INFORMATION FOR ENGINEERS, ORTHOPEDIC SURGEONS, EPIDEMIOLOGISTS AND PHYSIOLOGISTS
The release decision of a ski-binding is based on the structural capacity of individual tibia physiology — plus a margin — as indirectly prescribed by the international alpine ski-binding standards, ISO 9462 and ISO 8061. Howell SkiBindings also provide a unique 3rd-mode of non-pre-releasing lateral heel release that favorably-exceeds these minimum international standards — plausibly providing ACL-friendly and MCL-friendly skiing, too (see Part 2, below).
Ski-bindings are force-imparting and force-sensing mechanisms that — when combined together with the length of the boot sole — react to (a) torsional-torque about the long-axis of the tibia through the use of a non-pre-releasing toe-piece; (b) forward bending-moments about the long-axis of the tibia through the use of a non-pre-releasing heel-unit (see footnote-1 for the engineering-definition of 'moment'); (c) strain across the ACL and the MCL through the use of an open-art, non-pre-releasing lateral heel release mechanism that is uniquely built into the heel-unit of Howell SkiBindings (see Part 2, below).
For important information about the retention-function of ski-bindings, see the other sub-tab — 'Retention' (retention is the 1st functional requirement of a ski-binding).
Part 1 — Tibia-Friendly Release
Technical definition, tibia-friendly release
Ski-bindings limit their holding-force — in conjunction with the position of the fulcrum-points that are stationed between the boot and the ski — by converting potential injury-producing loads (footnote 2) that are applied to the tibia into a release-response.
When engineering a building-structure it's essential to know the strength of concrete, steel, wood and the strength of the other construction materials that form the structure. The same principle applies to ski-bindings: first, we must know the strength of the tibia to mitigate injury to the tibia.
Strength of average male tibia
The 'average' adult male tibia fractures at ~11.3 daNm during slow-torsion and ~25 daNm during slow forward-bending. These average values apply to male skiers who weigh ~170-pounds and who are aged between 20 and 53 years. The full range of tibia fracture-limits in torsion, bending, and combined torsion-bending — as a function of weight, age and gender — are documented in the biomechanical data of Ernst Asang of Munich, Germany [footnotes 3]. For practical use with ski-bindings, Asang's tibia-fracture data is reorganized, biomechanically [footnote 4]. This essay discusses some of Asang's reorganized tibia-fracture data.
Weakest section of the tibia
The tibia is weakest in bending where skiing stresses are also the largest — near the top of the boot. In torsion, the top two-thirds of the tibia are the most vulnerable sections.
No protection of the tibia by muscle activity
Muscle activity cannot add strength to the tibia because skiing injury-loads can occur faster than 'fast-twitch' muscles can be turned-on. Inversely, there is no experimental, epidemiological or observational scientific proof that muscle activity can subtract appreciable strength from the tibia. The failure criteria of the tibia must therefore be based on the most conservative condition — the unprotected tibia.
The role of the ski-boot
The desire for complete "tibia safety in skiing" is impossible since, for example, during some injury-producing events, the boot can be partially constrained by snow — causing an injury-producing load to not flow through the binding. Boot-fit and boot-buckling contribute significantly to the transfer of loads between the ski and the tibia: a binding cannot read or react to loads that are not transmitted to a binding as a consequence of a ‘weak-link’ between the foot / leg / ski-boot. If a boot is buckled too loosely — an injury-producing-load cannot be fully-transferred to the binding. Boots must be buckled snugly.
Factors effecting tibia strength
• Tibia diameter / skier weight — The diameter of a cylinder effects its strength in torsion. In the case of bending loads, strength is effected by the ratio of the diameter to the length. In practice, large variation in the clinical-measurement of tibia-diameters is an uncontrollable problem, even when the measurement is performed by orthopedic surgeons [footnote 5]. Therefore, the measurement of tibia diameter is impractical for selecting ski-binding settings. However, (1) tibia diameter correlates to skier weight — if the skier is not over-weight. A correction for an over-weight condition is determined by the ratio of the skier's height-to-weight. Over-weight corrections — based on height — are found within all of the ski-binding release adjustment charts that are supplied by all of the binding manufacturers. Corrected skier-weight is a practical predictor of tibia strength. Further, however, (2) the application of x-ray-derived tibia anthropometrics for research — such as tibia diameter metrics that relate to the strength characteristics of the tibia — is essential to define ski-binding function at the binding-manufacturer level.
• Age related tibia strength — Children and adolescents under 19-years have soft-weak bones. Females over 40 have the possibility of reduced bone strength. Males over 53 have the possibility of brittle-weak bones. See graph, below. Reasonable exercise and diet (see text, below) can mitigate a large reduction in tibia strength.
• Velocity of loading — Bones are stronger during 'fast' (dynamic) loading compared with slow (quasi-static) loading. The velocity-effect on bone-strength is called 'visco-elasticity'. There can be as much as an ~18% difference in tibia-strength between slow and fast loading. Ski-bindings must function to accommodate the worst-case scenario — slow loading — even though the issues of friction that are found in nearly all mechanical systems become compounded during slow-moving mechanical operations. See graph, below.
• Combined-loading — Bones are weaker during combined torsion-bending loading when compared with pure-torsional loading. See graph, below.
• Cyclical stress / exercise — As described by Wolfe's Law, bones can become stronger when exposed to repeated cyclical loading. Racers who ski extensively on hardpacked snow and ice can develop stronger tibia's. Astronauts — in the absence of gravitational loading — experience weakened bones.
• Diet — A calcium-rich diet together with vitamin D can mitigate a reduction in bone strength. Excessive phytates (non-soaked beans), meat, salt, oxalates (such as spinach), wheat bran, caffeine (coffee & tea), alcohol and soft drinks are adverse to bone strength [ref: U.S. National Osteoporosis Foundation].
• Disease — Certain diseases can reduce bone strength. A doctor should provide medical advice about whether skiing is appropriate during the course of certain diseases.
