Abstract: A prosthetic joint can include a first attachment member and a second attachment member coupled to the first attachment member. The second attachment member can include a cylindrical chamber. The prosthetic joint can include a fixation system disposed within the cylindrical chamber comprising at least one cam. The prosthetic joint can have an unlocked configuration, wherein in the unlocked configuration the first attachment member and the second attachment member can rotate relative to each other. The prosthetic joint can have a locked configuration, wherein in the locked configuration the first attachment member is substantially prevented from rotating relative to the second attachment member.

Abstract: A prosthetic foot is provided with a forefoot spring, a heel spring and a base spring. The base spring is connected to the heel spring and to the forefoot spring. The base spring has receiving means for the forefoot spring and the heel spring, into which receiving means the heel spring and the forefoot spring can be inserted. The heel spring is connected to the forefoot spring via a coupling element, and the coupling element extends forwards along the forefoot spring at least via one portion thereof.

Abstract: A prosthetic system includes a prosthetic foot with a foot member defining a first end portion, a second end portion, and an intermediate portion defining a curvature and extending between the first and second end portions. A pump mechanism is coupled to the foot member. The pump mechanism includes a housing defining a cavity, and a membrane situated in the cavity. The pump mechanism is movable between an original configuration and an expanded configuration. A movable member includes a first portion coupled to the membrane and a second portion arranged to slidably engage the foot member. Relative movement between the first and second end portions moves the first portion of the movable member relative to the housing and slides the second portion along a length of the foot member to shift the pump mechanism between the original and expanded configurations.

Abstract: A prosthetic device includes a phalanges portion, a metatarsals portion that is movably coupled to the phalanges portion, an ankle portion that is movably coupled to the metatarsals portion, and a calcaneus portion that is movably coupled to the ankle portion.

Abstract: A prosthetic foot can include an attachment member, at least one first brace, at least one first flexible member, an unpowered actuator, at least one second brace, and at least one second flexible member. The attachment member can include a connector configured to connect the attachment member to a user or another prosthetic device. The at least one first brace can mount to the attachment member and the at least one first flexible member can connect to the attachment member by the at least one first brace such that a force between the ground and the attachment member can be supported by the at least one first flexible member. The unpowered actuator can mount to the attachment member and the at least one second brace can be mounted to the actuator. The at least one second flexible member can connect to the attachment member by the at least one second brace such that a force between the ground and the attachment member can be supported by the at least one second flexible member.

Abstract: A prosthetic ankle module allows for translational and/or rotational movement of a prosthetic foot relative to an adapter. The ankle module can include a four-bar linkage assembly. Links of the linkage assembly can be arranged in various configurations, e.g., parallel or non-parallel and having equal or non-equal lengths, to provide different functions and benefits, e.g., dorsiflexion, plantar flexion, vertical shock absorption, inversion, eversion, and/or rotation about the sagittal axis. Other types of linkage assemblies are also possible. A prosthetic foot can further include a support spring to limit the range of motion of the adapter in use.

Abstract: Implementations of a quasi-passive assistive device are disclosed. Such a device may comprise a spring mechanism that increases stiffness similar to a biological ankle. In one implementation, the spring mechanism may comprise a piston, valve, springs, or other elements to match a biological stiffness profile similar to that of a biological ankle. In one implementation, an apparatus for an artificial ankle is disclosed, comprising a piston coupled to a spring and the piston connected to a valve. The spring and the piston may store energy during dorsiflexion of the ankle and the spring and the piston release energy during plantarflexion of the ankle. The piston may store and release energy through the use of the valve.

Abstract: A foot prosthesis that includes at least one spring element, an attachment member, and a heel member. The at least one spring element has a toe end portion, a heel end portion, an upper surface, and a lower surface. The attachment member is mounted to the upper surface and is configured to connect the foot prosthesis to a lower limb prosthesis component. A position of the attachment member is adjustable along a length of the at least one spring element. The heel member is mounted below the lower surface of the at least one spring element, and a position of the heel member is adjustable along the length of the at least one spring element.

Abstract: A hollow tubulous composite structure and method for prosthetic limbs is described.

