in the summary above and in the detailed description of preferred embodiments , reference is made to particular features ( including method steps ) of the invention . where a particular feature is disclosed in the context of a particular aspect or embodiment of the invention , that feature can also be used , to the extent possible , in combination with and / or in the context of other particular aspects and embodiments of the invention , and in the invention generally . the term “ comprises ” is used herein to mean that other ingredients , features , steps , etc . are optionally present . when reference is made herein to a method comprising two or more defined steps , the steps can be carried in any order or simultaneously ( except where the context excludes that possibility ), and the method can include one or more steps which are carried out before any of the defined steps , between two of the defined steps , or after all of the defined steps ( except where the context excludes that possibility ). in this section , the invention will be described more fully with reference to certain preferred embodiments . this invention may , however , be embodied in many different forms and should not be construed as limited to the embodiments set forth herein . rather , these embodiments are provided so that this disclosure will convey preferred embodiments of the invention to those skilled in the art . fig1 generally illustrates a prosthetic foot 20 according to an embodiment of the invention . the foot 20 includes a forefoot member 30 , a heel member 60 , and an ankle member 90 . in practice , the foot 20 is attached to a limb connector 130 designed to connect the foot to the wearer &# 39 ; s leg . the wearer &# 39 ; s leg defines a vertical axis l along which the ankle member 90 is aligned . the limb connector 130 is shown in broken lines to indicate that its design does not form a key component of the foot 20 . the foot 20 may function regardless of the type of limb connector 130 used . the prosthetic foot 20 is modular and includes parts that can be removed and substituted very easily to meet the individual needs of the wearer . this allows the components to be interchanged with other components for the purpose of replacement or for the purpose of substituting one component for another component having different properties . for example , the original forefoot and heel members may be interchanged with different forefoot and heel members suited to a particular activity , the wearer &# 39 ; s gait , the wearer &# 39 ; s lifestyle , a particular shoe size , the wearer &# 39 ; s height , the wearer &# 39 ; s weight . in fig2 and 3 the facing side of the ankle member is cutaway so that the mechanical functionality of various components is revealed . the details of each component are discussed in turn . the ankle member 90 forms a sleeve into which a forefoot member shaft 32 and heel member shaft 62 are positioned . the ankle member 90 applies inward force against the forefoot member shaft 32 and heel member shaft 62 to maintain alignment of the respective shafts 32 , 62 along the vertical axis of the ankle member 90 . the forefoot member shaft 32 and heel member shaft 62 slide independently along the ankle member when upward force acts on the forefoot member 30 or heel member 60 . a compressible member 110 is coupled to the ankle member 90 and is in compressible contact with the heel member shaft 62 and forefoot member shaft 32 so as to compress when upward force acts on the heel member 60 and / or forefoot member 30 . the vertical arrow a in fig2 and 3 illustrates that the compressible member 110 compresses along the direction of the vertical axis of the ankle member 90 . the vertical arrows b and c illustrate the direction the shafts 32 , 62 slide along the ankle member 90 . when upward force acts on the heel member 60 or forefoot member 30 , the respective shaft 32 , 62 slides vertically within the ankle member 90 and compresses the compressible member 110 , which absorbs the shock due to the force . the heel member shaft 62 and forefoot member shaft 32 slide independently of one another along the ankle member 90 because the only mechanical link between the shafts 32 , 62 is the inward force applied by ankle member 90 . the heel member 60 can easily be removed from the ankle member 90 by sliding it out of the ankle member 90 . likewise , the forefoot member 32 can easily be removed from the ankle member 90 by sliding it out of the ankle member 90 . either of these components can then be replaced with a different heel member 60 and / or forefoot member 30 that suits a certain activity or weight without needing to remove the ankle member 90 from the wearer &# 39 ; s limb . this also allows worn components to be replaced without needing to replace the entire foot or send the foot back to the manufacturer for repair . additional details of a preferred forefoot member 30 are shown in fig4 - 8 . the forefoot member 30 includes the forefoot member shaft 32 and extends from a forefoot member upper end 34 through a curved forefoot section 36 to a toe section end 38 and terminates at a toe end 40 . a forefoot member top surface 42 and forefoot member bottom surface 44 are positioned on opposite sides . at the shaft section 32 , the forefoot member top surface 42 includes a lubricated forefoot member anterior surface 46 . also at the shaft section 32 , the forefoot member bottom surface 44 includes a lubricated forefoot member posterior surface 48 . the opposed lateral sides of the forefoot member each include an elongated depression 50 formed along the shaft 32 adjacent to the lubricated forefoot member posterior surface 