Patent Publication Number: US-2017354258-A1

Title: Seat cushion

Description:
RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Application 62/347,888, filed Jun. 9, 2016, and U.S. Provisional Application 62/410,504 filed Oct. 20, 2016, the entire contents of each of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     Traditional sitting postures assumed when using typical office seating such as chairs has, over time, a detrimental impact on an individual&#39;s health. Besides encouraging a sedentary lifestyle, traditional seating may create muscular or orthopedic discomfort for a person. A more healthful and active seating postures, such as those provided by the upright active-sitting seat of U.S. 2013/0306831 A1 assigned to the assignee of the present application may be beneficial to a user. 
     It is generally known that the gluteus maximus muscles, which provide cover to ischial tuberosity (also known as “sitz bones”) in a standing or upright position, do not provide any cover to the sitz bones in the seated position. Further, because weight is frequently placed on the sitz bones while seated, this may cause discomfort to a person. 
     SUMMARY 
     In an aspect, this disclosure is directed to a seat cushion, comprising a first surface providing a seating surface to sit on and a second surface opposite to the first surface. The second surface can have a pair of relief pockets. The relief pockets can be offset to be depressed below a plane of the second surface so as to provide cushioning to a user&#39;s sitz bones received when the user is seated on the seating surface at a location corresponding to the relief pockets. The second surface can have variable resiliency such that a resiliency of the relief pockets is different from a resiliency of areas of the second surface surrounding the relief pocket. 
     In another aspect, the first surface and the second surface can be contoured so as to form a central core defined about a seat axis, a relief portion extending around the seat axis so as to substantially surrounding the central core, and an outer portion defined so as to surround the relief portion. The relief portion can be configured to receive and provide cushioning to a user&#39;s sitz bones received when the user is seated on the seating surface. The relief portion can be deformable when a user&#39;s weight is supported by the seating surface. The deformation of the relief portion can be substantially greater than a deformation of the central core and/or the outer portion when a force equivalent to the user&#39;s weight is applied on the central core and/or the outer portion. 
     In a further aspect, a relief portion can be shaped and sized to selectively provide cushioning to a user&#39;s sitz bones received when the user is seated on the seating surface at a location corresponding to the relief portion. The selective cushioning provided by the relief portion to the user&#39;s sitz bones can be greater than cushioning provided by the remainder of the seat cushion to portions of the user&#39;s body other than the sitz bones that are in contact with the seating surface. 
     The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a non-limiting exemplary pivot seat according to an embodiment; 
         FIG. 2  is a front perspective view of a non-limiting exemplary seat cushion according to an embodiment; 
         FIG. 3  is a cross-sectional view of the seat cushion of  FIG. 2  taken along the plane  3 - 3 ; 
         FIG. 4  is a cross-sectional view of the seat cushion of  FIG. 3  taken along the plane  4 - 4 ; 
         FIG. 5A  is a cross-sectional view of the seat cushion of  FIG. 3  taken along the plane  5 - 5  showing the relief pockets in the undeformed state; 
         FIG. 5B  is a cross-sectional view of the seat cushion of  FIG. 3  taken along the plane  5 - 5  showing the relief pockets in the deformed state when the user sits on the seat cushion; 
         FIG. 6  is a front view of the seat cushion of  FIG. 2 ; 
         FIG. 7  is a bottom view of a seat cushion according to another embodiment; and 
         FIG. 8  is a bottom perspective view of a portion of the pivot seat of  FIG. 1 ; 
         FIG. 9  is a bottom elevation view of the portion of the pivot seat illustrated in  FIG. 1 ; and 
         FIG. 10  is an exploded perspective view of the portion of the pivot seat illustrated in  FIG. 1 . 