• Gender — When comparing male tibia strength to female tibia strength, there is no difference in the strength of the same size tibia's — noting of course that the average size of male and female tibia's are different. However, natural calcium depletion in older females can reduce bone strength if calcium is not supplanted (vitamin D is also needed to cause calcium supplements to become effective);
• Previous fracture — Properly healed, a bone has the possibility of becoming stronger than normal (but don't count on it being stronger than normal), and bones that are supplanted with titanium pins can become stronger after bone-fibers grow into the titanium (but here also, don’t count on it being stronger). Bone fractures that are not fully healed can be significantly weaker than normal-strength bones. Skiing should not take place until after a fractured tibia is fully-healed (typically, 10-weeks after proper medical care ... but this time-duration can vary depending many factors that must be assessed by a doctor).
• Other factors — There are other biomechanical and physiological factors that effect tibia strength, but the above factors are the main factors.
Nothing written here should be construed as medical advice: please consult a doctor for medical advice.
Practical reality of ski-binding release-settings.
The relationship between an individual's unique physiology and bone strength is significant. Ski binding release settings are 'adjustable' expressly to attempt to accommodate the prime factors that effect tibia strength — but it's impossible to dial-in a binding's release settings to become perfectly aligned with all of the above-noted factors because they are difficult to quantify in a 'net result'. This is one of many reasons why 'release settings' should be aligned with a binding's ability to supply 'retention' at low release settings (please see 'Retention' sub-section).
Engineering-philosophy differences about ski-binding function & release settings
There are long-running debates between the Germanic and the French approaches toward the interaction between ski-binding function and release settings.
The Germanic approach is to design the binding to supply maximum retention. Then, if the retention-function of the binding is performing as defined in the 'Retention / Anti-Pre-Release' section of this website — the binding's setting is adjusted to a biomechanical release threshold.
The French approach is to design the binding to supply maximum multi-directional release. Then, if the release-function of the binding is performing as defined throughout this essay — the binding's setting is adjusted to a skiable retention threshold.
Howell SkiBindings company believes that a binding's design must functionally-decouple the release-function from the retention-function — as in 2 separate systems. The binding's setting can then be adjusted to a certain 'pre-setting' based on the guidelines of international standard ISO 8061. The pre-setting can then be fine-tuned through the proper use of the 'Self-Release Method' (see below). With Howell SkiBindings it appears that most skiers can leave the pre-settings — as recommended by ISO 8061 — unchanged.
Only Howell SkiBindings are fully-functionally-decoupled between the retention-function and the release-function:
The principles of Axiomatic Design Engineering, formalized as the first new engineering discipline in over 100-years by MIT Engineering Professor, Nam Suh, are utilized robustly in developing new Howell SkiBindings. In this way, release is smooth — only when needed, biomechanically — and retention / anti-pre-release is powerful — always available when performing controlled, aggressive, skiing. Only Howell SkiBindings deploy fully-decoupled Axiomatic Design Engineering technology. Only Howell SkiBindings deliver powerful anti-pre-release independently of the settings. Howell SkiBindings are uniquely the 1st bindings that can be skied at 'chart settings' without pre-release. This is a 1st within the category of alpine ski bindings.
Self-Release Method 
Strong, fast, aggressive skiers and racers who need settings higher than the ‘recommended settings’ on the Howell Release Adjustment Chart can use the Self-Release Method to obtain special 'discretionary settings' — only when the method is used correctly. The correct Self-Release Method also helps to (a) assure that the settings that are necessary for strong, fast, aggressive skiers are not grossly overtightened / not too high / as is otherwise typical in the absence of using the Self-Release Method; and (b) — for all levels of skiers — the Self-Release Method helps to assure that there is no ‘gross impediment to release’.
First — together with your skis and boots — have Howell SkiBindings mounted and adjusted for proper function by a Certified Howell SkiBinding Technician (you can become one, on-line).
Next, select the proper ‘pre-setting’ from the Howell Release Setting Chart . Adjust the binding’s indicator-settings to the chart-recommended ‘pre-settings’.
Forward Heel Self-Release Setting:
- Stand on one foot only with the boot firmly buckled as it is buckled during skiing.
- The ski must not be held fixed.
- Release the heel by assertively moving the top of the lower leg forward-and-downward — toward the near-forebody of the ski. Not too fast. Do NOT lunge forward with the opposite leg because this action can rupture the achillies tendon. Hold the back of a turned-around dining-room chair to mitigate falling.
- Readjust the heel setting until release occurs at the ‘comfort threshold’.
- Do not repeat this test more than 4 times with one leg in one session.
Lateral Toe Self-Release Setting:
- Place one ski on its inside edge by moving the knee slightly-inward; place weight on the ball of the foot; then slowly but assertively — cause the toe of the boot to move inward ... toward the ground … to cause full-lateral-toe-release. Fast movement must be avoided because this action does not cause the desired effect that is necessary for proper selection of the binding’s setting.
- Readjust the toe setting until full-release occurs at the ‘comfort threshold’.
- Do not repeat this test more than 4 times with one leg in one session.
Lateral Heel Self-Release Setting:
• Match the lateral toe setting that is derived by the Self-Release Method onto the lateral heel indicator-setting.
WARNINGS ! Injury can occur during improper use of the process to seek settings that are derived by the Self-Release Method: follow the above process, closely, to avoid injury. During skiing, lowered settings may cause inadvertent pre-release; increased settings may block necessary-release; Self-Release settings are ineffective if the binding is not supplying proper function as defined in the Howell SkiBindings Technical Manual.
A Howell Certified Technician should (optionally) measure the release of the complete ski-boot-binding system using measuring instruments — lateral-toe; forward-heel; lateral-heel — as described in the Howell SkiBindings Technical Manual; take appropriate service-action if necessary; record the measurements; provide a copy of the recorded measurements to the skier; provide Howell SkiBindings in-box instructions to the skier.
We require that all Howell SkiBindings are mounted and serviced by a Howell SkiBindings Certified Technician (you can become one, on-line) — and we recommend that you know your settings and know what constitutes proper ski binding function. Please see the complete in-box instructions that are supplied with Howell SkiBindings for all of the necessary service-information.