48 . additional details of a preferred heel member 60 are shown in fig9 - 13 . the heel member 60 includes the heel member shaft 62 and extends from a heel member upper end 64 through a curved heel section 72 to a heel end 66 . a heel member top surface 68 and heel member bottom surface 70 are positioned on opposite sides . at the shaft section 62 , the heel member top surface 68 includes a lubricated heel member posterior surface 74 . also at the shaft section 62 , the heel member bottom surface 70 includes a lubricated heel member anterior surface 76 . the opposed lateral sides of the heel member 60 each include an elongated depression 78 formed along the shaft 62 adjacent to the lubricated heel member anterior surface 76 . additional details of a preferred ankle member 90 are shown in fig1 - 17 . the ankle member 90 forms a sleeve having opposed anterior and posterior sidewalls 92 a and opposed lateral side walls 92 b that together define an interior 100 . the interior surface along the anterior and posterior sidewalls 92 a is lubricated to form anterior and posterior lubricated sidewalls 104 . in the embodiment shown , the ankle member 90 is symmetric about a vertical plane bisecting the anterior and posterior sidewalls 92 a and a vertical plane bisecting the lateral side walls 92 b . both lateral sidewalls 92 b define a respective opening 102 that passes through to the interior 100 . the purpose of the openings 102 is described in detail below . additional details of the preferred compressible member 110 are shown in fig1 and 19 . the compressible member 110 is adapted to compress in the vertical direction and return to its original shape when the compression force is removed . accordingly , the compressible member 110 functions in a spring - like manner to absorb the shock on the heel member 60 and forefoot member 30 when the wearer uses the prosthetic foot . in the example shown , the compressible member 110 forms an elongated disk - like shape with a compressible material 112 in a high flexure and fatigue resistant material sheath 114 . the compressible material 112 is preferably rubber , plastic , or the like . the sheath 114 is preferably also rubber , plastic , or the like . the make - up of the compressible material 112 is specifically selected for the degree of energy recovery required to match the wearer &# 39 ; s lifestyle and body weight . the material property combinations for the compressible material 112 material and sheath 114 determine the energy recovery performance of the compressible member 110 . these materials may be selected to provide a specific type of shock - absorbing performance tuned to a wearer &# 39 ; s preference . when the compressible member 110 compresses , it recovers energy from the heel member 60 and forefoot member 30 and returns a significant amount of that energy back to the heel member 60 and forefoot member 30 to allow the wearer to have a more natural stride . the compressible member 110 also returns rapid shock induced energy , from jumping for example , in a controlled manner . if the compressible member 110 becomes overloaded or fatigued and the sheath 114 fails , the compressible member 110 will not totally fail because the compressible material 112 will remain intact . the shape of the compressible member 110 is selected to fit within the interior 100 of the ankle member 90 so that when the compressible member 110 is compressed , it deforms and presses against the interior sidewalls 92 a , b of the ankle member , which , in turn , maintain its alignment with the forefoot member 30 and heel member 60 . for this reason , it is preferred that the height h , width w , and thickness t of the compressible member 110 be such that it fits snugly within the ankle member 90 so that the ankle member &# 39 ; s interior walls either touch it or nearly touch it when the compressible member 110 is not compressed . the preferred arrangement of the compressible member 110 with respect to the ankle member 90 is best shown in fig2 and 3 . the shape of the compressible member 110 can be altered to correspond to the shape of the interior 100 of the ankle member 90 . accordingly , the compressible member 110 need not have the shape shown in every embodiment . limiting the lateral expansion of the compressible member 110 within the ankle member 90 is advantageous for many reasons , which include preventing destructive overstressing of the sheath 114 and changing the wearer &# 39 ; s “ feel ” while walking to identify the need to replace the compressible member 110 . although the compressible member 110 shown in the drawings and described here is particularly preferred , the compressible member 110 is not limited to this specific example . there are various other types of spring - like or shock absorbing devices that one having skill in the art , using this disclosure as guidance , may use to serve the same purpose . referring back now to fig2 , when the forefoot member 30 and heel member 60 are coupled to the ankle member 90 the lubricated posterior heel member surface 74 is in slidable contact with the ankle member posterior lubricated sidewall 104 , the lubricated anterior forefoot member surface 46 is in slidable contact with the ankle member anterior lubricated sidewall 104 , and the lubricated posterior forefoot member surface 48 is in slidable contact with the lubricated anterior heel member surface 76 . the lubricated surfaces are preferably formed from a solid lubricating material inlaid into the material that makes up the respective component part . the lubricating material allows the surfaces to slide quietly against each other with little wear . a particularly