Abstract:
An alpine ski binding system for releasably securing a ski boot to a ski. The binding system includes a secondary toe release that provides an attenuated release threshold under lateral shear loading conditions that can cause anterior cruciate ligament injuries. The secondary toe release responds to a trigger that senses the lateral shear loads applied to the inside (medial) afterbody of the ski and triggers the secondary toe release the boot at an attenuated release torque. Lateral shear loads applied to the ski along the leading (medial) forebody and along the entire outside (lateral side) of the ski substantially do not cause the trigger to trip.

Description:
RELATED APPLICATION DATA  
       [0001]     This application claims the benefit of priority of U.S. Provisional Patent Application Ser. No. 60/836,454, filed Aug. 8, 2006, and titled “Knee-Friendly Ski Binding,” which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention generally relates to the field of alpine ski bindings. In particular, the present invention is directed to an alpine ski binding system having release logic for inhibiting anterior cruciate ligament injury.  
       BACKGROUND  
       [0003]     Sprains and other injuries of the anterior cruciate ligament (ACL) of the human knee are painful, debilitating, and expensive and time consuming to repair and rehabilitate. In skiing, the incidence of ACL injury began to rise in the late 1970s to become the sport&#39;s most common serious injury by the late 1980s. Since the early to mid 1990s the risk of sustaining this injury has stabilized and then declined modestly. However, at 15% to 20% of all ski-related injuries, it still remains the most common injury, with more than 20,000 per year in the U.S. alone. From 1983 on, changes in the incidence of ACL injury have been tracked by a series of “Trends” papers published as Special Technical Publications (STPs) by the American Society for Testing and Materials (ASTM).  
         [0004]     In October, 1995, the American Journal of Sports Medicine published a paper titled “A Method To Help Reduce The Risk Of Serious Knee Sprains Incurred In Alpine Skiing.” The paper documented the results of a training program for on-slope ski-area employees at 20 ski areas in the U.S. and compared injury rates for the group with both a historical control group (the same ski areas for the two prior seasons) and an ad hoc control group of 20 ski areas that had not yet joined the training regime. The training involved a highly structured, video-based discussion format. Actual footage of ACL injuries was used to create a kinesthetic awareness of the events leading to the most common types of ACL injury. The program reported a 62% reduction in ACL injuries overall, and for ski patrollers, the highest risk subgroup, the reduction was 76%. This program identified the “phantom foot” scenario as the most likely mechanism of ACL injury. In this scenario the skier is off-balance to the rear with most of the weight on the downhill (outside) ski.  
         [0005]     In later studies published in ASTM STPs, it was shown that the equipment associated with ACL injuries was comparable in quality and overall release performance to the equipment of the general population at risk but superior in every quality to equipment associated with sprains and fractures below the knee. These studies show that contemporary ski bindings, regardless of their condition, are not capable of reducing the risk of ACL injuries.  
       SUMMARY OF THE DISCLOSURE  
       [0006]     One aspect of the present invention is a ski binding configured to be secured to a snow ski and selectively retain a ski boot having a heel and a toe and worn by a skier having a tibial axis, the snow ski having a first-quadrant edge, a second-quadrant edge, a third-quadrant edge, a fourth-quadrant edge and a trailing end, the ski binding comprising: a heel piece for releasably engaging the heel of the ski boot; a toe piece for releasably engaging the toe of the ski boot, wherein the toe piece and the heel piece provide the ski binding with a non-attenuated release torque about the tibial axis of the skier when: the ski binding is mounted to the snow ski; the skier is wearing the ski boot; and the ski boot is properly captured in the ski binding; and release logic providing the ski binding with an attenuated release torque about the tibial axis in response substantially only to a lateral shear force being applied to the snow ski at a location along the third-quadrant edge.  
         [0007]     Another aspect of the present invention is a ski binding system configured to be secured to a snow ski and selectively retain a ski boot having a heel and a toe and worn by a skier having a tibial axis, the snow ski having a first-quadrant, a second-quadrant, a third-quadrant, a fourth-quadrant and a trailing end, the ski binding system comprising: an attenuated release logic mechanism for being secured to the snow ski and being configured to fixedly receive a heel piece and a toe piece, the attenuated logic mechanism including: a secondary toe release for providing, when the ski binding system is secured to the snow ski, the heel and toe pieces are fixedly secured to the attenuated release logic mechanism, and the ski boot is properly engaged between the heel and toe pieces: an attenuated release in response to lateral shear loads applied to the snow ski in the third-quadrant of the snow ski; and a non-attenuated release in response to lateral shear forces applied to the snow ski in the fourth-quadrant of the snow ski; a trigger operatively configured, when the ski binding system is secured to the snow ski, to trigger the secondary toe release to switch from the non-attenuated release to the attenuated release in responses to a triggering third-quadrant shear force.  
         [0008]     Still another aspect of the present invention is a method of releasing a ski boot from an alpine ski binding system, comprising: sensing lateral shear forces applied to a snow ski having a first-quadrant, a second-quadrant, a third-quadrant and a fourth-quadrant; determining when a virtual net shear force present in the third-quadrant exceeds a threshold value; in response to the net virtual shear force applied to the snow ski in the third-quadrant exceeds the threshold value, triggering a secondary toe release; and releasing via the secondary toe release the ski boot from the binding system. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:  
         [0010]      FIG. 1  is a partial top view of a conventional left-leg ski illustrating conventions used in the present disclosure;  
         [0011]      FIG. 2  is a graph of a theoretical release envelope, as seen relative to the tibial axis of a skier&#39;s leg, illustrating release/retention characteristics typical of a contemporary conventional ski binding having a binding pivot point located between the heel piece and the tibial axis of the skier&#39;s leg;  
         [0012]      FIG. 3  is a graph of a theoretical release envelope, as seen relative to the tibial axis of a skier&#39;s leg, illustrating release/retention characteristics typical of a contemporary conventional ski binding having a binding pivot point located between the tibial axis of the skier&#39;s leg and the toe of the ski boot;  
         [0013]      FIG. 4  is a graph of a theoretical release envelope, as seen relative to the tibial axis of a skier&#39;s leg, illustrating release/retention characteristics typical of a contemporary conventional ski binding having a binding pivot point located forward of the toe of the ski boot;  
         [0014]      FIG. 5  is graph of a theoretical release envelope, as seen relative to the tibial axis of a skier&#39;s leg, illustrating release/retention characteristics typical of a ski binding system having a third-quadrant attenuated secondary toe release;  
         [0015]      FIG. 6  is a top view/diagrammatic view of an exemplary ski system having the theoretical release envelope of  FIG. 5 ;  
         [0016]      FIG. 7  is a graph of the release threshold for the secondary release mode of the binding system of  FIG. 6 ;  
         [0017]      FIG. 8  is a graph of the attenuation factor for the secondary release torque and trigger platform trip torque for the binding system of  FIG. 6 ;  
         [0018]      FIG. 9A  is an isometric partial top view of a ski system that includes a third-quadrant release-logic mechanism of the present disclosure mounted to a left-leg ski, showing the mechanism in an unreleased state;  FIG. 9B  is an isometric partial top view (rotated 180° relative to  FIG. 9A ) of the third-quadrant release-logic mechanism of  FIG. 9A  with the boot sole and the heel and toe pieces removed for clarity;  
         [0019]      FIG. 10A  is an isometric partial top view of the ski system of  FIG. 9A  showing the third-quadrant release-logic mechanism in a released state;  FIG. 10B  is an isometric partial top view (rotated 180° relative to  FIG. 10A ) of the third-quadrant release-logic mechanism of  FIG. 10A  with the boot sole and the heel and toe pieces removed for clarity;  