Howell SkiBindings have been designed to release the ski from the boot laterally at the toe; vertically-downward as well as laterally-outward at the heel — (3 modes) — and to retain the ski to the boot during controlled skiing maneuvers. Despite these features, injury may result from simply falling down or from impact with an object. An appropriately functioning ski binding may not release under all injury-producing circumstances. Skiing, like all athletic endeavors, involves a certain degree of risk that must be recognized and accepted. Additional information about the care and maintenance of Howell SkiBindings can be reviewed in the Howell SkiBindings in-box instructions and through the on-line Howell SkiBindings Help Center.
 This optional Self-Release Method is not part of ISO 8061 or any standards.
 The recommended settings on the Howell Release Adjustment Chart conform to ISO 8061 and conform to related provisions within ISO 9462. Boots must conform to ISO 5355. Howell SkiBindings are not compatible with AT ski boots that have metal inserts for pin-bindings. Howell’s SkiBindings are Grip Sole compatible with the use of the optional Grip Sole AFD’s that are supplied, standard, with each purchase.
Testing the release-function of alpine ski-bindings.
Proper 'testing' of the release-function of the complete ski-boot-binding system must involve the use of properly calibrated release measuring instruments by a certified ski-binding technician. Testing with measuring instruments should take place at least once every 30-days of skiing — or before the beginning of each ski season — which ever comes first.
Levels of ski-binding testing
Release testing ski-bindings can be performed at many levels — skier, retailer, distributor, manufacturer, or independent testing lab. Testing ski-bindings for release — at any level — can focus on demonstration, calibration, or scientific validation. We respectfully encourage you to ignore blogs and 'published' ski-binding test reports that do not involve the use of release measuring instruments.
Consumer-level ski-binding 'inspection'
Beyond the Self Release Method to fine-tune settings and identify gross impediments to release — skiers should come to know what constitutes proper ski binding function. Howell SkiBindings in-box instructions provide a wealth of information in this way (link under construction).
Retailer-level ski-binding testing
At the retailer-level, there are several visual and tactile tests that must be performed — as required by Howell SkiBindings certification / indemnification programs (link under construction). Uniquely, skiers can also become Qualified Mechanics by Howell SkiBindings company. Standards are in-place by the American Society for Testing and Materials (ASTM) that guide ski retailers on generic ski-binding testing procedures.
The objective of consumer and/or retailer ski-binding release-testing is to assure that the actual release-limits that are being measured are testing within the expected release tolerances that are supplied by each respective ski-binding company. If the actual release-limits are measured to be outside of the expected release tolerances — then service must be performed to the binding, the boot, or both, as specified by Howell SkiBindings. If after proper service is performed the measured release still remains outside of the expected tolerances, the binding should be returned to Howell SkiBindings company; the boot should be returned to the boot company; both should be returned to their respective origins for service or warranty replacement; or if the binding is outside of the warranty-period, the binding should be retired — not sent to a 2nd-hand event.
Manufacturer-level release-testing for tibia-friendly skiing
Above and beyond the minimum international ‘release’-standards, ISO 9462 and 8061 — to which standards all binding companies must comply — release should occur in a way that limits the selected peak-torsional-torque and limits the selected peak-bending-moment on the tibia — to be as nearly as constant as possible — independently of the location of where almost any injury-producing force enters the ski. This requirement is a fact of nature: a tibia cannot 'know' where a potential injury-producing force enters a ski. To quote Nobel Prize winning scientist, Francis Arnold— “Nature does not care about our calculations.”
However, in practice, it is nearly impossible to achieve a constant peak-release-load into the tibia independently of where a force enters a ski because (a) the ski is a lever where the applied force can become concentrated at many possible locations; and (b) the pivot-points between the ski and the boot — in both torsion and in bending — are not always aligned with the weakest points of the tibia. Never-the-less, it's the belief of Howell SkiBindings that each binding manufacturer should try to seek a nearly-constant load on the tibia, at release, no matter where an applied force enters the ski. Some binding companies achieve this scenario better than others. Why? Because most binding companies explore binding function only through Annex-A of ISO 9462 and ignore the ‘optional alternative’ Annex-B. But the key to how a binding should behave, biomechanically, is exposed in Annex-B, not in Annex-A. Annex-A is mostly about how a binding should behave at the end of the manufacturing assembly-line (which has a different significant importance). Several so-called leading binding companies do not even have the equipment to test according to Annex-B ! ( It appears that no pin-binding companies test according to ISO 9462 Annex-B: clearly, pin-binding companies have no bona fide understanding of ski-binding design/function that addresses basic human-biomechanics — but they do seem to be experts at manufacturing.)
Method to measure load-consistency on the tibia
To approach the goal of achieving a constant peak release-torque and a constant peak forward-bending release-moment on the tibia — no matter where a trauma-force enters the ski — test-forces are applied to a range of positions along the length of an unconstrained ski, while at the same time a standardized test-sole is rigidly held by a surrogate metallic foot / tibia — while measuring the resulting torque and bending-moment on the surrogate metallic tibia. In essence, this is the type of testing that is defined by ISO 9462 Annex-B. Unlike the type of release-testing that is conducted by ski shops (and by TÜV while using ISO 9462 Annex-A), the ski is not held fixed when conducting tests according to Annex-B. In Annex-B, the opposite (proximal) end of the tibia is rigidly connected to a test frame while the ski floats in unconstrained space. This special type of test apparatus allows the simulation of 'rigid-body mechanics' at peak release-loading conditions — in a way that allows the ski to 'float' as it would during actual skiing. This method allows functional decoupling of the test device from the unique kinematic function of each binding design. By allowing the ski to freely float during release, each binding design’s unique kinematic path of motion can control the ski’s path of release. The ski’s release-path, relative to the surrogate tibia’s position, directly effects the resultant peak-load on the tibia at release. Unless properly engineered, the unique kinematics that are generated by each unique binding design have the possibility of varying the peak-loads into the tibia — at levels that far exceed any given release setting. Testing according to ISO 9462 Annex-A does not explore kinematic function. Decoupling the test device from the kinematics of the ski-binding provides a clear unconstrained exploration of each binding design’s unique kinematic function with respect to the variation in the loads that flow into the tibia when applied-forces enter the ski in varying locations. The exploration and understanding of special ski-binding kinematics — through experimental testing as noted above — is therefore, essential for the development of top performing ski-binding function. Binding companies that do not engage in the above process are not only lazy — but in the opinion of Howell SkiBindings — they are incompetent and they are misleading skiers and ski shops about their bindings’ less-than-stellar function ... even if they meet the minimum safety standards according to Annex-A. Meeting minimum standards is not the same as providing exceptional performance. There is even one alpine ski-binding company that sells and ships bindings that does not meet minimum safety standards according to Annex-A or B !