Abstract: Prosthetic feet that provide for variable and adjustable stiffness are provided. A foot element can include a tongue portion defined or formed by a slot in the foot element that at least partially separates the tongue portion from a remainder of the foot element. The tongue portion can be operably connected to the remainder of the foot member to increase the stiffness of the foot member or operably disconnected from the remainder of the foot member to increase the flexibility of the foot member. The prosthetic foot further includes a mechanism for adjusting whether the tongue portion is operably connected or disconnected from the remainder of the foot member. The mechanism can be selectively actuated to adjust the stiffness of the foot element in dorsiflexion and/or plantarflexion and/or to adjust the degree to which the tongue portion is allowed to flex relative to the remainder of the foot member.

Abstract: A device is provided including a first linkage system and a second linkage system. Each linkage system may include an upper support, a lower support, and a cross bar linkage including a first cross bar and a second cross bar. The first cross bar may be configured with a first end pivotally coupled to a first end of the lower support and a second end pivotally coupled to a second end of the upper support. The second cross bar may be configured with a first end pivotally coupled to a second end of the lower support and a second end pivotally coupled to a first end of the upper support. The device may also include a flexible bridging platform coupled to one of the upper support or the lower support of the first linkage system and coupled to the upper support of the second linkage system, and a flexible strut coupled to the lower support of the second linkage system.

Abstract: An artificial foot having a longitudinal axis extending from a heel area to a toe area, a length, a width and a height is provided. The artificial foot includes a connection to a lower leg part, an upper supporting structure in the direction of height, an elastic sole structure extending from the heel area to the toe area, an elastic connecting element arranged between the upper supporting structure and the sole structure, and a coupling system. The upper supporting structure is connected to the sole structure approximately in a middle of the foot with respect to its length by means of the coupling system. The coupling system allows a relative tilting motion between the upper supporting structure and the sole structure while keeping a distance between the upper supporting structure and the sole structure in a middle of the coupling system constant, at least while a patient places weight on it when standing.

Abstract: There is provided a movement support apparatus including a lower limb coupling portion configured to be coupled to a lower limb, an elastic member, a ground contact unit configured to include a ground contact plate coming into contact with a surface and a transmission portion transmitting force generated by the elastic member, and an ankle portion configured to be installed between the lower limb coupling portion and the ground contact unit. The ground contact unit is installed to be displaceable between a position at which the transmission portion comes into contact with the ankle portion and a position at which the transmission portion is uncoupled from the ankle portion.

Abstract: Systems and apparatuses are provided comprising a prosthetic foot, a shock absorbing module and a coupling member for operably connecting the prosthetic foot to the shock absorbing module. The prosthetic foot can include an upper member connected to a lower member, wherein the upper member includes an upper attachment portion for attaching to the coupling member. The coupling member can include one or more holes for receiving an epoxy filling to secure the coupling member to the upper attachment portion of the prosthetic foot. The shock absorbing member can include a threaded portion that is mateable with an inner threaded section of the coupling member, thereby allowing height adjustability of the shock absorbing member.

Abstract: 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'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.

Abstract: A clamp for a prosthetic limb includes a first section configured to couple to a first portion of a prosthetic limb and a second section being separate and spaced apart from the first section and configured to couple to a second portion of a prosthetic limb. The clamp further includes a plurality of pins extending between the first section and the second section and connecting the first section to the second section, each pin having a first end connected to the first section and a second end opposite to the first end and connected to the second section.

Abstract: A range of motion (ROM) prosthetic foot and passive dampening ankle joint have limited dorsiflexion-plantarflexion (up and down) pivoting to accommodate different environments, and a spring to provide resilient resistance to plantarflexion (or lowering of the toe), and to bias the foot in dorsiflexion (or raising the toe). The ankle joint has a rear pivot rearward of a hydraulic link for a smooth feel. The ankle joint has an internal bumper in a hydraulic cylinder for a smooth feel. The ankle joint has an internal hydraulic compensator disposed in the cylinder and carried by the piston to equalize volume.

Abstract: 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'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.