         FIG. 11  is a front perspective view of a non-limiting exemplary pivot seat according to another embodiment; 
         FIG. 12  is an exploded perspective view of the pivot seat of  FIG. 11 ; 
         FIG. 13  is a perspective view of a seat cushion shown in  FIG. 11  according to another embodiment; 
         FIG. 14  is a bottom perspective view of the seat cushion of  FIG. 13 ; and 
         FIG. 15  is a sectional front view of the seat cushion taken along the sectional plane  15 - 15 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of a pivot seat  100  according to an embodiment. The embodiment of  FIG. 1  includes features that can optionally be provided on the embodiments of  FIGS. 2-7  or embodiments of  FIGS. 8-10 . The pivot seat  100  includes a base  102 . The base  102  of the pivot seat  100  is not illustrated in detail in  FIG. 1  and is represented as a block, to further focus on the upper portions of the seat. However, any known base  102  suitable for use with (e.g., support) such pivot seats can be used. The seat comprises a pivot post  104  that is pivotable with respect to the base  102  of the seat so as to encourage a more active seating posture. For instance, the seat would pivot toward the front such that when the user sits on the seat, their sitz bones are supported by the relief pockets of the seat cushion  130  on the seat, as will be described further below with respect to  FIGS. 2-6 . In such cases, the pivot post  104  would shift toward the front, as shown by the dashed lines in  FIG. 1 . The extent to which the pivot post  104  can pivot can be variable, thereby encouraging the user to assume a wide range of active seating postures so as to permit blood flow to the user&#39;s lower body. Such embodiments may further engage and “work” associated muscle groups. The pivot post  104  can be pneumatically adjustable to a suitable height with respect to the base  102 . 
     With continued reference to  FIG. 1 , the pivot post  104  comprises a first end  108  and a second opposite  110  to the first end  108 . The first end  108  of the pivot post  104  is pivotally coupled to the base  102 , whereas the second end  110  of the pivot post  104  is coupled to a seat pan  120 . The seat pan  120  can be connected to the pivot post  104  by a hinge mechanism  122 . Details of the hinge mechanism  122  are provided in the commonly-assigned U.S. Publication No. 2013/0306831 A1 assigned to the assignee of the present application, the disclosure of which is hereby incorporated by reference. 
     Continuing with  FIG. 1 , the seat pan  120  can be connected to a seat cushion  130 . The seat pan  120  and the seat cushion  130  can have substantially identical surface contours. For instance, the bottom surface of the seat cushion  130  and the top surface of the seat pan  120  can be substantially identical in shape and profile such that the seat pan  120  generally conforms to the shape of the seat cushion  130  (or vice versa). The seat cushion  130  can have a front edge  136  generally aligned with the front edge  138  of the seat pan  120 . The front edge  136  of the seat cushion can generally be in contact with at least a portion of the user&#39;s legs (e.g., thighs) when a user is seated on the active seating position illustrated in  FIG. 1  (dashed lines). The seat cushion  130  can have relief areas sized and shaped so as to provide optimal cushioning to the sitz bones of a person seated on the pivot seat  100  in the active seating posture indicated by the dashed lines in  FIG. 1 , as will be described further below. 
     As is apparent, the seat cushion  130  is resilient relative to the seat pan  120  and at least some portions of the seat cushion  130  can flex when a load (a user&#39;s body weight) is placed thereon. In some examples, a substantial portion (e.g., greater than about 50% of the area) of the seat cushion  130  can be resilient relative to the seat pan  120 . In other examples, the entirety of the seat cushion  130  can be resilient relative to the seat pan  120 . 
       FIG. 2  is a front perspective view of a seat cushion  10  according to an embodiment. The seat cushion  10  while illustrated as being provided on an ergonomic chair, can alternatively be provided on seats such as office chairs, car seats, bicycle seats, and other ergonomic furniture at home, in businesses or public spaces. The seat cushion  10  can be provided on the seat pan  120  (best seen in  FIG. 1 ), and be substantially similar to the seat cushion  130  illustrated in  FIG. 1 . 
     With reference to  FIG. 2 , the seat cushion  10  comprises a first surface  12  on which a user sits. The first surface  12  can be a top surface or any interior surface below the upper most surface.  FIG. 3  is a bottom view of the seat cushion  10  of  FIG. 2 . Referring now to  FIG. 3 , the seat cushion  10  comprises a second surface  14 . The second surface  14  can be a bottom surface or any interior surface spaced apart from and/or opposite to the first surface  14 . The second surface  14  comprises a plurality of connectors  16  to interface with a seat pan (e.g., such as seat pan  120  of  FIG. 1 ). Referring to  FIG. 3 , in the illustrated embodiment, the connectors  16  are buttons extending away from the second surface  14  of the seat cushion  10 . The seat pan which receives the seat cushion  10  may have complementary connectors  16  (e.g., recesses at locations corresponding to the buttons  16  of the cushion  10  on the seat pan  120 ) to receive the seat cushion  10  securely on to the seat pan  120 . Once secured, the connectors  16  may reduce relative motion (e.g., sliding) between the seat pan and the seat cushion  10 . 