Expressing the results
A graphic representation of the test-results obtained from the use of the above test method (ISO 9462, Annex-B) can be depicted by plotting ‘release envelopes’. ‘2D release torque envelopes’ express the peak torsional torque that is applied to the tibia as a specific point in graphic-space that is plotted laterally of the center-line of a graphic-ski — laterally of each graphic-point where a test-force is applied to a ski. Each point in graphic-space that corresponds to each point where the force is applied to the ski can then be graphically-connected to form a 2D 'release-envelope' — a composite of many related tests. The ideal shape of a 2D release-torque-envelope is a straight line that is parallel to the ski, originating 45cm forward of the projected-axis of the tibia and another line parallel to the ski that originates 45cm aftward of the projected-axis of the tibia. This ideal 2D graphic-representation would depict a binding that limits the torsional torque that is applied to the tibia — to a constant magnitude — no matter where the test-force is applied along the length of the ski, forward of 45cm or aftward of 45cm of the projected axis of the tibia. ‘See the release torque envelopes, below.
(( The valgus (abduction) moment release envelopes are discussed in Part-2, below. ))
Practical considerations for tibia-friendly ski-binding function
A binding must address the functional relationships between applied-force, leverage, fulcrum-positioning, torsional-torque and forward bending-moments to modulate consistent loading into the tibia.
Influence of fulcrums on tibia-friendly ski-binding function
As noted above, the magnitude of the resultant-loading into the tibia is caused not only by the binding’s release setting but also by the kinematic path of the ski’s release — which path is controlled by the location of the torsional-pivot-points and by the forward-release-fulcrum-points between the boot and the the ski — relative to the position of the tibia.
The leverage-effect supplied by the length of the ski boot is also important. Its effect is defined by the distance between the toe-piece of the binding and the center-of-rotation between the boot and the ski — relative also to the position of the projected-axis of the tibia — during torsional-release. In the case of forward-bending release, the leverage-effect is defined by the distance between the heel-unit and the leading edge of the anti-friction-device (AFD) that's located under (or near) the ball of the foot. The leading edge of the AFD forms the fulcrum for forward release.
In these 2 modes of release — lateral at the toe and vertical at the heel — it's important to remember the simple relationship of torque = force X distance. The equation is not, torque = 2(force) X distance ... or 3(force) X distance. Distance (leverage) has an equal effect on torque as does force. Release torque is not controlled solely by changing the force setting of the binding. The built-in design of a ski-binding's pivot-points in torsion and bending — the distance between the force-imparting mechanisms of the bindings and the pivot-points and fulcrums — has an equal effect on the resultant load that is applied to the tibia as does the force supplied by the binding toe-piece or heel-unit [see footnote 7]. All Howell SkiBindings deploy this functional-element of uniquely building-in specially-positioned pivot-points and specially-positioned fulcrums to flatten the release-torque-envelope as best as possible, forward of 45cm and aftward of -45cm from the projected axis of the tibia — thus holding the peak torque and peak bending-moment that is applied to the tibia as close to 'constant' as possible no matter where an injury-producing force enters the ski. This special, nearly-constant, release effect that is uniquely supplied by Howell SkiBindings can actually be 'felt' by skiers during necessary release. The 'feeling' is a ‘remarkably smooth release’.
Unique functional-signature of each binding design
Each binding design produces a unique release-envelope shape — a unique signature.
Please note that unlike the large amount of information about the function of a binding that is expressed in a release-envelope, a ‘release-setting’ simply moves the entire release-envelope upward or downward: different release-settings do not change the shape of a release-envelope. Different release settings do not change the unique kinematic-function of each binding design.
Combined-loading-function of ski-bindings — for tibia integrity
All structures become weaker during combined loading. During the combined loading that naturally occurs while skiing, the tibia becomes weaker, too. Graphically representing the results of ski-binding release-function during combined loading is accomplished through the use of 3D release-envelopes. A combined-load test involves the application of a preload in one direction — for example, a forward bending-moment — then, a lateral load is applied to the ski until it releases from the boot. The forward-bending preload is represented, graphically, in the 3D release-envelope, by plotting a point a certain distance above the top surface of the ski: this distance represents the magnitude of the applied forward-bending pre-load. Another point is then applied to the graphic presentation — laterally of the pre-load plot — at a distance that is proportional to the peak torsional torque that is resolved into the tibia at release. Similar plots are generated to represent the resulting combined-load on the tibia — at release — when forces are applied to varying locations along the length of the ski. Each successive test along the length of the ski can become connected in graphic-space. This approach generates a 3-dimensional release-envelope. An ideal 3D release-torque-envelope is shaped like 2 rectangular boxes — one box positioned 45cm forward of the projected-axis of the tibia, the other box positioned 45cm aft of the projected-axis of the tibia. In practice, there are distortions in 3D release-torque-envelopes, too, that are caused by the positions of the lateral-release-pivots and forward-release-fulcrums that are located between the boot and the ski, relative to the position of the tibia. Bindings that produce small distortions in the graphic release-envelopes hold the peak loading into the tibia (in both torsion and bending) closer to constant compared with bindings that have larger graphic-distortions in their release-envelopes.
Howell Ski Bindings have the least distorted 2D and 3D release-envelopes of any ski-binding. This outstanding function is accomplished through the use of dual-alternate pivot-points in torsion and by locating the leading edge of the AFD as far aft of the tip of the boot as possible.
(( The unique AFD-location of Howell SkiBindings provides additional benefits for edge-control, too. ))
Overall epidemiology of tibia fractures in skiing
Previously-classic spiral and green-stick (bending) tibia-fractures involving adult skiers barely exist today. They have a prevalence of only ~3% of all skiing injuries and an incidence (not 'incidents') of ~20,000 mean-days-between-injuries (MDBI). This data implies that adult alpine ski-bindings and their related release-settings are doing their job — a very good job. However, It is important to note that other bindings that do not supply strong retention-function — but are set for release according to standard guidelines — can pre-release. Pre-release shifts injury-patterns to upper-body injuries such as to the head, spine, shoulder, wrist, spleen, etc. Upper body injuries can be far more severe than tibia fractures. Pre-release can be averted through robust binding design/function precluding the need for elevated release settings (see sub-topic — ‘Retention’).