         [0020]      FIG. 11  is an enlarged plan view of the ski system of  FIGS. 9A-10B  showing the upper surface of the ski and the trigger platform (and the secondary toe release) removed and placed upside-down next to the ski so as to illustrate exemplary components that may be used to make the third-quadrant release-logic mechanism work;  
         [0021]      FIG. 12  is an isometric partial top view of a second embodiment of a ski system that includes a third-quadrant release-logic mechanism of the present disclosure mounted to a right-leg ski, showing the mechanism in an unreleased state;  
         [0022]      FIG. 13  is an isometric partial top view of a second embodiment of the ski system of  FIG. 12  showing the third-quadrant release-logic mechanism in a released state;  
         [0023]      FIG. 14  is an isometric exploded partial view of a second embodiment of the ski system of  FIGS. 12 and 13  showing the various components of the system;  
         [0024]      FIG. 15  is a bottom view of a second embodiment of the third-quadrant release-logic mechanism of  FIG. 12  with bottom plates removed to illustrate the state of components of the mechanism when the mechanism is in its unreleased state;  
         [0025]      FIG. 16  is a bottom view of a second embodiment of the third-quadrant release-logic mechanism of  FIG. 13  with bottom plates removed to illustrate the state of components of the mechanism when the mechanism is in its released state;  
         [0026]      FIG. 17  is an isometric top view of a boot sole and a dual-release-threshold toe assembly that can be substituted for the secondary to release mechanisms of  FIGS. 3A-5  and  FIGS. 12-16 , respectively;  
         [0027]      FIG. 18  is an isometric bottom view of the base of the toe assembly of  FIG. 17  showing the actuator in its unreleased position;  
         [0028]      FIG. 19  is an isometric bottom view of the base of the toe assembly of  FIG. 17  showing the actuator in a released position;  
         [0029]      FIG. 20  is an isometric top view of the toe assembly showing the housing, toe retainer and toe retainer studs removed, illustrating the unreleased state of the toe assembly;  
         [0030]      FIG. 21  is an isometric top view of the toe assembly showing the housing, toe retainer and toe retainer studs removed, illustrating the unreleased state of the toe assembly;  
         [0031]      FIG. 22  is an isometric partial top view of a ski system that includes an electronic third-quadrant release-logic binding system;  
         [0032]      FIG. 23  is an isometric bottom view of the electronic third-quadrant release-logic binding system of  FIG. 22 ; and  
         [0033]      FIG. 24  is a partial top view/cross-sectional view/diagrammatic view of the electronic third-quadrant release-logic binding system of  FIGS. 22 and 23  illustrating the operation of the binding. 
     
    
     DETAILED DESCRIPTION  
       [0034]     The present disclosure is directed to an alpine ski binding system having release logic configured to have an attenuated release torque when a shear force is applied to the medial side of the ski, rearward of the tibial axis of the leg of a skier. As discussed below, this region is denoted for convenience “quadrant 3,” “Q3,” “third quadrant,” or a like term. During skiing maneuvers there are many lateral shear forces acting simultaneously along the physical edge of the ski as well as inertial forces between the various masses of the skier and his equipment that generate lateral shear forces between the boot and binding. All these lateral shear forces can be resolved to one virtual force at one location along a virtual, infinitely long, ski plus a couple (pure torque). In the discussion below any references to “shear force” are meant to describe this virtual force acting on a virtual ski. As mentioned in the Background section above, it is believed that certain third-quadrant loadings, when applied to skiers&#39; legs via current generation bindings, are frequently implicated in injuries to the skiers&#39; anterior cruciate ligaments (ACLs). The studies cited in the Background section above, careful analysis of video footage of skiers as ACL injuries occurred, tests of contemporary release bindings, results of skier strength in near ACL postures and measurements of the loads applied to a ski during actual skiing maneuvers have led the present inventors to develop a computer model for a ski binding with selective release characteristics and working prototypes of several examples of the underlying principles of the present disclosure, which are discussed below. The computer model uses a coordinate system based on FIG. X 1 . 4  of the Appendix to ASTM Test Method F504 and creates a partial release envelope as described in that Appendix. (ASTM Test Method F504 and its Appendix are incorporated herein by reference in their entireties.) Using the computer model, the present inventors can shape the release envelope to accommodate the retention requirements of skiers so that a narrow but predictable margin of retention is provided in the area of the envelope associated with the most common mechanism of ACL injury.  
         [0035]     An alpine ski binding system of the present disclosure provides a reduced retention in areas of the release envelope that may influence ACL injury. Such a binding system creates a depression in the portion of the release envelope most likely to be associated with ACL injury. The location of the depression and the magnitude of its effect are adjustable, as described in more detail below. To the best of the present inventors&#39; knowledge, no one has yet devised a binding having release logic designed to provide a reduced release threshold (relative to contemporary conventional bindings that have a fixed release threshold regardless of the location of the shear load on the ski) only when the net shear force on the ski resolves to a load in the third quadrant. With such a reduced third-quadrant release threshold, a binding made in accordance with the present disclosure can advantageously release before a skier&#39;s ACL is put at risk of injury. As seen below, such release threshold logic may be implemented in a number of ways using various mechanisms and/or electronics. In addition, with these mechanisms and/or electronics, the release envelope for third-quadrant loadings can be shaped to accommodate the retention requirements of skiers so that a narrow but predictable margin of retention is provided in the area of the envelope associated with the most common mechanism of ACL injury. However, prior to describing several ski binding systems that include unique release-threshold logic, it is beneficial to understand the release-threshold profile of most current ski bindings.  
         [0036]     Referring now to  FIG. 1 , this figure illustrates a naming convention used throughout the following disclosure and in the appended claims.  FIG. 1  shows a ski system  100  that includes a left ski  104  having a boot region  108  that receives a ski boot (not shown) during use of the ski. The dark boot region  108  represents the area of ski  104  confronted or overlain by the sole of the ski boot when the boot is properly engaged in a binding (not shown) affixed to the ski. In this figure, the tail end of ski  104  is located out of the view of the figure to the left along longitudinal central axis  112  of the ski, and the leading tip of the ski is located out of the view of the figure and to the right along longitudinal central axis  112 . It should be noted that quadrants  1  and  2  extend to infinity beyond the tip of the ski and quadrants  3  and  4  extend to infinity beyond the tail of the ski. While not shown, those skilled in the art can readily envision the heel and toe pieces of a conventional alpine binding being generally located, respectively, to the immediate left and right of boot region  108 . The location of the longitudinal central axis of a skier&#39;s tibia bone (i.e., tibial axis) along ski  104  is represented by dashed line  116 .  
         [0037]     For convenience, left ski  104  is parsed into four shear loading quadrants, i.e., quadrants  1  through  4 , with tibial axis  116  and longitudinal central axis  112  demarcating the differing quadrants. Each net resolved lateral shear force (or “virtual” force) (Fy) applied in a corresponding quadrant  120 ,  124 ,  128 ,  132  of ski  104  and the corresponding moment (Mz) this force causes at tibial axis  116  are related by the basic equation, Force times Distance equals Torque. Here, the Force is the net resolved lateral shear force Fy, the Distance is the distance of shear force Fy from tibia axis  116  and the Torque is the tibial moment Mz.  