     With continued reference to  FIG. 3 , the seat cushion  10  of the present embodiment includes a plurality of ribs  18  recessed from the second surface  14 . The ribs  18  are formed during fabrication of the seat cushion  10 . As mentioned earlier, the seat cushion  10  of the present embodiment is formed by molding. In one example, the seat cushion  10  may be formed by injection molding a polymer material, such as Ethylene-vinyl acetate (hereinafter, “EVA”) to form the seat cushion  10  of desired shape and size. In such embodiments, the ribs  18  facilitate flow and heat transfer during the injection molding process so as to obtain a seat cushion  10  with desired variable resiliency, as will be described further below. Other details of the injection molding process known in the art are omitted for brevity. As is apparent to one skilled in the art, injection molding EVA results in a closed-cellular foam, thereby providing advantageous properties such as resistance to water seepage and/or microbes (e.g., mold, mildew and bacteria). In some embodiments, the seat cushion  10  is fabricated as a unitary piece, and yet having portions of different resiliency or cushioning properties. Such embodiments may provide comfort to the user (due to absence of seams or ridges on the seating surface), while being durable and cost effective to fabricate. 
       FIG. 4  is a cross-sectional view of the seat cushion  10  of  FIG. 3  taken along the plane  4 - 4  seen in  FIG. 3 . As described previously, the seat cushion  10  is fabricated to have selective resiliency so as to provide support to the user seated thereon. For instance, the seat cushion  10  can be designed so as to provide cushioning to a user&#39;s sitz bones. Referring back to  FIG. 3 , the seat cushion  10  according to such embodiments include a pair of relief pockets  20  provided on the second surface  14  at a location corresponding to the location of the sitz bones in an average adult male or female user. The relief pockets  20  can have a size and shape to provide a cushioning effect to the sitz bones received and seated on the first surface  12  of the seat cushion  10 , at a lateral and longitudinal location corresponding to the relief pockets  20  (shown in  FIG. 1 ). 
     Advantageously, the seat cushion  10  according to the present embodiment is molded as a single piece, with variable resiliency at various portions of seat cushion  10 , such that different portions of the seat cushion  10  deform at different rates when a force (e.g., body weight) is applied on the seat cushion  10  (e.g., as seen in  FIGS. 5A-5B ). Referring back to  FIG. 4 , in an exemplary embodiment, the relief pockets  20  can provide greater cushioning than areas of the second surface  14  (e.g., ribs  18 ) surrounding the relief pockets  20  when a user sits thereon. In such cases, referring again to  FIG. 5B , when the relief pockets  20  deform in response to the user&#39;s weight, the deformation of the relief pockets  20  is greater than a deformation of the areas of the second surface  14  surrounding the relief pocket, when a force equivalent to the user&#39;s weight is applied on the areas of the second surface  14  surrounding the relief pocket. For instance, the areas surrounding the relief pockets  20  may have negligible deformation relative to the deformation of the relief pockets  20 , when the force equivalent to the user&#39;s weight is applied on the areas of the second surface  14  surrounding the relief pocket. In some such exemplary embodiments, the user&#39;s weight can be in the range of between about 100 pounds and about 300 pounds. As used herein, properties of the seat cushion such as resiliency, softness or cushioning of the relief pockets  20  relative to areas surrounding the relief pockets  20  can be measured and quantified by a surface hardness measuring apparatus such as a durometer. In such cases, the softness or cushioning of the relief pockets  20  measured by the durometer can be greater than those of areas surrounding the relief pockets. 