Sub-notes regarding tibia-friendly ski-binding release function
1— Tibia fractures among children-skiers are on the rise (prevalence = 5% of all children's skiing injuries; incidence = 36,000 MDBI — compared with 3% and 45,000 MDBI 12-years ago). Children must have low-friction interfaces between boots and bindings. Children's boots must have upper-shells that are made of materials that are semi-hard, above 50 D-Shore, in order for the ski-boot-binding system to provide proper release-function and proper retention-function by decisively transferring injury-producing loads that flow between the snow and the skiers’ legs — into the bindings. Children's boots must be well fitting — not overly-large to grow into. Boots must be firmly buckled at all times while skiing. 'And children's bindings should include a low-friction AFD with a well-defined leading edge (a well-defined fulcrum) that is located ~3cm aft of the tip of the boot sole.
2— Significantly, other types of previously obscure tibia-fractures are now on the rise: severe, high-energy tibia-plateau fractures, severe tibial-tuberosity fractures, and high-energy spiral-tibia-fractures are greatly on the rise. Each of these types of tibia-fractures presently comprise the fastest-growing categories of injuries in skiing — paralleling the advent of fat-skis and pin-bindings (causation is still not linked, epidemiologically — but is strongly observed, clinically). The high-energy nature of the new types of skiing fractures involve multiple-fragments, difficult surgical reconstruction, and 10 to 15-months of aggressive rehabilitation. Many skiers who sustain these new types of tibia fractures never ski again. Fat skis on firm snow; and pin-bindings in any snow (except Trab TR2 pin-bindings) — are a serious problem for the sustainability of our beautiful sport. Howell SkiBindings principle, Rick Howell, has tested and generated extensive release-envelope data involving 20 brands of pin-bindings. All pin-binding release-function (except the Trab TR2) is horrendous at best, many times requiring 2 Very High Level releases in order for the ski to fully-separate from the boot ... meaning that the tibia becomes fractured twice during one injury-producing event. Further, pin bindings have nearly zero lateral elasticity — thus causing 'high-energy' tibia fractures involving many bone-fragments. Fat skis are causing tibia-tuberosity fractures (and MCL-injuries) because the wide-width of fat skis — when skiing on firm snow — induces large lateral bending-moments (abduction-moments) at the top (proximal end) of the tibia. Fractures in this location often extend into the surface of tibial plateau, causing damage to the menisci that are seated on the top of the tibial plateau surface. The negligent, overly-loose ISO standards for pin-bindings (wrongly called 'tech-bindings' — they are hardly 'tech') must be changed to reflect human-biomechanics, not just manufacturing tolerances that have little to do with basic human biomechanical requirements [see footnote 10]. Fat skis are great in powder or in loose-snow — but skiers should be advised that skiing on fat skis (wider than 87mm at the waist) on firm snow could end one's skiing career. Do not use fat skis on firm snow. Skiing with pin-bindings and fat skis on firm snow invites triple trouble. If you are skiing with pin-bindings (other than the Trab TR2) — no matter what the release settings are adjusted to — do not fall.
3— Settings for different skiers. The extensive biomechanical engineering work that was performed during the late 1960's through the early 1970's by several leading researchers produced data that provides tuning of release-settings for individual physiologies. Key factors that compensate for different physiologies include — weight; height; velocity (‘skier type’); age; gender; boot sole length, and recent amounts of cumulative aggressive skiing (triggering Wolfe’s Law for increased/discretionary settings).
Conclusion: tibia-related release-function of alpine ski-bindings
Integrating robust non-pre-releasing release-function into top-of-the-line alpine ski-bindings is well within the domain of Howell SkiBindings that are designed by Rick Howell. Rick Howell's education and experience in the ski-binding category is unprecedented (see 'About Us') — Howell SkiBindings reflect this background.
Further, Howell SkiBindings provide all of the positive functions that are outlined above — with less parts than other bindings. Minimal parts often leads to durability.
The release function of a ski-binding is regulated by international ski-binding standards. All ski-bindings must be certified for their compliance with the minimum international standards — ISO 9462, 9465 and 11087 — through testing by the only independent ski-binding lab in the world — by TÜV, in Munich, Germany [see footnote 9]. Even if there is no 'local rule' enforcing ski-binding certification — for example, there are no certification-enforcement rules in USA or Canada — we urge you to seek only alpine ski-bindings that are independently certified by TÜV in Germany for their function according to ISO 9462, ISO 9465 and ISO 11087 — and that meet ‘Standard Industry Practice’ for anti-pre-release and durability.
It is anticipated that Howell SkiBindings will be independently certified in Germany before being shipped into the stream of commerce.
Part 2 — ACL-Friendly Release
The low stand-height, non-pre-releasing, ACL-Friendly (sm) alpine ski-binding function that is unique to Howell SkiBindings is explained in detail in the slide-show presentation given by Rick Howell at the International Olympic Committee (IOC) conference — Prevention of Injury in Sports — on March 17, 2017 in Monte Carlo, Monaco. The presentation — ACL Integrity through Ski-Bindings — was updated and presented at the International Society for Skiing Safety (ISSS) conferences in Innsbruck, Austria on April, 2017 and in Squaw Valley, California on April, 2019 and at the International Congress on Science in Skiing (ICSS) in Voukatti, Finland in March of 2019.
How Howell SkiBindings uniquely provide ACL-Friendly skiing
First, the epidemiology and biomechanics of skiing-ACL injuries.