Abstract: There is provided a movement support apparatus including a lower limb coupling portion configured to be coupled to a lower limb, an elastic member, a ground contact unit configured to include a ground contact plate coming into contact with a surface and a transmission portion transmitting force generated by the elastic member, and an ankle portion configured to be installed between the lower limb coupling portion and the ground contact unit. The ground contact unit is installed to be displaceable between a position at which the transmission portion comes into contact with the ankle portion and a position at which the transmission portion is uncoupled from the ankle portion.

Abstract: A stable shock absorbing prosthetic foot that transfers energy between heel strike and toe-off. A toe plate is separated from one or more other plates by a bumper assembly located at each of the toe end and heel end of the foot. Certain embodiments of the shock absorbing foot of the present invention are designed for use with a prosthetic ankle. A torsion adapter may also be used to attach a prosthetic foot of the present invention to the remainder of a prosthesis.

Abstract: 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'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.

Abstract: A low profile prosthetic foot comprises a foot member extending at an incline from an anterior portion to a posterior portion thereof and configured to flex during motion, and an adapter mounted solely at a posterior section thereof to the posterior portion of the foot member so that the adapter's anterior section can move relative to the foot member and “roll-up” onto the foot member during motion.

Abstract: A range of motion (ROM) prosthetic foot and passive dampening ankle joint have limited dorsiflexion-plantarflexion (up and down) pivoting to accommodate different environments, and a spring to provide resilient resistance to plantarflexion (or lowering of the toe), and to bias the foot in dorsiflexion (or raising the toe). The ankle joint has a rear pivot rearward of a hydraulic link for a smooth feel. The ankle joint has an internal bumper in a hydraulic cylinder for a smooth feel. The ankle joint has an internal hydraulic compensator disposed in the cylinder and carried by the piston to equalize volume.

Abstract: A prosthetic device including an upper member having an upper end and a lower end, a wave member having a toe end and a heel end, and a third member having a proximal end and a distal end. In the preferred prosthetic device, the toe end of the wave member is fixedly attached to the upper member and the heel end of wave member is adapted to be deflected.

Abstract: An artificial foot and ankle joint consists of a curved leaf spring foot member having a heel extremity and a toe extremity, and a flexible elastic ankle member that connects the foot member for rotation at the ankle joint. An actuator motor applies torque to the ankle joint to orient the foot when it is not in contact with the support surface and to store energy in a catapult spring that is released along with the energy stored in the leaf spring to propel the wearer forward. A ribbon clutch prevents the foot member from rotating in one direction beyond a predetermined limit position. A controllable damper is employed to lock the ankle joint or to absorb mechanical energy as needed. The controller and sensing mechanisms control both the actuator motor and the controllable damper at different times during the walking cycle for level walking, stair ascent, and stair descent.

Abstract: Disclosed are passive lower limb prosthetic devices comprising at least a two degree of freedom mechanism and a network of compression springs.

Abstract: The present invention relates to an improved system for use in rehabilitation and/or physical therapy for the treatment of injury or disease to the lower limbs or extremities. The system can enable an amputee to proceed over any inclined or declined surface without overbalancing. The system is mechanically passive in that it does not utilize motors, force generating devices, batteries, or powered sources that may add undesirable weight or mass and that may require recharging. In particular the system is self-adapting to adjust the torque moment depending upon the motion, the extent of inclination, and the surface topography. An additional advantage of the improvement is that the system can be light and may also be simple to manufacture.

Abstract: An ankle-foot prosthesis includes a foot plate, an ankle frame attached to the foot plate, a yoke pivotally connected to the ankle frame and including a member for attaching to a leg, a damper having a first end connected to the yoke and a second end connected to the ankle frame, and a control mechanism for switching the damper between low and high settings.

Abstract: In a lower limb prosthesis an ankle unit has a combination of an hydraulic piston and cylinder assembly providing a continuously damped range of ankle flexion and a resilient telescopic shock absorber. The damping resistance of the piston and cylinder assembly is the predominant resistance to ankle flexion and is provided by a piston which is axially moveable in a cylinder centered on the shin axis. The wall of the cylinder has a cylindrical outer bearing surface for a sleeve which is translationally displaceable relative to the piston and cylinder assembly according to the axial load, the sleeve being resiliently mounted by a compression spring which extends axially within the sleeve and has an integral end portion forming an upper bulkhead of the cylinder. The sleeve is also rotatable on the cylinder wall, the spring providing torsional resistance.