     Referring again to  FIG. 4 , a cross-sectional side view of one of the relief pockets  20  is illustrated.  FIG. 4  shows the seat cushion  10  from an inverted side view, with the second surface  14  shown above the first surface  12  for ease of illustration. However, as is apparent to one skilled in the art, the user&#39;s weight would act in the direction of the arrow “a” shown in  FIG. 4  when the user is seated on the first surface  12 . The relief pockets  20  are shaped so as to have a cushioning greater than those of areas surrounding the relief pockets  20 . In the illustrated embodiment, the relief pockets  20  can be generally symmetric about a transverse axis  24  of the seat cushion  10  but may be positioned so as to have a greater surface area near the front edge  44  than the back edge  46 . The relief pockets  20  have less material (EVA) relative to the surrounding areas  22  such that when the sitz bones apply pressure thereon (e.g., from the first surface  12 ), the shape of the relief pockets  20  permit bowing (e.g., as shown by dashed lines). While the illustrated embodiment show the relief pockets  20  to have a “kidney” shape, other shapes such as circular, oval and square are also contemplated within the scope of the present disclosure. Such embodiments advantageously permit users with different sitz bone spacing to sit on the seat cushion and experience comparable cushioning. 
     The relief pockets  20  of some exemplary embodiments may have a “shape memory” configured to permit the relief pockets  20  to support users of different body weights without having to customize the shape and size of the relief pockets  20  for each user. For instance, the relief pockets  20  may have an initial shape (shown by the solid lines in  FIG. 3 ) when the user is not seated on the seating surface, as illustrated in  FIG. 3 . As mentioned above, the relief pockets  20  have a resiliency such that the relief pockets  20  “bow”, for instance, to the exemplary shape shown by dashed lines  26  in  FIG. 4 . However, once a user seated in the seating surface rises from the seating surface the relief pockets  20  may return to their initial shape. Such embodiments may permit the seat cushion  10  to provide selective cushioning customized to users of different weights because the seat cushion  10  may return to its initial shape each time after the user&#39;s weight is removed. As mentioned above, in such cases, the areas surrounding the relief pockets  20  may have negligible deformation in response to a force equivalent to the user&#39;s weight applied thereon. 
       FIG. 5A-5B  illustrate a cross-sectional view of the seat cushion  10  of  FIG. 4  taken along the plane  5 - 5  with and without a force acting on the relief pockets, while  FIG. 6  is a front view of the seat cushion  10  of  FIG. 2 . In some embodiments, the relief pockets  20  are shaped and sized to selectively provide cushioning to the user&#39;s sitz bones received when the user is seated on the seating surface at a location corresponding to the relief pockets  20 . As mentioned previously, the cushioning provided by the relief pockets  20  to the user&#39;s sitz bones is greater than cushioning provided by the remainder of the seat cushion  10  to portions of the user&#39;s body other than the sitz bones that are in contact with the seating surface. 
     Such selective cushioning can be achieved by an appropriate shape and size of the relief pockets  20 . In one example, the relief pockets  20  are positioned to span a certain area of the second surface  14  so as to provide selective cushioning. For instance, the relief pockets  20  can occupy an area of between about 5% and about 50% of a total surface area of the second surface  14 . Relief pockets  20  sized to occupy less than about 5% of the total surface area of the second surface  14  may not provide adequate cushioning and may be too firm, while relief pockets  20  sized to occupy greater than about 50% of the total surface area of the second surface  14  may result in the rest of the seat cushion  10  deforming more than a desirable amount under the user&#39;s body weight and thereby not providing adequate support. In some embodiments, the relief pockets  20  can occupy an area of about 20% for optimal cushioning of the sitz bones while providing adequate support to the remainder of the user&#39;s body in contact with the seat cushion  10 . 