preferred lubricating material is polytetrafluoroethylene , commonly sold under the name teflon ® by e . i . dupont de nemours and company , corp . other suitable lubricating materials include , but are not limited toother families of fluoropolymers , polyethylene polymers of various molecular weights , acetal resins ( commonly sold under the name delrin ® by e . i . dupont de nemours and company , corp ), or any other polymer that has good resistance to wear due to sliding . although not preferable , if desired , a liquid or gel - type lubricant can be applied to the lubricated surfaces for extra lubrication . one must be careful , however , in choosing the lubricant because grit trapped in the lubricant may damage the solid lubricating material . as shown in fig1 and 2 , pins 120 are positioned through the opposed lateral sidewalls 92 b of the ankle member 90 . preferred pins 120 are shown in greater detail in fig2 - 23 . each pin 120 includes a cylindrical body 122 extending from a first end 123 to a wedge shaped second end 124 . the pins 120 are preferably made from the same lubricating material as the lubricated surfaces , most preferably polytetrafluoroethylene , to allow the wedge shaped second end 124 to slide easily against the heel member 90 and forefoot member 30 . as best shown in fig2 and 24 a - c , within the ankle member 90 , the respective depressions 50 , 78 of the forefoot member 30 and heel member 60 meet to form a pair of vertical guide slots that define the sliding direction in which the forefoot member 30 and heel member 60 slide . as best shown in fig3 , the pins 120 are positioned through the openings 102 in the ankle member 90 so that the wedge shaped second end 124 of each pin 102 fits within a respective guide slot . the pins 120 restrict the distance the forefoot member 30 and heel member 90 can slide to the length of the guide slots . as mentioned above , the various components of the prosthetic foot 20 can easily be removed from the ankle member 90 without removing the ankle member 90 from the wearer &# 39 ; s leg . this is advantageous for many reasons , some of which have already been described . one of the particular advantages of the foot &# 39 ; s modularity is that is allows one to easily replace the heel member 60 and forefoot member 30 . an example of this is illustrated in fig2 a - c in which a height of the heel end above ground g is adjusted by replacing heel member 60 ′ with shorter heel member 60 ″. this is achieved by sliding heel member 60 ′ out of the ankle member 90 and sliding heel member 60 ″ into the ankle member 90 as illustrated by the arrows in fig2 b . the guide pins ( not shown ) are installed as previously described . fig2 c shows the shorter heel member 60 ″ installed on the prosthetic foot 20 . referring now to fig2 , it may be useful to include a pin securing member 140 to maintain the position of the pins 120 . in the example shown , the pin securing member 140 is an annular strap that extends completely around the ankle member 90 and presses inwardly on the pins 120 . there many different strap - type pin securing members 140 that are suitable , including resilient straps that can be stretched over the pins 120 or belt - like straps that include a fastener for joining two ends together . a preferred pin securing member 140 is a belt - like strap with a hook and loop type fastener . when used , the pin securing member 140 is preferably tightened around the pins 120 to prevent the pins from sliding out of the openings 102 while pressing the second end 124 of the pins 120 into the guide slots , which , in turn , causes the anterior lubricious surface 46 of the forefoot member and the posterior lubricious surface 74 of the heel member 90 to press against the lubricious surfaces 104 on the interior of the ankle member 90 . the prosthetic foot 20 may be made from any material suitable for making components parts of prosthetic devices and that can allow each of the components to perform its desired functions . the forefoot member 30 , heel member 60 , and ankle member 90 may be primarily made of the same or a different material . a particularly preferred material for making the forefoot member 30 , heel member 60 , and ankle member 90 is carbon fiber composite because it is lightweight , strong , and resilient . the properties of carbon fiber are also tunable to meet a desired need by varying the ply schedule , layer orientation , resins , and fabrication process employed to make each part . the scope of the invention is not limited to the particular shape of the component shown in the drawings and described . the shape of each component may vary to account for a wearer &# 39 ; s activity level and / or weight or may vary to be suited to a particular activity such as running . the invention has been described in some detail , but it will be apparent that various modifications and changes can be made within the spirit and scope of the invention as described in the foregoing specification and the appended claims .
a prosthetic foot includes a heel member having a heel member shaft extending upwardly from a heel end thereof and a forefoot member having a forefoot member shaft extending upwardly from a toe end thereof . an ankle member receives the heel member shaft and forefoot member shaft so as to allow the heel member shaft and forefoot member shaft to translate in a direction of a wearer &# 39 ; s leg in response to an upward force thereon . at least one compressible member is coupled to the ankle member and is in compressible contact with the heel member shaft and / or forefoot member shaft so as to compress in response to the translation thereof .