Abstract: A method of making a resilient prosthetic/orthotic component, particularly a shank for a lower extremity prosthesis in which the shank includes multiple sections which are unbounded in one or more portions of each other, and wherein the shank sections incorporate at least one voids and inserted materials between one or more shank sections to enhance shank flexibility while reducing stresses which can cause premature failure.

Abstract: In one aspect, the invention provides methods and apparatus facilitating an adjustable-stiffness prosthesis or orthosis (including approximations to arbitrarily definable non-linear spring functions). Spring rates may be varied under no-load conditions during a walking gate cycle to minimize power consumption. In another aspect, the invention provides methods and apparatus for outputting positive power from a prosthesis or orthosis, facilitating high-performance artificial limbs. In one embodiment of the invention, the positive power is transferred from a functioning muscle to the prosthesis or orthosis, which mimics or assists a non-functioning or impaired muscle. In another embodiment of the invention, the positive power comes from an on-board power source in the prosthesis or orthosis.

Abstract: The present invention relates to an improved system for use in rehabilitation and/or physical therapy for the treatment of injury or disease to the lower limbs or extremities. The system can enable an amputee to proceed over any inclined or declined surface without overbalancing. The system is mechanically passive in that it does not utilize motors, force generating devices, batteries, or powered sources that may add undesirable weight or mass and that may require recharging. In particular the system is self-adapting to adjust the torque moment depending upon the motion, the extent of inclination, and the surface topography. An additional advantage of the improvement is that the system can be light and may also be simple to manufacture.

Abstract: The present invention provides divided-end artificial limbs and methods for making divided-end artificial limbs that are inexpensive, simple, and customizable. A limb is formed by dividing an end of an elongated shaft member into extending prongs that are shaped into custom lengths and curvatures. Furthermore, the method of the present invention provides affixing a sole plate to the limb, reinforcement of the prongs by nesting additional prongs within the elongated shaft member, dividing the proximal end of the shaft member into circumferentially spaced-apart fingers, and dividing a midsection of the shaft member into circumferentially spaced-apart flexing vanes. The present invention also provides that the prongs may be further modified by division into toe and heel extensions or by wrapping a prong around another prong to form a sole. Methods of reducing stress concentration using bolts and stress relief holes in these limbs are also presented.

Abstract: A prosthetic limb has an outer surface that is a mirror image of an intact limb or a generic limb design. The intact limb is scanned and the surface data is manipulated to create a virtual mirror image. If generic data is used, the intact leg can be measured and the generic surface can be adjusted so the prosthetic limb appears similar to the intact limb. The end of the amputated limb is also measured to obtain socket data. A knee and foot are incorporated to form a virtual prosthetic limb represented by design data. The design data for the virtual prosthetic limb is forwarded to a rapid prototyping machine that fabricates the entire leg simultaneously. Once completed, the prosthetic limb is shipped to the patient.

Abstract: The present invention relates to an improved system for use in rehabilitation and/or physical therapy for the treatment of injury or disease to the lower limbs or extremities. The system can enable an amputee to proceed over any inclined or declined surface without overbalancing. The system is mechanically passive in that it does not utilize motors, force generating devices, batteries, or powered sources that may add undesirable weight or mass and that may require recharging. In particular the system is self-adapting to adjust the torque moment depending upon the motion, the extent of inclination, and the surface topography. An additional advantage of the improvement is that the system can be light and may also be simple to manufacture.

Abstract: A stable shock absorbing prosthetic foot that transfers energy between heel strike and toe-off. A toe plate is separated from one or more other plates by a bumper assembly located at each of the toe end and heel end of the foot. Certain embodiments of the shock absorbing foot of the present invention are designed for use with a prosthetic ankle. A torsion adapter may also be used to attach a prosthetic foot of the present invention to the remainder of a prosthesis.

