energy storage and return structure 440 of the device 431, but the device 433 further includes a first spring 591 extending from the bottom surface 512 of the first foot 461, a second spring 592 extending from the bottom surface 532 of the second foot 462, a third spring 593 extending from the bottom surface 552 of the third foot 463, and a fourth spring 594 extending from the bottom surface 572 of the fourth foot 464. The label numbers in FIG. 4C that are the same as label numbers in FIG. 4A denote the same structures. In various embodiments, the first spring 591, the second spring 592, the third spring 593, and the fourth spring 594 are coil springs. In various other embodiments, they are wave springs or other types of springs. The first spring 591, the second spring 592, the third spring 593, and the fourth spring 594 provide for additional energy storage and return when the device 433 is used in a shoe. [0058] With reference to FIGS. 2 and 4C, the device 433 can be used in place of the device 231 in the shoe 100. In some embodiments, a corresponding bottom of each of the first spring 591, the second spring 592, the third spring 593, and the fourth spring 594 would be in contact with a top surface of the outsole 202 when the device 433 is positioned at least partially within the opening 217 in the midsole 203 of the shoe 100. In various embodiments, a first portion of a bottom surface of the plate 222 is glued to the top surface 581, and a second portion of the bottom surface of the plate 222 lays on a surface of the midsole 203 of the shoe 100. Also, in various embodiments, the insole 216 lays on a top surface of the plate 222. [0059] A method of using the device 433 in the shoe 100 in accordance with an embodiment includes applying force to the center portion 580 to cause force to be applied to the center portion 583, so as to cause the first flexible leg 451, the second flexible leg 452, the third flexible leg 453, and the fourth flexible leg 454 to flex to a flexed position, and to compress the first spring 591, the second spring 592, the third spring 593, and the fourth spring 594, so as to store potential energy. In various embodiments, the method further includes releasing the force from the center portion 580 to allow the first flexible leg 451, the second flexible leg 452, the third flexible leg 453, and the fourth flexible leg 454 to return back from the flexed position, and to allow the first spring 591, the second spring 592, the third spring 593, and the fourth spring 594 to expand from the compressed state so as to return energy. [0060] FIG. 4D shows a device 434 in accordance with another embodiment. With reference to FIGS. 4A and 4D, the device 434 is similar to the device 431 and includes the energy storage and return structure 440 of the device 431, but the device 434 further includes the first spring 591 extending from the bottom surface 512 of the first foot 461, the second spring 592 extending from the bottom surface 532 of the second foot 462, the third spring 593 extending from the bottom surface 552 of the third foot 463, the fourth spring 594 extending from the bottom surface 572 of the fourth foot 464, and the spring 595 that is a fifth spring and that is positioned on the bottom surface 585 of the center portion 583 of the second arch 456. The label numbers in FIG. 4D that are the same as label numbers in FIG. 4A denote the same structures. In various embodiments, the first spring 591, the second spring 592, the third spring 593, the fourth spring 594, and the spring 595 are coil springs. In various other embodiments, they are wave springs or other types of springs. The first spring 591, the second spring 592, the third spring 593, the fourth spring 594, and the spring 595 provide for additional energy storage and return when the device 434 is used in a shoe. [0061] With reference to FIGS. 2 and 4D, the device 434 can be used in place of the device 231 in the shoe 100. In some embodiments, a corresponding bottom of each of the first spring 591, the second spring 592, the third spring 593, the fourth spring 594, and the spring 595 would be in contact with a top surface of the outsole 202 when the device 434 is positioned at least partially within the opening 217 in the midsole 203 of the shoe 100. In various embodiments, a first portion of a bottom surface of the plate 222 is glued to the top surface 581, and a second portion of the bottom surface of the plate 222 lays on a surface of the midsole 203 of the shoe 100. Also, in various embodiments, the insole 216 lays on a top surface of the plate 222. [0062] A method of using the device 434 in the shoe 100 in accordance with an embodiment includes applying force to the center portion 580 to cause force to be applied to the center portion 583, so as to cause the first flexible leg 451, the second flexible leg 452, the third flexible leg 453, and the fourth flexible leg 454 to flex to a flexed position, and to compress the first spring 591, the second spring 592, the third spring 593, the fourth spring 594, and the spring 595 so as to store potential energy. In various embodiments, the method further includes releasing the force from the center portion 580 to allow the first flexible leg 451, the second flexible leg 452, the third flexible leg 453, and the fourth flexible leg 454 to return back from the flexed position, and to allow the first spring 591, the second spring 592, the third spring 593, the fourth spring 594, and the spring 595 to expand from the compressed state so as to return energy. [0063] FIG. 6 shows a portion of an embodiment of a shoe 611 illustrating exemplary locations at which one or more devices in accordance with any of the embodiments of FIGS. 3A, 3B, 3C, 3D, 4A, 4B, 4C, and 4D may be located. Referring to FIG. 6, the shoe 611 includes a midsole 613. In various embodiments, there is an opening 617 in a forefoot portion 614 of the midsole 613. In various embodiments, there is an opening 618 in a heel portion 615 of the midsole 613. In various embodiments, there is the opening 617 in the forefoot portion 614 of the midsole 613 and the opening 618 in the heel portion 615 of the midsole 613. [0064] With reference to FIGS. 