         [0038]     Forces on ski  104  during skiing in each quadrant  1 - 4  produce a unique combination of force Fy and moment Mz at tibial axis  116 , i.e., on the leg of the skier. A ski binding system made in accordance with the present invention is designed to recognize when loads on a ski are in quadrant  3  and respond by enabling release of the ski binding at a lower than normal release torque, as represented here as tibial moment Mz. In the following  FIGS. 2-5 ,  7  and  8 , the twisting moment Mz on the leg is expressed in terms of “(%) of Recommended,” as defined by section 5 of ASTM standard F939, “Selection of Release Torque Values for Alpine Ski Bindings,” which is incorporated herein by reference in relevant part. While only the left ski  104  of a pair of skis is shown, it will be readily appreciated that for consistency of the noted convention, the convention for the right ski (not shown) would be a mirror image of the convention shown for the left ski about a line (not shown) parallel to longitudinal central axis  112  and spaced from the left ski. That is, quadrants  1  and  4  would be located on the outside (lateral side) of the right ski when worn by a skier, and quadrants  2  and  3  would be located on the inside (medial side) of the right ski.  
         [0039]      FIG. 2  is a graph  200  of a release envelope  204 A-B, as seen by a skier&#39;s leg, of a conventional “toe release” type alpine ski binding having a binding pivot point at the center of the radius of the heel piece, here 6.6 cm behind the tibial axis of the skier. Again, graph  200  is of the type shown in ASTM F504, FIG. X 1 . 4  and relates torque (Mz of  FIG. 1 ) about the reference axis of the leg (here, tibial axis  116  of  FIG. 1 ) at release to the position of the single force (Fy of  FIG. 1 ) on the ski that creates that torque. The “Position” (i.e., the horizontal axis  208 ) in  FIG. 2 , and in  FIGS. 2-5 ,  7  and  8 , refers to the virtual position of the single force Fy on an infinitely long ski that replaces all loads on the finite ski and produces the moment Mz. Here, position is measured from the tibial axis of the skier&#39;s leg. In the graph  200  of  FIG. 2 , as well as in the graphs  300 ,  400 ,  600  of  FIGS. 3, 4  and  6 , respectively, virtual “position” is plotted from (−)200 cm to +200 cm from the tibial axis, which is located at “0” on the horizontal axes of the corresponding respective graphs. Changes in the tibial moment Mz beyond these distances along the virtual ski are small in comparison to changes within these distances. The relationship of this virtual ski to an actual typical ski can be seen by the representation  212  of a ski placed in proper relation to the tibial axis, with the tail and tip of the ski being indicated by vertical lines  216 ,  220 , respectively.  
         [0040]     In conventional binding designs, the release envelope of the ski binding about the binding&#39;s pivot axis, which in the example is at the center of the heel radius  6 . 6  cm behind the tibial axis, is symmetrical in all four quadrants Q 1 -Q 4 . However, as seen in  FIG. 2  the release torque on the skier&#39;s leg as indicated by release envelope portion  204 A is much higher for loads applied to the after body of the ski than release envelope portion  204 B for loads applied to the fore body of the ski. The reason for this difference is the offset (here, 6.6. cm) in the location of the binding pivot axis from the location of the tibial axis. That said, it is readily seen from after-body release envelope portion  204 A that the release envelope is symmetrical for loadings in quadrants Q 3  and Q 4  and from fore-body release envelope  204 B that the release envelope is symmetrical for loadings in quadrants Q 1  and Q 2 .  
         [0041]     Whereas  FIG. 2  shows graph  200  for a conventional toe release type ski binding,  FIGS. 3 and 4  illustrate graphs  300 ,  400 , respectively, for two contemporary heel release type ski bindings. In  FIG. 3 , the binding has a pivot axis located forward of the tibial axis (“0” on the horizontal axis of graph  300 ) but behind the boot toe, and in  FIG. 4 , the binding has a pivot axis located forward of the boot toe. As seen from each of envelopes  304 A-B ( FIG. 3 ) and  404 A-B, the release torques on the leg are symmetrical for after body loadings in quadrants Q 3  and Q 4  and for fore body loadings in quadrants Q 1  and Q 2 . In each of the examples of  FIGS. 2-4 , the binding senses the same torque at release with respect to its own pivot axis, while the skier&#39;s leg, which has a different reference axis, senses a release torque that is dependent on the position of the load on the ski. It is noted that the foregoing analyses ignore the effects of friction and combined loading that may influence individual bindings in actual skiing.  
         [0042]     Each of the above graphs  200 ,  300 ,  400  of  FIGS. 2-4 , respectively, demonstrates a different problem. The toe release type binding of  FIG. 2  fails to sense the true load on the skier&#39;s leg in quadrant Q 3 . The heel release type binding of  FIG. 3  fails to sense the true load on the skier&#39;s leg in quadrant Q 1  and Q 2 . Although the binding of  FIG. 3  does lower the release threshold in quadrant Q 3 , it does not lower it sufficiently near the tail of the ski, which is the area of greatest risk to the ACL. The other heel release type binding of  FIG. 4  demonstrates the same problems as the binding of  FIG. 3 . Although it does lower the release threshold in quadrant Q 3  more than the binding of  FIG. 3 , the improvement is insufficient. Bindings of this type also lack an adequate margin of retention in response to loads applied to the after body of the ski near the tibial axis.  
         [0043]     In contrast to graphs  200 ,  300 ,  400  of  FIGS. 2-4 , respectively,  FIG. 5  contains a graph  500  illustrating a release envelope  504 A-D achievable using a ski system made in accordance with the present invention. As seen in  FIG. 5 , the ski system is able to distinguish loads applied in quadrant Q 3  and provide an attenuated release (represented by release envelope portion  504 C) relative to the non-attenuated release (represented by release envelop  504 A) relative to loads applied in quadrant Q 4 . As is readily seen by comparing graph  500  to graph  200  of  FIG. 2  for a conventional toe release type binding, it is seen that release envelope portions  504 A-B are nearly identical to release envelope  204 A-B of  FIG. 2 . In this case, this is so because graph  500  of  FIG. 5  is based on a ski system that utilizes the conventional toe release type binding of graph  200  of  FIG. 2 . However, it is seen from  FIG. 5  that augmentations made to such a conventional binding in the exemplary ski system used to generate graph  500  provide the ski system with an attenuated release envelope portion  504 C for loads in quadrant Q 3 , which appears to be the quadrant most implicated in ACL injury. Release envelope portion  504 D for a small portion of quadrant Q 1  is an artifact of the configuration of the particular ski system used to generate graph  500 .  FIG. 6  illustrates an alpine ski system  600  that can be used to achieve release envelope  504 A-D of  FIG. 5 .  
         [0044]     Referring now to  FIG. 6 , and also to  FIG. 5 ,  FIG. 6  shows ski system  600  as including a ski  604  and a binding system  608 . Binding system  608  includes, in this example, a pivotable secondary toe release  612  pivotable about a pivot axis  616  and a pivotable trigger, here a trigger platform  620 , pivotable about a pivot axis  624 . Binding system  608  also includes a toe release type boot binding  628  that includes a heel piece  632  and a toe piece  636  and has a binding pivot axis  640  close to the heel piece. Not shown, but readily envisioned as being captured between heel and toe pieces  632 ,  636 , is a ski boot, which may be a conventional ski boot. Also shown for context is the location of the tibial axis  644  of a skier when ski system  600  is properly secured to the skier&#39;s boot. Graph  500  of  FIG. 5  was created using ski system  600  as a model and using the particular input and calculated values shown in the following table.  