ACL-injuries — ~80% of which are Grade-III complete rupture — are by far the most prevalent injury in skiing: prevalence = ~21% of all skiing injuries; incidence = ~2500 mean-days-between-injury (MDBI). Higher 'incidence' is better when there are more ‘days between injuries’. MCL-injuries are the 2nd most prevalent in skiing: prevalence = ~12% of all skiing injuries; incidence = ~4200 MDBI. The incidence (MDBI) of skiing-ACL injuries is favorably improving during the past 10-years; whereas the incidence of MCL injuries is worsening during the past 8-years. The improvement in USA is most likely due to Vermont Safety Research's 'ACL Awareness Training' behavior modification programs (available on video from Vermont Safety Research); and in Sweden, the improvement is due to Maria Westin's Proprioception Training Program. Never-the-less, ACL and MCL injuries remain, by far, the most frequent injuries in skiing, today. Further, ACL injuries are severe, requiring between $20,000 to $50,000 for diagnosis, treatment and rehabilitation (not including the cost of loss work) as well as an average of ~200 days of less-than-normal athletic-function. ~50% of all skiers with Grade-III ACL ruptures develop osteoarthritis within 10-years of reconstructive surgery. Skiing-ACL injuries are both frequent (~2500 MDBI) and severe (~200 days of sub-optimal knee function).
Female ACL epidemiology
Female skiers incur ~3-times the amount of ACL injuries compared with male skiers (7-times more in basketball—though different injury-mechanisms are involved in skiing and basketball). It appears to leading orthopedic researchers that the main factors that associate with the gender differences in ACL injuries might be that females have: (1) greater valgus-angle (Q-angle); (2) sharper femoral-notch in which the ACL is positioned through the distal end of the femur; (3) a lower ratio of ACL-strength to body-weight; (4) steeper tibial-plateau; and (5) weakening of the ACL during the pre-ovulatory phase of the menstrual cycle. However, evidence-based research on causation remains scientifically unclear at this time (June, 2018) because the studies were not normalized for age. Never-the-less, female skiers are exposed to significantly greater risk of ACL-rupture compared with male skiers.
Skiing ACL injury mechanisms
The most frequent skiing-ACL injury mechanism appears to be, ‘Slip-Catch’, which is somewhat similar to ‘Phantom-Foot’. The Slip-Catch mechanism is shown at the instant of ACL-rupture in this photo:
In a Slip-Catch scenario, the outside ski 'slips' laterally in loose snow, then the edge 'bites' during the compressive-build-up of snow under the ski. This situation causes the lateral component (lateral and co-planar to the top and bottom surfaces of the ski) of the force that enters the inside-edge of the ski to be pushed at a focal-point that is located slightly behind the projected-axis of the tibia. This component of the applied load is an abduction-force — that acts over the length of the lower-leg plus the thickness of the boot-sole plus the standheight of the binding — to produce a large abduction-moment through the center of the knee and across the ACL.
Because the ski slipped while the skier's body-mass continued to load the edged-ski, the knee was forced into an exaggerated valgus-angle: this produces strain across the ACL. This scenario also generates a small torsional-torque about-the-long-axis-of-the-tibia because the skier was slightly rear-weighted — causing the lateral-component of the applied-force to enter the ski slightly behind the projected-axis of the tibia. ((The concept of stating "twisting" as a stand-alone term, is meaningless: "twisting" about what? Most of the ‘twisting’ in a Slip Catch scenario is about the femur, not the tibia.)) Clearly also, the large compressive-component of a Slip Catch event pushes the distal-end of the femur downward into the sloped surface of the tibial-plateau, further increasing strain across the ACL. In a Slip-Catch scenario, large compression-loading combines with a large abduction-moment plus a small amount of tibia-torque to produce strain across the ACL.
When a backward-bending-moment centered at the distal end of the tibia has greater magnitude than a lateral abduction-moment that is centered within the ACL, the injury mechanism converts from ‘Slip Catch’ to ‘BIAD’ (boot-induced-anterior-drawer).
All of these forces, torques, moments, valgus-angles, and tibial-plateau-angles mix together to produce large strain across the ACL, large strain across the MCL, and unevenly compresses the meniscus. Depending on the magnitude of these loads, their direction, and the kinematic movements between the distal end of the femur and the proximal end of the tibia — the ACL (and/or the MCL) will either become mildly sprained ('Grade-I'), significant-sprained ('Grade II'), or ruptured (Grade III). Meniscus can become torn.
‘Experts’ who are also orthopedic-researchers — and some who are also PhD's in mechanical engineering — have, for 4 decades, rendered a myriad of loading-scenario opinions on these various skiing-ACL injury mechanisms — only to be disputed by other groups of 'experts'.
Here's one possible — perhaps plausible — opinion on the prevalence-distribution of skiing ACL-injury-mechanisms.
This opinion about the prevalence of skiing ACL-rupture mechanisms comes from Robert J. Johnson, MD, while Director of Orthopedic Research at University of Vermont College of Medicine, Department of Orthopedics and Rehabilitation (speaking also on behalf of his research-colleagues, Jasper A. Shealy, PhD and Carl F. Ettlinger. )
Large abduction-moments are involved in the most prevalent skiing-ACL injury mechanisms
If the expert opinion by Johnson/Shealy/Ettlinger is correct — the most prevalent mechanisms that represent ~75% of all skiing-ACL injuries appear to be abduction-moment related — Phantom Foot and Slip-Catch. In these scenarios, compression-loading and tibia-torque is present, too — but noting that tibia-torque is low in magnitude — equivalent to lite children’s torsional release settings.
It’s impossible to have a ski-binding that allows the boot to release downward through the ski in response to compressive loads.
Release, in response to tiny amounts of tibia-torque, would — for adults — cause pre-release.
Release in response to BIAD-loading is possible with vertical toe release (Geze SE3) or with downward actuation of a heel-pad — but essential skiing-control loads (finishing a turn) involve partial BIAD-loading — causing a loss of edge-control and probable pre-release for Type-3 skiers. BIAD ACL-ruptures comprise ~10% of all skiing ACL-ruptures.
Backward-twisting induced ACL-ruptures can be resolved by multi-directional toe release. This mechanism also appears to cause ~10% of all skiing ACL-injuries.
By default, ski-binding release in response to large abduction-moments provides the primary way to effectively address the skiing-ACL-rupture problem.
( It’s important to note that when large compressive-loads are present, large abduction-moments are often present, too: therefore, abduction-release also addresses large compressive-loading that can cause ACL-rupture. )
Lateral-heel release can directly-respond to abduction-moments that would otherwise cause ACL-rupture — but only if (a) the magnitude of lateral-heel release is tuned to skier-size and gender; and (b) pre-release is mitigated independently of the lateral-heel release-settings.
