# EDGE CHANGE INERTIA + ROCKER ROTATION INERTIA

As I was in the process of writing this post, a FaceBook group on skiing posted a link to an article From PSIA: Examining Transitions. The article is based on a presentation last fall by US Ski Team Head Men’s Coach, Sasha Rearick, in which he shed new light on transitions (1.).  While Rearick did shed light on some events associated with transitions, as with previous efforts by others on this subject, Rearick failed to shed light on the mechanics and physics associated with edge change.

As I explained in my last post, transferring the weight from the outside foot and ski of a turn to the inside foot and ski in the transition phase sets in motion what I call the Eversion/Internal Rotation Cascade that rotates the base of the ski into a transient moment of full contact with the surface of the snow between changing to the new (downhill) edge.

At the start of the transition leading up to ski flat between edge change, the center of pressure (COP) of the weight of the body applied by the sole of the inside foot will be under the heel where it is aligned on the proximate center of the ski. In this configuration, the force applied to the ski by the skier is working with gravity to rotate the ski.

The post left off by showing how rotational inertia will tend to make the ski continue rotating about the uphill edge past ski flat and penetrate into the snow surface on its downhill aspect as shown in the graphic below.

Rotational inertia will tend to make the inside edge of the new outside ski automatically rotate into the turn except for the fact that the force FW applied by the skier is on the wrong side of the new edge.

The graphic below has a dashed red reference that is parallel with the snow surface.

If the force FW applied by the skier is still aligned on the transverse center of the ski, it act will act to oppose edge change as shown in the graphic below. When the axis of rotation of the body of the ski changes with a change in edges, the transverse aspect of the base of the ski and the platform under the skier’s foot will tend to accelerate into an eversion translation. But this can only happen if the associated biomechanics are not interfered with by the structures of the ski boot.

The graphic below shows the change in the mechanics of rotation associated with edge change.

At the start of the transition, movement of the mass of the skier’s upper body is in phase with the downhill rotation of the ski and the force FW applied to it. But when the ski changes pivots at edge change and the mass of the skier continues to move downhill, the force FW applied to the ski will tend to rotate it back to ski flat; i.e out of the turn, unless the point of application of force FW changes during ski flat as shown in the graphic below and COM of the skier is aligned with force FW.

………. the angle between the platform and force you apply to it, the platform angle, must be 90 degrees or smaller.  – page 19, The Ski’s Platform Angle, Ultimate skiing; Le Master

The shift in center of pressure from the heel to the ball of the foot in a turn sequence seen in pressure studies of expert skiers is well documented (2., 3., 4). What the studies are really confirming is the use by expert skiers of the Two Phase Second Rocker mechanism to rock (tip) the outside ski on edge and control the edge angle during the load phase of a turn sequence.

Since the limit of the position of the application of force by the foot in relation to the inside edge of the outside ski is the center of the ball of the foot the effect of ski width underfoot and stand height should be obvious. Both rotational inertia and torque will increase as the width of a ski underfoot (profile width) is reduced and stand height increased. When Ligey says he creates pressure, he is creating far more than just pressure.

While LeMaster appears to recognize the importance of a platform angle less than 90° for edge control and, to some degree, the effect of stand height, the explanation offered for superior edging is that this can be attributed to waist width and stand height making skis more like ice skates.In my next post, I will discuss the role of Turntable Rotation in setting up a platform under the body of the outside ski for a skier to stand and balance on while maintaining edge angle.

1. http://eliteskiing.com/2017/03/31/from-psia-examining-transitions/
2. WHAT THE TWO HIGH PRESSURE COPS IN THE UNIVERSITY OF OTTAWA STUDIES MEAN – https://wp.me/p3vZhu-1fV
3. IMPLICATIONS OF THE UNIVERSITY OF OTTAWA PRESSURE STUDIES –https://wp.me/p3vZhu-1e2
4. AN INDEPENDENT STUDY IN SUPPORT OF THE UNIVERSITY OF OTTAWA FINDINGS – https://wp.me/p3vZhu-1gR

# THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: THE TURNTABLE EFFECT

Neither the Two Phase Second Rocker (heel to ball of foot rocker) described in THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: HEEL/FOREFOOT ROCKER (1.) or the Rotating Turntable Effect described in THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: THE ROCKER/TURNTABLE EFFECT (2.) are new. They have been the trademark technique of the world’s best skiers for decades. But the ability to engage the associated mechanics and biomechanics requires what amounts to a perfect storm that typically occurs early in the development of a young skier. More than raw athletic talent, discipline and dedication, the ski boot appears to be the critical factor that determines who acquires the ability to engage these effects.