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D, and 6, in various embodiments, any of the devices 231, 232, 233, 234, 431, 432, 433, and 434 is positionable at least partially within the opening 617 in the forefoot portion 614 of the midsole 613. In various embodiments, any of the devices 231, 232, 233, 234, 431, 432, 433, and 434 is positionable at least partially within the opening 618 in the heel portion 615 of the midsole 613. In various embodiments, one device that is structured such as any of the devices 231, 232, 233, 234, 431, 432, 433, and 434 is positioned at least partially within the opening 617 in the forefoot portion 614 of the midsole 613, and another device that is structured such as any of the devices 231, 232, 233, 234, 431, 432, 433, and 434 is positioned at least partially within the opening 618 in the heel portion 615 of the midsole 613. [0065] In some embodiments, there is no opening in a heel portion of a midsole of a shoe, and there is just a device such as any of the devices 231, 232, 233, 234, 431, 432, 433, and 434 that is positioned at least partially within an opening in the forefoot portion of the midsole of the shoe. In some embodiments, there is no opening in a forefoot portion of a midsole of a shoe, and there is just a device such as any of the devices 231, 232, 233, 234, 431, 432, 433, and 434 that is positioned at least partially within an opening in a heel portion of the shoe. Any of the devices 231, 232, 233, 234, 431, 432, 433, and 434 could be located at other locations within a shoe, such as in any of a forefoot portion, ball portion, arch portion, and/or heel portion of a shoe. Also, different ones of any of the devices 231, 232, 233, 234, 431, 432, 433, and 434 could be located in a same shoe in different locations. [0066] FIG. 7 is a flowchart of a method of using a device in a shoe in accordance with an embodiment. In step 701, a force is applied to a common area at which a first flexible leg, a second flexible leg, a third flexible leg, and a fourth flexible leg of the device are joined together to cause a first spring located under a first foot connected to the first flexible leg to compress, and to cause a second spring located under a second foot connected to the second flexible leg to compress, and to cause a third spring located under a third foot connected to the third flexible leg to compress, and to cause a fourth spring located under a fourth foot connected to the fourth flexible leg to compress, and to cause a fifth spring located under the common area to compress, and to cause the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg to flex to a flexed position, so as to store potential energy. In various embodiments, the force is applied to the common area by a user of the shoe. [0067] In step 702, the force is released from the common area to allow the first spring, the second spring, the third spring, the fourth spring, and the fifth spring to stretch, and to allow the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg to return back from the flexed position, so as to return energy. [0068] FIG. 8 is a flowchart of a method of using a device in a shoe in accordance with another embodiment. The device includes a first flexible leg, a second flexible leg, a third flexible leg, and a fourth flexible leg. The first flexible leg and the third flexible leg together form a first arch. The second flexible leg and the fourth flexible leg together form a second arch. [0069] In step 801, the method includes applying a force to a center portion of the first arch to cause force to be applied to a center portion of the second arch, and to cause a first spring located under a first foot connected to the first flexible leg to compress, and to cause a second spring located under a second foot connected to the second flexible leg to compress, and to cause a third spring located under a third foot connected to the third flexible leg to compress, and to cause a fourth spring located under a fourth foot connected to the fourth flexible leg to compress, and to cause a fifth spring located under the center portion of the second arch to compress, and to cause the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg to flex to a flexed position, so as to store potential energy. In various embodiments, the force is applied to the center portion of the first arch by a user of the shoe. [0070] In step 802, the method includes releasing the force from the center portion of the first arch to allow the first spring, the second spring, the third spring, the fourth spring, and the fifth spring to stretch, and to allow the first flexible leg, the second flexible leg, the third flexible leg, and the fourth flexible leg to return back from the flexed position, so as to return energy. In various embodiments, the center portion of the second arch is located below the center portion of the first arch. [0071] The embodiments disclosed herein are to be considered in all respects as illustrative, and not restrictive of the invention. For example, in various other embodiments, additional flexible legs forming additional arches, as well as additional springs could be added to one or more of the devices. The present invention is in no way limited to the embodiments described above. Various modifications and changes may be made to the embodiments without departing from the spirit and scope of the invention.