Only Howell SkiBindings have lateral heel release that is adjustable for skier-size and gender — and — strongly mitigates pre-release without elevated settings.
Howell SkiBindings founder, Rick Howell, invested 47-years into the research and development of special lateral-heel release settings that accommodate skier size and gender to mitigate ACL-rupture. The R&D behind the special lateral-heel release-settings for skier-size and gender was presented by Rick Howell in the Spring of 2019 at ICSS-Finland and ISSS-USA. The special means-plus-function that strongly mitigates lateral-heel pre-release independently of lateral-heel release-settings is open-technology [ USPTO Patent Trial & Appeal Board Decision dated October 15, 2018; Case IRP2017-01265 involving only [emphasis added] annulled US Patent 8,955,867 B2 ].
To validate the effectiveness of specially-tuned, non-pre-releasing lateral-heel release in response to large abduction-moments that are combined with small amounts of tibia-torque — that would otherwise cause ACL-rupture — Howell SkiBindings company relies on the previously proven biomechanical analysis technique involving release-envelopes.
To do this, testing with metallic surrogates produced ACL-rupture-envelopes, which led to the development of a special abduction lever-arm analysis to scale the findings.
The ‘envelope approach’ ends 4 decades of conjecture by bringing related and proven structural engineering techniques to solve the skiing-ACL problem .
Development of an ACL-rupture envelope.
We began by benchmarking a tibia-fracture envelope. The torsional fracture-limit of an average U.S. male’s tibia is ~11.3 daNm (~11.3 ‘DIN’) [Asang, 1980] no matter where an applied-force enters the ski (though, inversely, the magnitude of an applied-force must vary as a function of where the force enters the ski in order to produce a constant level of torque about the tibia). A tibia-fracture-envelope produces a straight-line across an envelope that depicts tibia-fracture-torque as a function of where the applied-force enters a ski. See thick black line in the torque-envelope, below.
Next, we sourced data on the structural capacity of an average U.S. male’s ACL when exposed to varying combinations of abduction-moments and tibia-torques [Andriacchi, 2015]. See curved orange envelope.
In skiing, varying magnitudes of injury-producing forces enter a ski at varying positions along its length. Due to the leverage-effect of a ski, the relative-magnitude of the resultant tibia-torques and abduction-moments that flow into the human musculoskeletal system vary, depending on where forces enter the ski. Forces that enter the tip or tail of a ski have a high ratio of tibia-torque to abduction-moment. Forces that enter the ski near its center have a high ratio of abduction-moments to tibia-torques. ACL-rupture data aligns with high-ratios of abduction-moments to tibia-torques. See the thick green and red envelopes.
All of this data — tibia-torque at fracture, and combined abduction-moments and tibia-torques at ACL-rupture that vary depending on the entry-point into the ski— is too complex for ski-bindings.
To simplify the ACL-release-response, we converted all of the above torque and moment data into applied-force data that’s a function of where the applied-force enters a ski. Ski-bindings with a toe that releases laterally mixed together with a heel that releases laterally can read and react to any lateral-force that enters any point along the length of a ski. See applied-force-envelope.
Testing ski-bindings in applied-force-envelopes:
Ordinary 2-mode ski-bindings relative to the ACL
The above force-envelopes depict the release-response of an ordinary 2-mode binding while applying forces to varying points along the length of a ski and when the binding is set at DIN 6, 5 and 4. See thin envelopes: blue/6, red/5 and black/4.
Even if the binding is set at DIN-4 (thin black envelope) ACL-rupture can occur. DIN-4 is not skiable by an average U.S. male weighing ~170 pounds. Pre-release occurs. No matter how low an ordinary 2-mode binding is set to release — even at levels where pre-release can easily occur — ACL-rupture is plausible. Reducing ordinary 2-mode release-settings will not appreciably reduce ACL-injury.
(( Notice also the large margin between all of the above ordinary 2-mode binding’s release-force-envelopes and the tibia-fracture envelope. These large (good) margins explain why skiing tibia fractures barely exist with ordinary 2-mode ski-bindings. Bravo, 2-mode bindings—for tibias. 'But these envelopes critically illuminate adverse ski-binding function with respect to the ACL. ))
Through the use of ‘envelope analysis’ — where all plausible injury-mechanisms are tested on ordinary 2-mode bindings — the skiing ACL problem is exposed.
Now, new Howell SkiBindings — with additional non-pre-releasing lateral-heel release — produce a release-response that is below ACL-rupture. See thin black release-envelope, below.
Modes of release effect ACL integrity
How do these two different types of bindings — 2-mode versus 3-mode — produce different release-envelopes?
Howell SkiBindings uniquely produce a fundamentally different release-response in the presence of applied abduction forces that enter the back half of the ski — below theoretical ACL-rupture — through specially-tuned lateral heel release.
Settings for lateral heel release
Recommended lateral-heel release settings — only for Howell SkiBindings — are based on the unique anti-pre-release function of each mode of release within Howell SkiBindings.
Each time the ski flexes — even slightly — the lateral heel release mechanism in Howell SkiBindings powerfully forces the heel of the boot to re-center — unless the above-outlined critical ACL-injury-limit is approached (minus a margin) ... at which point the lateral heel release mechanism provides elastic re-centering to dissipate an innocuous load OR the mechanism provides full release when a potential ACL-injury load further approaches the critical limit.
For convenience, we have indexed the visual indicator on our lateral-heel release adjustment mechanism with a numbering-system as follows:
1— Lateral-heel release-force supplied by Howell SkiBindings for any given visual indicator number is not the same lateral force that is supplied by the same visual indicator number in the toe. It is not the same force supplied by other bindings with lateral-heel release (e.g. - not the same lateral-heel release-force as ‘Kingpin’).
2— Recommended lateral-heel release-settings include an additional correction factor for gender: females have a lower lateral-heel release-setting compared with males (based, in-part, on the ‘Epidemiology’ and ‘Biomechanics’ that are outlined above. For more detailed information, please contact Howell SkiBindings).