     In another example, the relief pockets  20  can be spaced such that the spacing between the two relief pockets  20  are at a certain desired value to provide selective cushioning to the sitz bones. In this example, the spacing is measured between the geometric centers of the two relief pockets  20 . For example, the spacing between the relief pockets  20  corresponds to a sitz bone spacing of an adult male or female user such that on average, the user&#39;s sitz bones rest generally at the geometric center “c” of the relief pockets  20 . In such examples, the geometric centers “c” of the relief pockets can have a spacing  42  of between about 4 inches and about 8 inches, for instance, about 6 inches. However, it is generally known that the spacing between sitz bones in some adult male users may have a standard deviation of up to about one inch toward each other relative to the average sitz bone spacing of adult male users. In such cases, the spacing  42  of the relief pockets  20  can be about 5 inches. Similarly, the spacing between sitz bones in some adult female users may have a standard deviation of up to about one inch away from each other relative to the average sitz bone spacing of adult female users. In such cases, the spacing  42  of the relief pockets  20  can be about 7 inches. Accordingly, the relief pockets  20  can be sized to accommodate a standard deviation of about +/−1 inch in the sitz bone spacing relative to the average sitz bone spacing in adult male and female users. 
     In such examples, the relief pockets  20  can have a thickness  28  of between about 20% and about 70% of thickness  30  of the seat cushion  10  to provide increased cushioning at locations corresponding to the relief pockets  20 . Further, the relief pockets  20  may have a depth  38  of between about 5% and about 50% of an overall depth  48  of the seat cushion  10 , and a width  32  of between about 5% and about 50% of an overall width  40  of the seat cushion  10 . Such exemplary embodiments with optimal size and spacing of the relief pockets  20  can advantageously accommodate users of different sizes and weight (and corresponding variability in sitz bone spacing). 
     In the illustrated embodiment, the thickness  30  of the relief pockets  20  gradually varies in the depthwise direction (e.g., along depth  38 ), as seen in  FIG. 3 . In other words, the thickness of the relief pocket  20  near the back edge  46  of the seat cushion  10  is greater than the thickness of the relief pocket near the front edge  44  of the seat cushion  10 . Further, the thickness  30  of the relief pockets  20  is generally constant along the widthwise direction (e.g., along width  32 ), as seen in  FIGS. 5A and 5B . However, in alternative embodiments, the thickness  30  of the relief pockets  20  can be generally constant in both the depthwise and widthwise directions (e.g., if the relief pockets  20  are hemispherical). Alternatively, the thickness of the relief pockets  20  can be variable along both the depthwise and widthwise directions when relief pockets  20  of other shapes are used. The relief pocket dimensions described herein provide optimal cushioning and selective resiliency as described in various embodiments herein. 
     Referring back to  FIGS. 2 and 4 , the relief pockets  20  are positioned in the depthwise direction to be proximal to the front edge  44  than the back edge  46  of the seat cushion  10 . For example, the geometric center “c” of the relief pockets  20  may be positioned to the front of the transverse axis  24  of the seat cushion  10 . It is worthwhile mentioning that the geometric center of the relief pockets  20  may or may not coincide with the point of minimum thickness. In some examples, if the geometric center does not coincide with the point of minimum thickness of the relief pocket, the point of minimum thickness may be positioned to the front of the transverse axis  24  of the seat cushion  10 . Such embodiments permit the user to sit in a more active or neutral sitting posture. For example, seat cushions according to some such embodiments may be suitable for use with an upright active-sitting seat illustrated in  FIG. 1 , whereby the user sits more toward the front end of the seat (e.g., near edge  138 ) to reduce some of the discomfort and health hazards associated with traditional seating. Such upright active seats encourage better blood circulation and improve concentration and alertness. Seat cushions illustrated herein can, of course, be used with other seats such as traditional office chairs, car seats, bicycle seats, household furniture and the like. 
       FIG. 7  is a bottom view of a seat cushion  200  according to another embodiment. The embodiment of  FIG. 7  may be substantially similar to that of  FIGS. 2-6 . The seat cushion  200  shown in  FIG. 7  can have pin holes  202  instead of ribs  18  to facilitate heat transfer (e.g., cooling) during fabrication (e.g., injection molding) of the seat cushion  10 . Similar to the ribs  18 , however, the pin holes  202  are generally rigid and have a lower resiliency relative to the relief pockets  20 , such that they do not deform to the same extent as the relief pocket  20  when a force equivalent to the user&#39;s weight is applied thereon. While not illustrated, the embodiments of  FIG. 7  may also have other structural differences such as size, shape and location of the relief pockets  20 , but may provide substantially the same amount of cushioning as the relief pockets  20  shown in  FIGS. 2-6 . 