Abstract: An articulating connection or joint for a limb support device having a first support member and a second support member pivotably couples together the first support member and the second support member. The articulating connection can include one or more first articulating connection member, or load-bearing pin, and one or more second articulating connection member, or bushing, disposed about the first and second support members. The load-bearing pin is coupled to one of the support members and the bushing is coupled to another of the support members. The bushing is configured to rotatingly receive the load-bearing pin and interacts with an actuation member configured to apply a force on the load-bearing pin to eccentrically align the load-bearing pin relative to the bushing so that the load-bearing pin continuously follows and contacts a bearing surface of the bushing during use of the limb support device, thereby inhibiting noise generation from the interaction of the bushing and load-bearing pin.

Abstract: A prosthetic foot and lower part of leg has a semi-rigid, resilient foot keel extending in a longitudinal direction and a semi-rigid, resilient leg portion attached at a lower end to the foot keel. The leg portion includes a plurality of resilient leaf spring type members which are spaced apart in the sagittal plane intermediate their upper and lower ends and which are coupled together at their upper and lower end portions. The members are anterior facing convexly curved at their lower ends forming an ankle joint area and extend upwardly above in a substantially anterior facing convexly curve to a substantially vertically oriented upper end which is displaced substantially in the longitudinal direction in amputee gait for improved dynamic response.

Abstract: The prosthetic foot (1) consists of three or four laminas, a lower lamina (1a) defining the under-heel and the foot front, a rear lamina (1b) defining the heel and functioning as the Achilles tendon and as the soleus muscle, two upper laminas (1c and 1d) defining the front part of the foot and performing the function of the front tibial muscle, and a connector (2) in proximity to the ankle to serve as a coupling for a tube (3).

Abstract: A keel for a prosthetic foot comprises a unitary keel body having a longitudinal axis and a length L. The keel body includes a forefoot portion, a heel portion, and an ankle portion extending therebetween. In addition, the keel comprises a first bumper disposed in a first capture cavity in the ankle portion. The first bumper has a central axis that is substantially perpendicular to the longitudinal axis of the keel body in top view.

Abstract: A resilient lower extremity prosthesis comprising a foot, an ankle and a shank above the ankle is provided with an artificial muscle on the shank of the prosthesis for storing energy during force loading of the prosthesis in the active propulsion phase of a person's gait and in the later stages of stance-phase of gait releasing the stored energy to aid propulsion of the person's trailing limb and body.

Abstract: The present foot prosthesis includes various structural features that provide the foot with advantageous rollover properties. In certain embodiments, the foot guides rollover toward the medial side. For example, an asymmetrical upper element and a correspondingly shaped resilient ankle member support more of the wearer's weight on the lateral side as the foot rolls over. In another embodiment, stiffeners added to the resilient ankle member increase the stiffness on the lateral side relative to the medial side. In certain other embodiments, the foot provides progressively increasing support from mid stance through toe off. For example, a gap between the resilient ankle member and the lower element closes during the later portion of the wearer's gait. The closing gap increases a contact area between the resilient ankle member and the lower element, providing progressively increasing support. In another embodiment, the foot includes a gap between a lower front edge of an attachment adapter and the upper element.

Abstract: The present foot prosthesis includes various structural features that provide the foot with advantageous rollover properties. In certain embodiments, the foot guides rollover toward the medial side. For example, an asymmetrical upper element and a correspondingly shaped resilient ankle member support more of the wearer's weight on the lateral side as the foot rolls over. In another embodiment, stiffeners added to the resilient ankle member increase the stiffness on the lateral side relative to the medial side. In certain other embodiments, the foot provides progressively increasing support from mid stance through toe off. For example, a gap between the resilient ankle member and the lower element closes during the later portion of the wearer's gait. The closing gap increases a contact area between the resilient ankle member and the lower element, providing progressively increasing support. In another embodiment, the foot includes a gap between a lower front edge of an attachment adapter and the upper element.

Abstract: A prosthetic foot (100) incorporates a foot keel (101) and a resilient calf shank (105) with its lower end connection to the foot keel to form an ankle joint of the prosthetic foot. The foot keel has forefoot and hindfoot portions and a midfoot portion extending between the forefoot and hindfoot portions. The calf shank extends upward from the foot keel by way of an anterior facing convexly curved portion (106) of the shank, and is secured to the foot keel by way of a coupling element (107) which is monolithically formed with the forefoot portion of the foot. The lower end of the shank is reversely curved (110) and housed by a reversely curved portion (112) of the coupling element.