3— For skiers who select settings above ‘8’ for the lateral-toe release setting or for the forward-heel release release setting — the lateral-heel release-setting should remain at ‘8’. If a skier prefers to waive ACL-friendly skiing, the top of the lateral-heel release-adjustment scale provides a fully ‘BLOCKED’ setting.
The derivation of our recommended lateral-heel release-settings is based on 47-years of research and development that was presented at ICSS-Finland and ISSS-USA in the Spring of 2019.
Additionally, the low 17mm standheight in patented Howell SkiBindings reduces cumulative strain across the ACL, MCL and meniscus.
And, finally, all 3-modes of release in Howell SkiBindings are functionally decoupled from edge-control. Intentionally putting a ski up on edge on rippled blue-ice — fully loaded — does not actuate the lateral-heel release-mechanism in Howell SkiBindings.
In these ways, Howell SkiBindings provides an extraordinary skiing experience.
Pre-order ( $80 ) by Reservation-Deposit:
Howell 800 Venus — Loaded with ACL-Friendly features for lite & strong women. DIN 2.5—9 $800
Howell 880 Pro — The core of the Line. ACL friendly. Without pre-release. DIN 5—15 $800
Howell 888 Max — CAUTION: EXTREME SKIERS & RACERS ONLY. DIN 8—20 $1200
Pre-orders placed now receive FREE shipping in October, 2020 — and 30% OFF the base price when the net amount is invoiced in October, 2020.
FLAT-OUT SKIING CONFIDENCE.
It was inevitable.
PO Box 1274 • Stowe, Vermont 05672 USA
1.802.793.4849 • email@example.com • www.howellskibindings.com
Footnote 1: The engineering term, "moment" is applied to structures (such as the tibia or the ACL) when forces and lever-arms cause the structure to 'bend' about its long axis. The related term, "torque" is applied to a structure (such as the tibia or ACL) when forces and lever-arms cause the structure to twist about its long axis. In both cases — 'moment', or 'torque' — the simple engineering equation that applies to the phenomena is, "T = f X r", where "T" can be either 'torque' or 'moment'; "f" is the applied-'force'; and "r" is the 'distance' between the applied-'force' and the point at which the 'torque' or the 'moment' is being resolved, measured or analyzed. In the case of a 'moment', one could select any point along the length of a column (tibia or ACL) to analyze the instant bending-'moment' at that point. When the term 'forward bending-moment' is utilized with ski-bindings — it is intended to mean 'forward release' — but the phenomena involves the bending of the tibia, so the correct term is 'forward bending-moment'. (The term 'forward lean release' is an incorrect misnomer: 'forward lean' is the angle of a boot's upper shaft relative to the ski. The person who coined the term, 'forward lean release' is not much of a skier and does not really understand skiing. Besides, Spademan — when it was fully-developed just before its demise — could not really release in the forward-shear direction, so there is no longer a need to differentiate between 'forward-lean' and just plain 'forward'.)
Footnote 2: The lay-term 'load' means — 'torques', 'bending-moments', ‘abduction-moments’, ‘edging-moments’ or 'forces'.
Footnote 3: Biomechanical tibia-fracture data: Skiing Safety II; Editor, Jose Figuras, MD; 1978, ISBN 0-8391-1209-2.
Footnote 4: Current anthropometric data: U.S. National Highway Traffic Safety Administration, Research & Data, 2017; and The Measure of Man and Woman: Human Factors in Design, Alvin Tilley, Henry Dreyfuss, ISBN-10: 0471099554.
Footnote 5: 'Ski Binding Settings Based on Anthropometric and Biomechanical Data'; Malcolm Pope, DrMedSci, PhD; Robert Johnson, MD; Human Factors, Vol.18, pp 27-32, 1976.
Footnote 6: 'Discretionary Settings' are allowed by international standard DIN/ISO 8061.
Footnote 7: 'The Biomechanics of Contemporary Ski Bindings'; Journal of Safety Research, Vol. 4, pp 160-171, 1972, Eugene Bahniuk; 'Analytical Studies of the Biomechanics of Contemporary Ski Bindings', Mechanics and Sports, The American Society of Mechanical Engineers, pp 221-236, 1975, Eugene Bahniuk; 'Theoretical Estimation of Binding Release Values', Orthopaedic Clinics of North America, Vol. 7, No. 1, pp 117-126, 1976, Eugene Bahniuk; and 'A Method for the Testing and Analysis of Alpine Ski Bindings', Journal of Safety Research, Vol 12, No. 1, pp 4-12, 1980, Eugene Bahniuk et al.
Footnote 8: When the release setting is changed upward or downward, the entire uniquely-shaped release-envelope of any given ski-binding design, shifts upward or downward: the shape of each unique ski-binding's release-envelope does not change. This means that a release setting prescribes only one small aspect of the overall release function. This issue is important to understand and to recognize in terms of a key limitation of all release settings for all bindings.
Footnote 9: Certification of compliance with ISO 9462 ('release characteristics' and some functions pertaining to 'retention'); ISO 9465 (lateral toe retention during dynamic impact); and ISO 11087 (ski-brake function) — by an independent lab — is mandatory in Germany, Austria, and Switzerland. In Switzerland, non-certified alpine ski-bindings are removed from retail ski shops by the Swiss-BfU.
Footnote 10: References: (1) Dominik Heim, MD; SITEMSH-Japan, 2016. (2) Zorko; Nemec; Matjacic; Olensek; Alpine Skiing Simulations Prove Ski Waist-Width Influences Knee Joint Kinematics; ISSS-Innsbruck, Austria, 2017. (3) Stenroos; Pakarinen; Jalkanen; Mälkiä; Handolin; Tibial Fractures in Alpine Skiing and Snowboarding in Finland: A Retrospective Study on Fracture Types and Injury Mechanisms in 363 patients; Scand J Surg Off Organ Finn Surg Soc Scand Surg Soc., Sept 2015, doi:10.1177/1457496915607410. (4) Improved Short Term Outcomes in Tibial Plateau Fractures of Snow Sports Injuries Treated with Immediate Open Reduction Internal Fixation; Janes, MD; Leonard, MSPH; Phillips, PA-C; Salottolo, MPH; Abbott, MD, Bar-Or, MD; ISSS-Innsbruck, Austria, 2017.