       FIGS. 8-10  illustrate various views of a seat pan  220  and a seat cushion  230  according to another embodiment. The seat pan  220  and the seat cushion  230  can be substantially similar to the seat cushion  130 ,  10  and  200  illustrated in  FIGS. 1, 2-6 and 7  respectively. The seat cushion  230  as illustrated in  FIG. 8  can have a waterfall edge. For instance, the seat cushion  230  can be of dimensions so as to have a bottom surface contour that generally matches a top surface contour of the seat pan  220  (as is the case with seat cushions  130 ,  10  and  200 ). In addition, the depth  232  of the seat cushion  230  can be greater than the depth  234  of the seat pan  220 . The seat cushion  230  therefore has a front edge  236  that extends past the front edge  238  of the seat pan  220 . 
     Referring now to  FIG. 9 , portions of the seat cushion  230  can be cantilevered to provide relief to the back of a user&#39;s legs and reduce the chances of portions of the user&#39;s legs from being pinched. For instance, at least the front edge  236  of the seat cushion can be cantilevered relative to the seat pan  220 . The seat pan  220  has a seat pan depth  234  and a seat pan width  239 , and the seat cushion  230  has a seat cushion depth  232  and the seat cushion width  240 . The seat pan width  239  generally equals the seat cushion width  240 . For instance, the front edge  236  of the seat cushion extends over a substantial portion (e.g., at least 70%) of the front edge  238  of the seat pan. The seat pan depth  234  is generally less than the seat cushion depth  232 . The seat pan width  239  and the seat cushion width  240  can be generally variable along the depthwise (e.g., front-back in the illustrated embodiment of  FIG. 9 ) direction, but generally follow the same contour such that at any location in the depthwise direction, the seat pan width  239  equals the seat cushion width  240 . Similarly, seat cushion depth  232  and the seat pan depth  234  can generally vary in the widthwise (e.g., right-left in the illustrated embodiment of  FIG. 9 ) direction. In the embodiments of  FIGS. 8-10  however, the seat pan depth  234  is generally less than the seat cushion depth  232  at any point on the widthwise direction. Further, the difference between the seat cushion depth  232  and the seat pan depth  234  can be defined as an offset distance  242 . The offset distance  242  can be generally constant along the widthwise direction (e.g., between the right edge  244  and the left edge  246 ) in such embodiments except near the right edge  244  and the left edge  246  as shown in  FIG. 9 . 
     The offset distance  242  is generally non-zero, and in some examples, extends between about 15 millimeters and about 35 millimeters, and preferably about 20 millimeters and about 25 millimeters. In the illustrated embodiment, the offset distance  242  is about 30 millimeters. In some such cases, the offset distance  242  permits the front edge  236  of the seat cushion  230  to act as a cantilevered edge, as the seat cushion is made of a material such as injection molded EVA. Such embodiments provide optimal amount of relief to the back of a user&#39;s legs while generally supporting the user&#39;s weight thereon. 
     As perhaps best seen in  FIG. 10 , the seat pan  220  can generally conform to the shape of the seat cushion  230  and support the seat cushion  230 . The seat pan  220  can be rigid relative to the seat cushion  230 . Accordingly, the waterfall edge design of the seat cushion  230  can provide relief to portions of a user&#39;s legs when seated on the pivot seat  100 . For instance, when a user is seated in the active seating posture (illustrated by the dashed lines in  FIG. 1 ), the front edge  236  of the seat cushion  230  shown in  FIGS. 8-10  (that extends past the front edge  238  of the seat pan  220 ) rests against the underside of a user&#39;s thighs. As the seat cushion  230  is resilient relative to the seat pan  220 , the front edge  236  of the seat cushion  230  may not cause a pinch point on the underside of the user&#39;s thighs, and provide cushioning thereto when the user&#39;s body weight is rested on the seat cushion  230 . The front edge  236  of the seat cushion  230  is therefore softer (e.g., more deformable) relative to the front edge  238  of the seat pan  220  when a user&#39;s weight is applied on the seat cushion  230 . 