                                             Input Values for Example Calculations                                Ski Length   175.0   cm       Ski Tip length   14.0   cm       Ski Tail Length   5.0   cm       Boot Length   30.3   cm       Boot Heel to Binding   3.5   cm (+ forward − rearward)       Pivot       Boot Heel to Tibial Axis   10.1   cm (+ forward − rearward)       Boot Toe to Plate pivot   7.5   cm (+ forward − rearward)       Release Torque   100   % of recommended release torque       Plate Trip Torque   80   % of recommended release torque       Release Attenuation   50   % of recommended release torque                   From       Calculated Values:   tibial axis               Tail   72.9   cm       End of running surface   −67.9   cm       Mid running surface   10.1   cm       Boot Heel   −10.1   cm       Boot Toe   20.2   cm       Binding pivot   −6.6   cm       Tibial axis   0.0   cm       Plate pivot   27.7   cm       Start of surface   88.1   cm       Tip   102.1   cm                  
 
         [0045]     In ski system  600  of  FIG. 6 , distinguishing quadrant Q 3  loads is accomplished by isolating the boot and binding  628  from ski  604  by means of trigger platform  620  that pivots about pivot axis  624  forward of tibial axis  644 . In this example, pivot axis  624  of trigger platform  620  is also located forward of the toe of the ski boot. The performance of binding system  608  is controlled by a number of factors, including the location of the trigger platform pivot axis  624 , the location of the binding pivot axis  640 , the nominal release torque setting, the trigger platform trip torque setting, and the release attenuation setting. Until trigger platform  620  senses the trip torque specified in the table above, binding  628  functions in its primary release mode. However, once the specified trip torque is reached, trigger platform  620  enables an attenuated release when the torque specified in Table 1 is reached ( FIG. 5 ). Therefore the logic for a secondary release of the present invention requires two criteria to be met before release can take place. For ACL protection, this capability is limited to quadrant Q 3 . Although a small effect is created in quadrant Q 1  (as represented by release envelope portion  504 D of  FIG. 5 ), it does not cause a retention problem and may in fact reduce excess retention.  
         [0046]     The example graph  500  shown in  FIG. 5  describes a complex release threshold for quadrant Q 3  with a 50% attenuation in torque sensed by the leg at release over the full length of the after body of the finite ski  604  ( FIG. 6 ). Beyond that point the complex load on the leg simplifies and approaches a pure couple, a load not associated with the principle mechanism of ACL injury. Therefore, in the example of  FIG. 5 , the release threshold is programmed to go asymptotic to the 80% grid line as it approaches infinity (a pure couple).  
         [0047]      FIG. 7  is a graph  700  illustrating the secondary release threshold  704  (solid line) provided by ski binding system  608  of  FIG. 6 , i.e., the torque sensed by the skier&#39;s leg for loads in quadrant Q 3  when the trip torque and attenuated release torque criteria are met. As seen, the secondary release threshold  704  follows a portion of the trip torque profile  708  of trigger platform  620  and a portion of the attenuated release torque profile  712  of secondary toe release  612  ( FIG. 6 ). Graph  700  demonstrates how binding system  608  makes use of portions of both the heel release type binding of  FIG. 4  and the toe release type binding of  FIG. 2  in its logic for a secondary release in quadrant Q 3 .  FIG. 7  also shows that the release logic of binding system  608  calls for a series, not a parallel solution. This means that the criteria for both actuation of trigger platform  620  and attenuated release of secondary toe release  612  must be met for the attenuated release to take place.  
         [0048]      FIG. 8  is a graph  800  that introduces the concept of a retention threshold and various combinations of inputs of the table appearing above. A goal of the process of selecting the attenuated release torque threshold, the trigger platform trip torque, and the locations of the trigger platform and secondary toe release pivot axes  616 ,  624  is to provide the lowest practical secondary release threshold in areas of quadrant Q 3  associated with the greatest risk of ACL injury, while providing an appropriate margin of retention in all other areas of the quadrant. Line A in  FIG. 8  refers to the example solution shown in  FIGS. 5-7  and in the foregoing table, above. It is noted that line B may be a better compromise. Note that the threshold shown in this figure is for example only. As the requirements for retention in quadrant Q 3  are refined, changes will be required to the input values of the foregoing table of inputs and the resulting architecture of an ideal “knee-friendly” binding.  
         [0049]     As those skilled in the art will appreciate, the principles outlined above could also be used to modify the release threshold in other quadrants should the need arise.  
         [0050]     Whereas  FIGS. 5-8  address general concepts of the present invention, the following  FIGS. 9A-24  illustrate examples of binding system configurations that can be used to achieve the release logic that provides an attenuated release in response to substantially only loads applied in the third quadrant. Referring now to  FIGS. 9A-11 ,  FIG. 9A  illustrates an alpine ski system  900  made in accordance with the present invention. Ski system  900  includes a left ski  904  and a binding system  908  that includes a third-quadrant release-logic mechanism  912  and heel and toe pieces  916 ,  920 , respectively. In this example, heel and toe pieces  916 ,  920  are contemporary conventional heel and toe pieces available from manufacturers such as Tyrolia, Marker, Salomon, Atomic, Rossignol, etc. The selection of conventional heel and toe pieces for this example serves to clearly illustrate the general concept of the third-quadrant release logic (here provided by third-quadrant release-logic mechanism  912 ) and its relation to current conventional bindings that consist essentially only of heel and toe pieces  916 ,  920 . This selection also serves to illustrate that third-quadrant release-logic mechanism  912  could readily be sold as a retrofit component for conventional ski systems or otherwise separately from conventional skis and binding.  FIG. 9A  also illustrates, for the sake of context, a ski-boot sole  924  clamped into binding system  908  in a conventional manner between heel and toe pieces  916 ,  920 . Third-quadrant release-logic mechanism  912  is essentially configured to change the release-threshold envelope  204 A-B ( FIG. 2 ) for shear forces applied to ski  904  in the third quadrant.  
         [0051]     Referring now to  FIG. 9B , which is similar to  FIG. 9A  but shows ski system  900  without ski-boot sole  924  and heel and toe pieces  916 ,  920  for the sake of illustration,  FIG. 9B  shows two primary components of release-logic mechanism  912 , i.e., a trigger platform  932  and a secondary toe release  936 . Heel piece  916  ( FIG. 9A ) is fixedly secured to trigger platform  932 , and toe piece  920  is fixedly secured to secondary toe release  936 . As will be described below in detail, trigger platform  932  is pivotably secured to ski  904  at a pivot point  940  located forward (toward the tip of the ski) of the toe end of ski-boot sole  924  ( FIG. 9A ) and, since ski  904  is a left-leg ski, is secured to the ski so as to be pivotable relative to the ski only in a counterclockwise direction from the position shown in  FIG. 9B . For a right-foot ski (not shown), a comparable trigger platform would be secured to the right-foot ski so as to be pivotable only in a clockwise direction. In addition to being pivotable only in the counterclockwise direction, trigger platform  932  is constrainably pivotable in the counterclockwise direction such that a non-zero threshold shear force, which translates into a “trigger trip torque”, is needed in the third quadrant before the trigger platform begins to move appreciably and provide its triggering effect. One example of a trigger trip torque mechanism for providing this trigger threshold is an adjustable trip torque mechanism  1100 , described below in connection with  FIG. 11 . As discussed below, this trip torque is a function of the location of pivot point  940  relative to tibial axis  942 , as well as the setting of the trip torque mechanism. For the present discussion, however, it is necessary only to understand that trigger platform  932  is constrainably pivotable only in the counterclockwise direction. Otherwise, trigger platform  932  is secured to ski  904  so that substantially no movement occurs between these two components in a direction normal to the width of the ski.  