In working with skiers and racers who are gifted natural athletes, it has been my consistent finding that a change in ski boots that compromises neuromuscular function will result in the body adopting compensatory mechanisms that can reduce competence on skis to survival reactions. Given sufficient time, the survival mechanism will become imprinted until a point is reached where it is accepted as normal by the body. Even after the cause is corrected, it can take years of retraining to erase and replace survival motor patterns. A good example of this is what happened to Mikaela Shiffrin at the start of the 2014-2015 World Cup after changes were made to her boots in the fall of 2014. Fortunately, she was able to revert to her previous boots over Christmas and quickly restore her former competitive competence.

Four synergistic mechanisms associated with the mechanics of edge change result in the creation of a platform under the outside ski that a skier can stand and balance on. These are:

1. The Two Phase Second Rocker (heel to ball of foot rocker) Mechanism
2. Impulse rocker loading that occurs at edge change
3. The Over-Center mechanism, and
4. Open and Closed Chain Whole Leg Rotation; The Rotating Turntable Effect.

The most critical and seemingly least appreciated and understood mechanism in skiing is the mechanics and biomechanics of whole leg rotation.

LeMaster recognized the role of whole leg rotation in skiing in his book Ultimate Skiing when he stated under Twisting Actions (p 13) that torques play important roles in turning skis and holding them on edge. In Chapter 7, Turning the Skis (p 107), LeMaster states, Rotating the leg inward generally rolls the ski on its edge, too, combining the increase in the edge and platform angles—often a desirable combination while acknowledging that leg rotation is powerful and can produce large torques through the whole turn. But LeMaster does not describe the mechanics associated with whole leg rotation in this context.

### The Center of Rotation

Whole leg rotational force is applied to the femur primarily by the gluteus medius.

The most important source of rotational power with which to apply torque to the footwear (ski boot) is the adductor/rotator muscle groups of the hip joint. – US Patent 5,265,350 MacPhail

Rotation of the femur is transferred through the tibia where it is applied through its lower or distal aspect to the talus that forms the ankle joint with the tibia.

The graphic below shows a skeleton of the foot aligned on a fixed reference axis (dashed line).The graphic below shows the same skeleton of the foot rotated 15° medially (towards the center of the body) against the fixed reference axis (dashed line).

The graphic below shows the relative displacement of the heel and forefoot in relation to the fixed reference axis (dashed line).

The graphic below compares the displacements of the heel and limit of the forefoot at the end of the second toe with horizontal lines in the center of the graphic. The lines show that the end of the second toe displaces almost 4 times as much as the rearmost end of the center of the heel during whole leg rotation of the foot. Hence the advice in my post, THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: PRESS AND POINT THE BIG TOE (3.), to point the big toe in the direction you want to go.

### Open Chain Rotation vs Closed Chain Rotation

• Open Chain Rotation – occurs when the foot can rotate in the horizontal plane in conjunction with the rotation of the whole leg from pelvis. In ski technique, this is referred to as steering.
• Closed Chain Rotation – occurs when the foot is fixed on its long axis and whole leg rotational force is applied to the foot from pelvis.

Open Chain whole leg rotation acting about the axis of the ankle joint in combination with a Two Phase Second Rocker induced Over Centre mechanism are prerequisites to the application of Closed Chain Rotation. The emerging profile created by the steering angle of the outside ski as it crosses the fall line below a gate yields important clues as to the technique of a racer.

In my next post, I will discuss Closed Chain Rotation applied to the outside ski in a turn and the transfer path of torques applied to the foot by the leg through the boot-binding interface to the ski.

# SYNERGY: A MULTI-DISCIPLINARY APPROACH TO SKIING

### Introduction

In 1991, when I designed the research vehicle called the Birdcage and sometimes simply The Gadget, with Alex Sochaniwskyj, P. Eng., a biomedical engineer, we employed a multi-disciplinary approach; one that encompassed as many factors as possible. In his letter of support for my nomination for the Gold Medal in Applied Science and Engineering in 1995 British Columbia Science & Engineering Awards, Alex said:

During 1991 and 1992, I had the opportunity of working with David MacPhail in the realization and testing of conceptually innovative sports footwear. Design of this type requires, knowledge, understanding and experience in a combination of disciplines including anatomy, physiology, biomechanics, sports dynamics, physical mechanics and design. David MacPhail exhibited this unique combination throughout all aspects of the project, and continues to research and explore developments in: influences of footwear on the kinematics and kinetics of human movement; the design of athletic footwear; and the etiology, occurence, frequency and prevention of athletic injuries.

Alex Sochaniwskyj, P. Eng.

### Synergy

In 2000, I formed a partnership with Joanne Younker, a CSIA Level IV ski pro and coach at WhistlerBlackcomb and Sophie Cox, a podiatrist from London who was trained by Novel Germany in the use of their Pedar insole pressure analysis system. Our collective efforts and expertise formed a complimentary multi-disciplinary core that we augmented with other expertise such as physiotherapy, chiropractic and myofascial release therapy.