Abstract: A simple, inexpensive prosthetic foot is provided incorporating a cushioned ankle including an ankle block formed of a resilient material or bladder having desired compliance and energy return characteristics. The ankle block is sandwiched between a foot element and an ankle element. One or more openings extends through the ankle block with a substantially transverse orientation relative to a forward walking motion. The size and shape of these openings, as well as the insertion of different types of stiffeners therein, provide desired performance characteristics to the ankle block. When the ankle block takes the form of one or more inflatable bladders, the pressure within these bladders is individually controlled by valves to provide desired performance characteristics to different portions of the prosthetic foot. A pump system can also be used to control and generate fluid pressure into these bladders.

Abstract: The present foot prosthesis includes various structural features that provide the foot with advantageous rollover properties. In certain embodiments, the foot guides rollover toward the medial side. For example, an asymmetrical upper element and a correspondingly shaped resilient ankle member support more of the wearer's weight on the lateral side as the foot rolls over. In another embodiment, stiffeners added to the resilient ankle member increase the stiffness on the lateral side relative to the medial side. In certain other embodiments, the foot provides progressively increasing support from mid stance through toe off. For example, a gap between the resilient ankle member and the lower element closes during the later portion of the wearer's gait. The closing gap increases a contact area between the resilient ankle member and the lower element, providing progressively increasing support. In another embodiment, the foot includes a gap between a lower front edge of an attachment adapter and the upper element.

Abstract: The invention provides a prosthetic foot device including an elongated upper forefoot portion extending through an upper attachment section, forwardly through an arch section, and to a toe section positioned at a toe location of a natural foot. The foot device also includes an elongated lower forefoot portion extending through an upper attachment section attached to the attachment section of the upper forefoot portion, and forwardly under the arch section of the upper forefoot portion to a terminal end positioned under the ball location of a natural foot and rearward of the toe section of the upper forefoot portion.

Abstract: An ultrasound treatment system in accordance with the present invention comprises an ultrasonic transducer, a handpiece, a probe, a sheath, a clamping member, an operation unit, an operating member, a suction base, and a perfusion base. The ultrasonic transducer generates ultrasonic vibrations. The handpiece has the ultrasonic transducer incorporated therein and serves as an operation unit. The probe is connected to the ultrasonic transducer, and serves as a vibration transmitting member for transmitting ultrasonic vibrations to a distal member realizing a stationary portion that is a treatment portion for treating a living tissue. The sheath serves as a protecting member for shielding the probe. The clamping member is opposed to the distal member at the distal end of the sheath, and realizes a movable portion that is another treatment portion for clamping a living tissue in cooperation with the distal member.

Abstract: A prosthetic foot incorporate a foot keel and a calf shank connected to the foot keel to form an ankle joint area of the prosthetic foot. The foot keel has forefoot and hindfoot portions and a relatively long midfoot portion extending between and upwardly arched from the forefoot and midfoot portions. The calf shank includes a downward convexly curved lower end which is attached at a portion thereof to the keel midfoot portion by way of an adjustable fastener arrangement. The foot has biplanar motion capability and, in a preferred form, also has high low dynamic response characteristics. The adjustable fastener arrangement permits adjustment of the alignment of the calf shank and the foot keel with respect to one another in the longitudinal direction of the foot keel for tuning the performance of the prosthetic foot.

Abstract: A prosthetic foot device with variable stiffness response includes a variable energy transfer mechanism disposed between first and second foot members to transfer a variable amount of energy between the members during use. A chamber is associated with one of the first and second foot members, and a piston is associated with another of the first and second foot members and is movable in the chamber. At least one aperture is formed between the piston and the chamber. A variable viscosity fluid is disposed in the chamber and displaceable through the at least one aperture between the piston and the chamber to allow fluid to flow within the chamber between opposite sides of the piston. The variable viscosity fluid has a viscosity that is variable to vary an ability of the variable viscosity fluid to flow through the at least one aperture.