         [0052]     Secondary toe release  936  is secured to trigger platform  932  so as to be constrainably pivotable about a pivot point  944  located between the toe end of ski-boot sole  924  ( FIG. 9A ) and pivot point  940  of the trigger platform and to be pivotable substantially only in a clockwise direction relative to the trigger platform from the position shown in  FIG. 9B . Third-quadrant release-logic mechanism  912  also includes an attenuated release threshold mechanism, such as adjustable release threshold mechanism  1104  of  FIG. 11 , that provides secondary toe release  936  with a constrained pivoting action. The resistance torque of secondary toe release  936  caused by the secondary-release threshold mechanism is referred to herein as “attenuated release torque.” When trigger platform  932  is in a non-triggering position, such as shown in  FIG. 9B , secondary toe release  936  is held in the unreleased position shown in  FIG. 9B  by a triggerable latch mechanism, such as latch mechanism  948 . Latch mechanism  948  includes a latch  952  pivotably secured to trigger platform  932  at a pivot point  956 . Latch  952  includes an opening  960  ( FIG. 10B ) that receives a pin  964  ( FIG. 10B ), which is fixed relative to ski  904 . In the unreleased position of secondary toe release  936  shown, latch  952  engages a catch  968  that is fixed to the secondary toe release.  
         [0053]     When trigger platform  932  pivots counterclockwise relative to ski  904  in response, for example, to a threshold-exceeding torque in response to a shear force in the third quadrant (see  FIG. 1 ), latch  952  and its pivot point  956  (which is fixed relative to the trigger platform) move, thereby causing stationary pin  964  ( FIG. 10B ) to pivot the latch about its pivot point and cause the distal end  972  of the latch to move out of engagement with catch  968  on secondary toe release  936 . With distal end  972  of latch  952  out of the way, secondary toe release  936  is free to pivot in response to a torque exceeding the secondary release torque clockwise relative to trigger platform  932 , thereby releasing ski-boot sole  924  ( FIG. 9A ) from binding system  908  ( FIG. 9A ). If desired, secondary toe release  936  may be provided with a secondary catch  976  for engaging distal end  972  of latch  952  when third-quadrant release-logic mechanism  912  is in a released state so as to limit the pivoting of the secondary toe release. FIGS.  10 A-B each show third-quadrant release-logic mechanism  912  in a released state  1000 , with trigger platform  932  pivoted counterclockwise relative to ski  904 , latch  952  pivoted counterclockwise out of engagement with catch  968  and secondary toe release  936  pivoted clockwise relative to the trigger platform. Again, this released state  1000  is substantially only achieved from the unreleased state upon application of a shear force to the third-quadrant of ski  904  that exceeds both the trip plate trigger torque and the secondary toe release torque.  
         [0054]     Referring now to  FIG. 11 , it was mentioned above that trigger platform Q 332  is secured to ski  904  so as to be constrainably pivotable about pivot point  940 .  FIG. 11  illustrates examples of mechanisms that can be used to provide this type of securement. In this example, trigger platform  932  is fastened to ski  904  by a threaded fastener  1104  that threadedly engages a matching threaded opening  1108  in the ski. The engagement of fastener  1104  with trigger platform  932  and ski  904  is such that when the trigger platform is properly secured to the ski it is substantially freely pivotable about pivot point  940  but constrained from moving away from the upper surface  1110  of the ski. In other embodiments, a fastener other than a threaded fastener may be used. In addition, if desired, a torsion mechanism (not shown) or other pivot-constraining connection may be provided to provide a desired amount of resistance to pivoting.  
         [0055]     Trigger platform  932  is also held down by a sliding hold-down mechanism  1112  that, when the trigger platform is properly installed on ski  904 , allows the trigger platform to pivot about pivot point  940  but not substantially move away from upper surface  1110  of the ski. In this example, hold-down mechanism  1112  includes a slidable hold-down  1116  that is fixedly secured to ski  904 , for example, using a threaded fastener  1120 . Hold-down  1116  is movable within a generally T-shaped slot  1124  on trigger platform  932  that is preferably, but not necessarily, sized to limit the range of pivot of the trigger platform. The T-shape of slot  1124  generally conformally receives the combination of hold-down  1116  and fastener  1120  that largely forms a like T-shape. To reduce friction, ski  904  may be provided with a low-friction bearing plate  1128  and/or trigger platform  932  may be provided with one or more low-friction bearings  1132 .  
         [0056]     As mentioned, the resistance to pivoting of trigger platform  932  relative to ski  904  that provides the trigger platform with a trigger trip torque threshold is provided by adjustable trip torque mechanism  1100 . In this example, trip torque mechanism  1100  includes a fixed screw-guide bracket  1140  that is fixedly secured to ski  904 , for example, using a threaded fastener  1144 . Screw-guide bracket  1140  receives an adjustment screw  1148  in a manner that secures the adjustment screw to the bracket, but allows it to rotate freely in a non-threaded way. A rectangular threaded adjustment nut  1152  is threadedly engaged with adjustment screw  1148  so that when the trigger platform is properly secured to ski  904  and the adjustment screw is turned, the adjustment nut moves longitudinally along the screw (the rotation of the adjustment nut is inhibited by its engagement with the underside of the trigger platform). A spring, here a coil spring  1156 , is provided between fixed screw-guide bracket  1140  and threaded adjustment nut  1152  such that the spring can be selectively compressed/decompressed by turning adjustment screw  1148  so that the adjustment nut moves closer to or farther away from the screw-guide bracket. With this trip torque mechanism  1100 , when trigger platform  932  is properly secured to ski  904 , it can be seen that the trip torque threshold of the trigger platform can be increased by turning adjustment screw  1148  so that adjustment nut  1152  further compresses spring  1156 , and, conversely, the trigger threshold of the trigger platform can be decreased by turning the adjustment screw so that the adjustment nut moves away from screw-guide bracket  1140  and decompresses the spring. In other embodiments, other trigger trip torque adjusting mechanisms may be provided by those having ordinary skill in the art without undue experimentation using the present disclosure as a guide.  
         [0057]     As mentioned above, secondary toe release  936  is secured to trigger platform  932  so that it is pivotable about pivot point  944  in a constrained manner. In this example, secondary toe release  936  is secured to trigger platform  932  using a locking nut/bolt combination  1160  at pivot point  944  and a sliding hold-down mechanism  1164  spaced from pivot point  940 . Sliding hold down mechanism  1164  includes a slidable hold-down  1168  that is fixedly secured to secondary toe release  936  through a slot  1172  in trigger platform  932  using a suitable fastener  1176 . Hold-down  1168  is wider than slot  1172 , and fastener  1176  is tightened to the point that movement of the secondary toe release away from the trigger platform is substantially constrained, but not to the point that the secondary toe release cannot pivot substantially freely.  
         [0058]     Similar to trigger platform  932  relative to ski  904 , secondary toe release  936  is provided with adjustable attenuated release threshold mechanism  1104  that allows a user to set a desired resistance to pivoting of the secondary toe release relative to the trigger platform. In this example, adjustable attenuated release threshold mechanism  1104  includes a screw-guide bracket  1182  fixed to secondary toe release  936  through a slot  1184  in trigger platform  932 . Screw-guide bracket  1182  receives an adjustment screw  1186  in a manner that secures the adjustment screw to the bracket, but allows it to rotate freely in a non-threaded way. A rectangular threaded adjustment nut  1188  is threadedly engaged with adjustment screw  1186  so that the adjustment nut moves longitudinally along the screw (the rotation of the adjustment nut is inhibited by its engagement with the underside of the trigger platform). A spring, here a coil spring  1190 , is provided between fixed screw-guide bracket  1182  and threaded adjustment nut  1188  such that the spring can be selectively compressed/decompressed by turning adjustment screw  1186  so that the adjustment nut moves closer to or farther away from the screw-guide bracket. With this adjustable attenuated release threshold mechanism  1104 , it can be seen that the pivot-resistance of secondary toe release  936  can be increased by turning adjustment screw  1186  so that adjustment nut  1188  further compresses spring  1190 , and, conversely, the pivot-resistance of the secondary toe release can be decreased by turning the adjustment screw so that the adjustment nut moves away from screw-guide bracket  1182  and decompresses the spring. In other embodiments, other attenuated release threshold-adjusting mechanisms may be provided by those having ordinary skill in the art without undue experimentation using the present disclosure as a guide.  