     With continued reference to  FIGS. 9 and 10 , the seat cushion  230  comprises a plurality of connectors  250  to interface with the seat pan  220 . The connectors  250  of the seat cushion  230  can engage with complementary connectors  250  of the seat pan  220  so as to rigidly connect thereto. In the illustrated embodiment, the connectors  250  are ribs that protrude outward from a second surface  252  of the seat cushion  230 . As seen in  FIG. 10 , the seat pan  220  can have apertures  262  that are sized and shaped to receive the ribs of the seat cushion  230 . The apertures  262  are positioned such that when the ribs are pushed therethrough, the seat cushion  230  may not move with respect to the seat pan  220 . Further, the position of the apertures  262  and the ribs can be positioned and oriented such that the front edge of the seat cushion  230  extends past the front edge of the seat pan  220  when the ribs  250  of the seat cushion  230  are pushed through the apertures  262  of the seat pan  220 . 
       FIG. 11  illustrates a pivot seat  300  according to another embodiment. The pivot seat  300  can be substantially similar to the pivot seat  100  illustrated in  FIG. 1 . Referring to  FIG. 11 , the pivot seat  300  can be rotationally symmetric about a seat axis  302 . Such embodiments permit the user to use the pivot seat in any rotational orientation about the seat axis  302 . With continued reference to  FIG. 11  and referencing the exploded perspective view of  FIG. 12 , the pivot seat  300  comprises a base  304 . As is appreciable from  FIGS. 11 and 12 , the base  304  can have a non-planar portion  344  contacting a floor surface. For example, the base  304  can be hemispherical. Alternatively, the base  304  can be curved so as to have an apex that can contact the floor surface. The base  304  can thus pivot toward the floor surface, thereby permitting the user to assume an active seating posture. 
     Referring to  FIGS. 11 and 12 , the pivot seat  300  includes a seat post  306 . The seat post  306  can be recessed within a seat body portion  308 . The seat post  306  can include a first end  310 , and a second end  312  opposite to the first end  310 . The first end  310  of the seat post  306  can be connected to the base  304 , and the second end  312  can be connected to a seat pan  320 . The seat pan  320  can also optionally include a handle (illustrated as a loop in  FIGS. 11 and 12 ) to permit a user to transport the seat to different locations. 
     The seat pan  320  can be disc-shaped and have a planar first surface  322  (e.g., top surface) on which a seat cushion  330  is positioned (e.g., attached adhesively, or by mechanical fasteners). The seat cushion  330  may have a contoured profile to permit selective cushioning of certain areas of a user&#39;s body (e.g., sitz bones), however, the seat pan  320  may not follow the contours the seat cushion  330 . The seat pan  320  can be rigid relative to the seat cushion  330 , and may thus act as a support surface for mounting the seat cushion  330 . 
       FIGS. 13-15  illustrate various views of the seat cushion  330 . The seat cushion  330  can be substantially rotationally symmetric about the seat axis  302 , so as to permit the user to sit in any desired rotational orientation (e.g., 360 degrees about the seat axis  302 ). As described previously with respect to seat cushions  10 ,  200  and  230 , the seat cushion  330  can be resilient relative to the seat pan  320  and contoured to selectively provide increased cushioning for the user&#39;s sitz bones. 
     In some such examples, the seat cushion  330  can have a central core  332 . The central core  332  can be surrounded by a relief portion  336 . The relief portion  336  can be surrounded by an outer portion  338 . The seat cushion  330  can have a first surface  340  (e.g., top surface or an interior surface below the top surface) providing a seating surface for the user to sit on and a second surface  342  (e.g., bottom surface or an interior surface above the bottom surface) opposite to the first surface  340 . The first surface  340  can be contoured such that a portion  344  of the first surface  340  corresponding to the central core  332  can be concave, and a portion  346  of the second surface  342  corresponding to the central core  332  can be convex or generally planar when viewed from a plane parallel to the seat axis  302  (e.g., when viewed from the front, as shown in  FIG. 15 , or from the sides lateral to the view shown in  FIG. 15 ). Such contouring may facilitate ease of manufacturing (e.g., molding) the material (e.g., EVA foam) of the seat cushion  330 . 