         [0059]     Those skilled in the art will readily appreciate that the embodiment of  FIGS. 9A-11  is merely one example of release logic that provides an attenuated release envelope for shear forces applied in the third quadrant. Following are descriptions of three additional examples to illustrate this point. As will be seen in reviewing these additional examples, there are a number of ways to implement the differing aspects of the release logic, such as the implementation of the trigger and the setting of the trigger trip torque, and the implementation of the secondary toe release and the setting of attenuated-release threshold, among other things.  
         [0060]     Turning now to the first of the additional examples,  FIGS. 12 and 13  each show an alpine ski system  1200  generally similar to ski system  900  of  FIGS. 9A-11  in that it includes a ski  1204 , a third-quadrant release-logic mechanism  1208  mounted to the ski and heel and toe pieces  1212 ,  1216  mounted to the third-quadrant release-logic mechanism. Similar to ski system  900  of  FIGS. 9A-11 , heel and toe pieces  1212 ,  1216  of  FIGS. 12 and 13  may be any suitable alpine heel and toe pieces, if desired.  FIG. 12  shows third-quadrant release-logic mechanism  1208  in an unreleased state, and  FIG. 13  shows the third-quadrant release-logic mechanism in a released state. As described below, third-quadrant release-logic mechanism  1208  includes a trigger  1220  that is generally similar to the trigger mechanism of ski system  900 , above. Heel piece  1212  is secured to an elongate trigger assembly  1224  near the trailing end of the assembly, and similarly to ski system  900  of  FIGS. 9A-11 , toe piece  1216  is secured to a pivoting secondary toe release  1228 . A conventional standard boot sole  1232  is shown for context. As readily seen in  FIG. 13 , ski system  1200  is set up for the right leg of a skier since the pivoting of the toe  1236  of boot sole  1232  is clockwise in response to a shear force being applied to ski  1204  in the third quadrant.  FIGS. 14-16  show details of the various components of third-quadrant release-logic mechanism  1208  that provide the attenuated release of toe  1236  of boot sole  1232  in response to only loads in the third quadrant.  
         [0061]     Referring now to  FIG. 14 , this figure illustrates the various components of third-quadrant release-logic mechanism  1208 . Major components of third-quadrant release-logic mechanism  1208  include: rearward and forward lower mounting plates  1400 ,  1404 ; rearward and forward upper mounting plates  1408 ,  1412 ; a trigger mechanism  1416 ; a trigger trip torque mechanism  1420 ; a secondary toe release mechanism  1424 , an attenuated release threshold mechanism  1428  and a heel piece mounting plate  1432 . As seen in  FIGS. 12 and 13 , heel piece  1212  is fixedly secured to heel piece mounting plate  1432  and toe piece  1216  is fixedly secured to a toe piece mounting plate  1240  of secondary toe release mechanism  1424 . Referring again to  FIG. 14 , forward upper and lower mounting plates  1412 ,  1404  are fixedly secured to ski  1204  using suitable fasteners  1436 . Trigger  1220  includes a pivotable, flexible (in a direction normal to the upper surface of ski) trigger member  1440 , which is captured between forward upper and lower mounting plates  1412 ,  1404  so as to be slightly pivotable about a pivot axis  1444  normal to upper surface of ski  1204 .  
         [0062]     Secondary toe release mechanism  1424  includes in addition to toe piece mounting plate  1240  a pivotable latch  1448  that is captured between trigger member  1440  and forward lower mounting plate  1404 . Toe piece mounting plate  1240  is fixedly secured to latch  1448  and, for the purpose discussed below, the composite of these components is pivotably secured to trigger member  1440  about a pivot pin  1452  so that the toe piece mounting plate and latch (and toe piece  1216  ( FIG. 12 )) pivot in unison under a release condition. The attenuated release threshold for pivoting action of these components is provided by attenuated release threshold mechanism  1428 , which includes a housing  1456  fixedly secured to trigger member  1440  with screws  1460  and a movable cam  1464  and spring  1468  located in the housing. Cam  1464  engages a cam follower  1470  on pivotable latch  1448 . The attenuated release threshold is set using an adjustment screw  1472 , which adjusts the length of spring  1468 , and therefore the force applied by cam  1464  to cam follower  1470 . In the unreleased state of third-quadrant release-logic mechanism  1208 , latch  1448  is securely engaged with a catch  1474 , which as described below, is seated in a groove  1500  ( FIG. 15 ) in trigger member  1440  that inhibits its lateral movement relative to the trigger member, but, as described below in detail, allows it to move longitudinally relative to the trigger member as a result of its interaction with a pin  1476  that is fixed relative to forward upper and lower mounting plates  1412 ,  1404 . When latch  1448  is securely engaged with catch  1474 , the attenuated release of secondary toe release  1228  is not active and toe piece  1216  ( FIG. 12 ) functions as it would in a conventional ski system.  
         [0063]     Rearward upper and lower mounting plates  1408 ,  1400  are secured to ski  1204  using suitable fasteners  1480  and capture the rear end of trigger member  1440  therebetween. Heel piece mounting plate  1432  is fixedly secured to trigger member  1440  so that they pivot in unison with one another about pivot point  1444  of the trigger member when permitted by trigger trip torque mechanism  1420 . In general, it is the lateral loads from heel piece  1212  ( FIG. 12 ) that are the input to trigger mechanism  1420 . A pair of low friction members  1481  that engage a corresponding respective pair of grooves  1482  in trigger member  1440  are provided to reduce the amount of frictional resistance between rearward upper mounting plate  1408  and the trigger member during pivoting of the trigger member.  
         [0064]     Trigger trip torque mechanism  1420  is fixedly secured to ski  1204  via rearward upper and lower mounting plates  1408 ,  1400  and includes a housing  1484 , a T-shaped resistance toggle  1486 , a spring  1488  and an adjustment screw  1490 . Spring  1488  biases toggle  1486  into engagement with a pair of fulcrum pins  1492 A-B that are fixed relative to housing  1484 . Toggle  1486  includes a lever arm  1494  that engages a notch  1496  in trigger member  1440 . As will be described below in more detail, as trigger member  1440  pivots it applies a force to lever arm  1494  of toggle  1486  that works against the biasing force applied to the trigger by spring  1488  as the toggle pivots about the appropriate one of fulcrum pins  1492 A-B. A locking pin  1498  ( FIG. 15 ) is provided so as to capture toggle  1486  between it and one of fulcrum pins  1492 A-B so as to inhibit the toggle from pivoting about the other fulcrum pin. By switching the location of locking pin  1498  ( FIG. 15 ), trigger mechanism  1416  can be set up for either a left-leg ski or a right-leg ski (the right-leg setup being shown). When changing the location of locking pin  1498  ( FIG. 15 ), catch  1474  must also be flipped to change the pivot direction of secondary toe release  1228 . This should become apparent from the following description of the working of third-quadrant release-logic mechanism  1208  relative to  FIGS. 15 and 16 .  
         [0065]     Referring now to  FIGS. 15 and 16 , which are “upside down” views of third-quadrant release-logic mechanism  1208  relative to  FIGS. 12-14 ,  FIG. 15  shows the third-quadrant release-logic mechanism in its unreleased state, and  FIG. 16  shows the mechanism in an attenuated release state caused by a triggering shear force in the third quadrant of ski  1204  ( FIGS. 12-14 ). In  FIG. 15 , the longitudinal centerline  1504  of trigger member  1440  is aligned with the longitudinal centerline  1508  of the ski, latch  1448  of secondary toe release mechanism  1424  is securely engaged with catch  1474 . Consequently, secondary toe release  1228  is securely held by catch  1474  from pivotably releasing. In this state, heel and toe pieces  1212 ,  1216  ( FIGS. 12 and 13 ) act in the same manner they would if affixed to a ski in a conventional manner. Note the location of locking pin  1498  of trigger trip torque mechanism  1420 . In this example, it is located so that trigger member  1440  can pivot only in a counterclockwise direction about pivot axis  1444 . Therefore, any shear loads applied in the second and fourth quadrants will not allow trigger mechanism  1416  to trigger. However, when a shear load is applied to ski  1204  ( FIGS. 12 and 13 ) in the third quadrant, and is counteracted in part by a force applied through heel piece mounting plate  1432 , this shear force causes trigger member  1440  to apply a toggling force to lever arm  1494  of toggle  1486 . Once this toggling force overcomes the resistance and preload of the spring  1488 , trigger member  1440  will pivot about pivot axis  1444 , as illustrated in  FIG. 16 , albeit by a relatively small angle a relative to the ski&#39;s longitudinal axis  1504 .  
         [0066]     Since catch  1474  is laterally captured in groove  1500  in trigger member  1440 , this pivoting of the trigger member causes the catch to move and interact with fixed pin  1476  that is fixed relative to ski  1204  ( FIGS. 12-14 ) via forward upper and lower mounting plates  1412 ,  1404  ( FIG. 14 ). This interaction with fixed pin  1476  moves catch  1474  just enough for latch  1448  to disengage the catch. With latch  1448  disengaged from catch  1474 , it can pivot about pivot pin  1452  once the force applied to toe piece mounting plate  1240  from toe  1236  of boot sole  1232  ( FIGS. 12 and 13 ) is large enough to overcome the attenuated release threshold bias of spring  1468  of attenuated release threshold mechanism  1428 . After the attenuated secondary release has occurred, trigger mechanism  1416  and secondary toe release mechanism  1424  automatically return to their unreleased states. It is noted that the shape of catch  1474  is such that latch  1448  can pivot only clockwise when secondary toe release mechanism  1424  has been triggered and is in a released state. As mentioned above, a right-leg ski setup can be switched to a left-leg setup by flipping catch  1474  generally about longitudinal axis  1508  of trigger member  1440  and by switching the location of locking pin  1498  of trigger trip torque mechanism  1420 .  
         [0067]     While third-quadrant release-logic mechanisms  912 ,  1208  of  FIGS. 9A-11  and  FIGS. 12-16 , respectively, are similar in the context of the ability to utilize conventional heel and toe pieces, the second of the additional examples illustrated in  FIGS. 17-21  utilizes a unique toe assembly  1700  ( FIG. 17 ) that provides the secondary toe release and the adjustable attenuated release threshold without the need for the pivotable secondary release plate. In addition to toe assembly  1700 ,  FIG. 17  shows a conventional standard boot sole  1704  having its toe  1708  engaged with the toe assembly. Referring to  FIGS. 12 and 14 , toe assembly  1200  of  FIG. 17  replaces both of secondary toe release mechanism  1424  and attenuated release threshold mechanism  1428 , but can be used, if desired, with a trigger mechanism and trigger trip torque mechanism substantially similar to, respectively, trigger mechanism  1416  and trigger trip torque mechanism  1420  of  FIGS. 12 and 14 . Modifications to third-quadrant release-logic mechanism  1208  of  FIGS. 12 and 14  to accommodate toe assembly  1700  of  FIG. 17  would include removing the pivotable toe piece mounting plate  1240  and latch  1448 , removing attenuated release threshold mechanism  1428  and removing catch  1474 . Then, toe assembly  1700  of  FIG. 17  would be fixedly secured to forward upper mounting plate  1412 . As seen in  FIGS. 18 and 19 , toe assembly  1700  of  FIG. 17  includes a movable actuator  1800  that is guidably movable within an L-shaped slot  1804  formed in a base  1808  of the toe assembly. Actuator  1800  is movable both pivotably about the longitudinal centerline  1812  of an adjustment screw  1816  and translationably in a direction parallel with longitudinal centerline  1812 . It is this movable actuator  1800  that trigger member  1440  ( FIG. 14 ) would pivot above longitudinal centerline  1812 . For reasons that might not be apparent until after reading the following description, trigger member  1440  would need to be slotted substantially along its longitudinal axis ( 1504 ,  FIG. 15 ) to allow the actuator to translate along longitudinal centerline  1812  of adjustment screw  1816 . Otherwise, the trigger member and trigger trip torque mechanism for toe assembly  1700  may be the same as shown in  FIG. 14 . Those skilled in the art will readily appreciate that third-quadrant release-logic mechanism  912  of  FIGS. 9A-11  may also be modified in a similar manner. In addition, it is noted that the trigger for toe assembly  1700  of  FIG. 17  may be of some other type, such as an electronic trigger that is responsive to input from, e.g., one or more force, displacement and/or acceleration transducers.  
         [0068]     Referring to  FIGS. 17, 20  and  21 , in addition to base  1808 , actuator  1800  and adjustment screw  1816 , toe assembly  1700  includes a toe retainer  1712  movably secured to the base, for example, by a pair of studs  1716 A-B. Toe retainer  1712  includes a pair of L-shaped slots  1720 A-B that, under the right loading conditions, allows the toe retainer to pivot either clockwise or counterclockwise so as to release toe  1708  of boot sole  1704 . Toe retainer  1712  is biased into engagement with studs  1716 A-B by a force-applying member, such as housing  1724 , that is movable relative to base  1808  and that, in turn is biased by either one or both of springs  2000 ,  2004  ( FIGS. 20 and 21 ) located within the housing, depending on whether or not toe assembly  1700  is in its unreleased or released state.  
         [0069]     Referring to  FIGS. 20 and 21 , adjustment screw  1816  has a left-hand thread region  2008  and a right-hand thread region  2012 , with actuator  1800  located between these two regions. Each of the left- and right-hand thread regions  2008 ,  2012  is threadedly engaged by a corresponding movable stop  2016 ,  2020  that moves in an opposite direction from the other when adjustment screw  1816  is turned. In this manner, either both springs  2000 ,  2004  are being compressed or both springs are being decompressed, depending on which direction adjustment screw  1816  is turned. Actuator  1800  is not threadedly engaged with adjustment screw  1816 . Rather, adjustment screw  1816  is free to rotate within an unthreaded opening in actuator  1800 . However, actuator  1800  is substantially fixed from moving along longitudinal centerline  1812  of adjustment screw  1816  using, in this example, a C-clip  2024 A-B on either side of the actuator that engages a corresponding groove  2028 A-B (only groove  2028 A can be seen) in the adjustment screw.  