     The relief portion  336  can be rotationally symmetric so as to substantially surround the central core  332 , which may permit cushioning of sitz bones regardless of the rotational orientation in which the user is seated. The relief portion  336  can also be contoured to provide selective cushioning. For instance, the relief portion  336  can be contoured such that it deforms to a greater extent when a user&#39;s weight acts on the relief portion  336 , relative to the deformation of the central core  332  and/or the outer portion  338  when a force equivalent to the user&#39;s weight acts on the central core  332  and/or the outer portion  338 . 
     The relief portion  336  can be sized and positioned so as to accommodate different user sizes and sitz bone spacing (e.g., as described with respect to  FIGS. 3-6 ). Returning to  FIGS. 14 and 15 , the relief portion  336  can have a relief portion width  348  that can be between about 20% and about 70% of a representative dimension  350  (e.g., radius) of the seat cushion  330  to accommodate variability in sitz bone size and spacing, as described previously. Further, the seat cushion  330  can have an overall thickness  352  defined between a first extremity  354  on the first surface  340  and a second extremity  356  on the second surface  342 . The first extremity  354  can be an uppermost point of the first surface  340  (e.g., top surface) and the second extremity  356  can be a lowermost point of the second surface  342  (e.g., bottom surface). A thickness  358  of the relief portion  336  can be between about 20% and about 70% of the overall thickness  352 . In the illustrated embodiment, the thickness  358  of the relief portion  336  is about 50% of the overall thickness  352 . Higher values of thickness  358  of the relief portion  336  may provide less cushioning, whereas lower values of thickness  358  of the relief portion  336  may lead to less support. 
     As noted above, the relief portion  336  can be contoured so as to provide selective cushioning of certain areas (e.g., sitz bones) of the user&#39;s lower body. In an example, the first surface  340  corresponding to the relief portion  336  can be generally convex when viewed from a plane parallel to the seat axis  302 . Correspondingly, the second surface  342  at a location corresponding to the relief portion  336  can be generally convex when viewed from a plane parallel to the seat axis  302 . The contouring of the first surface  340  can advantageously result in receiving, and thereby making contact with the sitz bones, which may often be the lowest portion of the user&#39;s lower body when in a seated posture. Such contouring may permit the relief portion  336  to advantageously deform to a greater extent relative to areas surrounding the relief portion  336  (e.g., central core  332  and outer portion  338 ) when a user&#39;s weight is placed thereon, as described with respect to similarly contoured seat cushion  10  shown in  FIGS. 2-6 . 
     Referring again to  FIG. 15 , the second surface  342  can have areas that separate the relief portion  336  from the central core  332 . One such area can be contact portions  360 ,  362 ,  366  and  368  that are generally planar so as to contact a generally planar first surface  322  of the seat pan  320  (shown in  FIG. 12 ). As is appreciable, the contact portions  360 ,  362 ,  366  and  368  can generally form a second extremity  356  of the second surface  342 , and be generally coplanar with each other. 
     Advantageously, the seat cushion  330  can be formed as a unitary piece using injected molding a suitable material (e.g., EVA). Accordingly, the convex portions of the central core  332 , the convex portions of the relief portion  336  and the contact portions  360  can be a single continuous surface contoured as described above. 
     Embodiments of the present disclosure provide several advantages. Seat cushions according to the disclosed embodiments provide selective cushioning such that the relief pockets provide cushioning to the sitz bones for the user which are frequently uncovered by the user&#39;s muscles (e.g., gluteus maximus) when the user is in a seated position. The seat cushions are made of injection molded EVA, which is durable and cost effective to fabricate. The seat cushions are of a generally unitary construction (e.g., made of a single piece) despite having selective or variable resiliency at various portions of the seat cushion, which reduces discomfort associated with seat cushions fabricated from several pieces of foam that are attached together. Further, the relief pockets of the seat cushions are sized to accommodate a variety of sitz bone spacing, and are fabricated from polymers that have a desired shape memory to accommodate a wide range of user weights without having to size the cushions for each individual user. Additionally, embodiments that include a waterfall edge design on the seat cushion additionally provide further cushioning of the underside of a user&#39;s thighs when seated in the active or upright position. Further, embodiments also permit the seat cushion to be used in any rotational orientation. 
     Various examples have been described. These and other examples are within the scope of the following claims.