         [0070]     Consequently, and referring to  FIGS. 17-21 , toe assembly  1700  operates as follows to provide a “normal” release (i.e., a release akin to the release of a conventional binding secured to a ski in a conventional manner) and an attenuated release in response to a suitable shear loading in the third quadrant. With actuator  1800  in its unreleased position, i.e., locked in the transverse portion  1820  of slot  1804  as shown in  FIGS. 18 and 20 , only spring  2000  is active in biasing housing  1724  against toe retainer  1812 . Therefore, the force applied to toe retainer  1812  is equal to the spring constant of spring  2000  multiplied by the compression of this spring. However, when actuator  1800  is triggered and moved into its released position in the longitudinal portion  1900  ( FIG. 19 ) of slot  1804  in base  1808  as shown in  FIGS. 19 and 21 , housing  1724  is now biased by both springs  2000 ,  2004  (assuming the longitudinal portion of slot  1804  is long enough to not interfere with activation of the second spring  2004 ). If springs  2000 ,  2004  have equal spring rates and are compressed the same amount, the effective force of housing  1724  on toe retainer  1712  remains the same as before but the combined spring rate is halved in this example. Of course, the spring constants, compression distances and other variables will be selected so that both the unreleased and attenuated release forces housing  1724  applies to toe retainer  1712  will be selected to achieve the desired results, which in the context of the present invention includes inhibiting ACL injuries. Referring to  FIG. 18 , it is noted that the right-leg set up of toe assembly  1700  ( FIG. 17 ) can be changed to a left-leg setup by locating longitudinal portion  1900  ( FIG. 19 ) of slot  1804  in base  1808  on the other side of transverse portion  1820 .  
         [0071]     Whereas the embodiments of  FIGS. 9A-21  are generally purely mechanical in nature, the third-quadrant release logic described above in connection with  FIGS. 1 and 5 - 9  can be implemented electronically using either a digital controller or an analog controller, or a combination of both.  FIGS. 22-24  illustrate one example of a ski system  2200  that includes an electronic third-quadrant release-logic binding system  2204 . Referring first to  FIGS. 22 and 23 , binding system  2204  includes a base  2208  that supports heel and toe pieces  2212 ,  2216 . For context, a conventional ski boot sole  2218  is shown being clamped between heel and toe pieces  2212 ,  2216  as it would during an unreleased state of electronic binding system  2204 . Base  2208  is secured to a ski  2220  so as to be substantially fixed in the fore and aft direction relative to the ski and also substantially fixed in a direction normal to the upper surface  2224  of the ski. However, base  2208  is secured to ski  2220  so as to be movable laterally relative to ski. In this example, base  2208  is secured using three studs  2300 A-C that are fixed to ski  2220  and engage corresponding respective slots  2304 A-C in the base. As those skilled in the art will appreciate, in this example studs  2304 A,  2304 C include a head (not shown) that engages base  2208  in a manner that inhibits movement of the base in a direction normal to upper surface  2224  of ski  2220 .  
         [0072]     Electronic binding system  2204  also includes at least two sensors for sensing information regarding the lateral (shear) forces being transmitted between base  2208  and ski  2220  at two distinct locations along the longitudinal axis of the ski. In this example, such sensors are two pairs of load cells  2400 A-D ( FIG. 24 ) that are fixed to ski  2200  by corresponding load cell supports  2300 A-B ( FIG. 23 ) and extend into corresponding respective cavities  2312 A-B in base  2208 . As is seen more particularly in  FIG. 24  and as described below, with this arrangement, load cells  2400 A-D are able to sense the lateral forces between base  2208  and ski  2220  at two distinct locations. In this example, each of heel and toe pieces  2212 ,  2216  is responsive to a trigger signal to cause a release of boot sole  2218 . As those skilled in the art will readily appreciate, heel and toe pieces  2212 ,  2216  may release in any of a number of manners. In the example shown, heel piece  2212  releases the heel of ski boot  2218  vertically, whereas toe piece  2216  releases the toe of the ski boot by pivoting laterally, in the manner of toe assembly  1700  of  FIGS. 17-21 . Indeed, toe assembly  1700  of  FIGS. 17-21  may readily be adapted for use with electronic binding system  2204  of  FIGS. 22-24 , by providing a suitable actuator  2316  ( FIG. 23 ) for moving actuator  1800  ( FIG. 18 ) of toe assembly  1700 . Actuator  2316  of  FIG. 23  may be any suitable electronic or electromechanical actuator. In this example, electronic binding system  2204  would also be provided with a suitable electronic or electromechanical actuator  2320  ( FIG. 23 ) for activating the release of heel piece  2212 . In other embodiments, toe piece  2216  may be replaced by a vertical-release toe piece (not shown) that releases vertically in the manner of heel piece  2212 . In yet other embodiments, only toe piece  2216  or heel piece  2212  may provide the desired release.  
         [0073]     Electronic binding system  2204  includes a controller  2324  for implementing the release logic. Controller  2324  may be either a digital controller that utilizes, for example, a microprocessor such as an application specific integrated circuit (not shown), or an analog computer, or a combination of both. Those skilled in the art understanding the release logic of electronic binding system  2204  will readily be able to implement a suitable controller  2324  without undue experimentation. Similarly, those skilled in the art will readily understand how to implement all communications required between/among actuators  2316 ,  2320 , sensors  2400 A-D and controller  2324  using any suitable wired or wireless technology, or a combination of both. Therefore, such details are not presented in  FIGS. 22-24 .  
         [0074]     Referring now to  FIG. 24 , this figure is used to explain the release logic used by electronic binding system  2204 , and particularly controller  2324 , to release heel and toe pieces  2212 ,  2216  with an attenuated release in response to virtual forces Fy in quadrant  3  that exceed a predetermined trigger trip threshold. Of course, the release logic in the other quadrants  1 ,  2  and  4  may be programmed so that heel and/or toe pieces  2212 ,  2216  provide an appropriate non-attenuated release relative to the third-quadrant attenuated release. In  FIG. 24 , base  2208  is shown in cross-section to expose load cells  2400 A-D and corresponding cavities  2304 A-B and ski  2208  is shown for context.  
         [0075]     For consistency with the analyses corresponding to  FIGS. 1-8  and with the implementations of the embodiments of  FIGS. 9A-21 , the reference axis used for the release logic of electronic binding  2204  is the tibial axis  2420 . With this reference, the torque T (which is equivalent to Mz in the context of  FIGS. 1-8 , above) about tibial axis  2420  is T=T 1 +T 2 . Since only one load cell  2400 A-D in each of cavities  2304 A-B can be loaded (with a compressive load) at a time, the output forces F A , F B  of load cells  2400 A,  2400 B can be added, and the output forces F C , F D  of load cells  2400 C,  2400 D can be added such that F A +F B =F 2  and F C +F D =F 1 . Therefore, T=(L 1 ×F 1 )+(L 2 ×F 2 ), where L 1  is the distance between tibial axis  2420  and the transverse (relative to ski  2220 ) centerline of load cells  2400 C,  2400 D and L 2  is the distance between the tibial axis and the transverse centerline of load cells  2400 A,  2400 B. The virtual force Fy on ski  2220  is the sum of F 1  and F 2 , i.e., Fy=F 1 +F 2 , and the position, P, of the virtual force Fy relative to tibial axis  2420  is determined by P=T/Fy.  
         [0076]     As will be appreciated, the quadrant of virtual force Fy is determined by the signs of position P and torque T. Here, for quadrant  3 , position P is negative and torque is positive. For the attenuated quadrant  3  release, the attenuated release logic of controller  2324  is designed to trigger actuators  2316 ,  2320  when the value of calculated torque T exceeds the value of the predetermined release torque calculated from the appropriate equations for the trigger trip torque and attenuated release torque, which are represented graphically for one example in  FIG. 7 , above. In other words, if T is greater than both the trigger trip torque and the attenuated release torque, then controller  2324  will send a release signal to actuators  2316 ,  2320 . This same procedure can be used in all other quadrants with as much complexity as is required to satisfy the desired retention threshold in each quadrant. The raw forces F 1  and F 2  can be sampled and filtered to best predict the true loads on the lower extremities of a skier using ski system  2200  ( FIG. 22 ). A mechanical spring (not shown) may, for example, be used in series with each of load cells  2400 A-D to filter out very short duration loads that likely do not impact ACL injury.  
         [0077]     Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.