Originally published in Whistler’s Pique Newsmagazine on February 18, 2000 under the title DIGITAL SALVATION FOR THE SOLE [BACK TO THE FUTURE]

“Any sufficiently advanced technology is indistinguishable from magic.”  – Clarke’s Third Law

Conspicuous hardly begins to describe what I was feeling.  In the early morning rush of skiers grabbing a quick caffeine rush at the Wizard Grill, amid tables full of Ski School twinks waiting to see whether they were going to have any work for the day, an attractive woman was carefully stringing computer cables up the inside legs of my ski pants.  Things like that draw attention even at the base of Blackcomb on a Monday morning.

One end of the cables were attached to pressure sensing insoles in my ski boots, the other to a data recording box I was trying to figure out exactly were to attach.  About the size of an epic Michener paperback, it was just too big to slip into any of my pockets.  Finally clipped to the waist of my pants, it was, in turn, coupled to a high-powered flash unit strapped to my arm, both of which were fired by a button left dangling pretty much nowhere.

Robocop.  I couldn’t get the image out of my head, although at least one person who asked what all the hardware was about accepted my answer that it was a control mechanism to power my artificial leg.

David MacPhail grabbed the digital video camera and we headed up Blackcomb to take some measurements.  Dave — who I’d been working with to document some background on the Rise boot he’s been developing — had only recently launched Synergy Sports Consultants.

I wasn’t clear where exactly he was taking me or what we were going to accomplish, but a more willing guinea pig would have been hard to find.  In the nether world of ski theory, and more particularly in the areas of skiing biomechanics and modeling, Dave MacPhail is riding the cutting edge.  His work with National Team skiers and his understanding of exactly happens to the human body when it straps on a pair of skis has brought him an international reputation as an authority in the field.

On a clear slope under the Solar Coaster, Dave skied ahead to set up the video shot.  Sophie — who’d wired me up — rechecked the cable connections, set a baseline measurement for each of my unloaded feet and told me to point the flash unit down the hill at the camera.

As they signaled their readiness to each other, Sophie fired the flash and told me to ski down toward Dave.

Making my best ski school turns, I skied for the camera.  We repeated the process a few times and then we went back down to the Daylodge to…well, I wasn’t sure to do exactly what.

What, turned out to be mind blowing.  The unit strapped to my waist was a Pedar foot pressure data recorder from the Novel company of Munich, a techy little piece of equipment that, until last year, was the size of a small desk.  On a PCMCIA flash card, the unit was capable of recording about 10 minutes worth of data.  Fed by 80 pressure sensors arrayed throughout the insoles in my boots that each took 50 measurements per second, the Pedar tracked pressure across time as my feet worked to move me like a skier.

Downloaded onto a laptop computer and run through the company’s software, the data could be displayed as images of my left and right foot, colour-coded across the sensing mechanisms to display the changes in foot pressure as I made turns.  With lower pressure readings showing up as black squares and higher pressure lighting up bright pink, the readout was a moving kaleidoscope of colour as it played back my runs down the mountain.

On each colourful foot profile, a small dot traced a red line showing my centre of pressure at any moment in time.  A good skier using foot pressure the way they’re supposed to, would, over the course of a run, track a red line from the ball of their foot back toward their heel.  The track would be true and relatively straight with few variations.  That’s what the tracing on my right foot looked like.  The track of pressure of my left foot looked like someone who had never seen an Etch-A-Sketch grabbed both knobs and started twisting them randomly.

The difficulties showing up in my left foot readout were verified when Sophie explained the graphic display at the top of the screen.  “This line graph shows change in pressure over time for each foot.  When you make a good turn, like you’re doing with your right foot, the graph of pressure shoots up dramatically at the start of the turn, drops down slightly to a plateau, then falls away as you unweight the foot at the beginning of the next turn.  Your left foot comes on very gradually.  Something’s blocking your foot function,” she explained.

The final diagnostic piece of the puzzle — at least as far as the technology end of things went —was put in place when Sophie downloaded the images from the digital video camera and synchronized them with the Pedar display.  There I was, making graceful turns and there was the readout of what my feet were doing — or not doing, as it turned out.

“Neat,” I said.  “Now what?”
“Now you find out what Synergy is all about,” said Dave.

Synergy — small “s” — is about joint action of different substances producing an effect greater than the sum of the effects of all the substances acting separately.

The whole being greater than the sum of the parts.

In a theological context, synergy is a doctrine that human effort cooperates with divine grace in the salvation of the soul.  I’ve often thought of skiing as a salvation of the frozen Canadian soul and certainly a day in the high alpine making perfect turns in all conditions is as close to divine grace as most of us will ever come.  But it was the more secular meaning of the word Dave had in mind in naming the company.

“The whole concept of Synergy probably came into my mind 25 years ago.  I started thinking about something called bio-integration, bringing people with different important skills together to work holistically on making your body work right.  Five years ago, we couldn’t have launched Synergy because the technology wasn’t quite there.  We needed more sophisticated software and I could see the time coming closer to when we’d reach a point where a lot of things in athletics that are mysteries now were going to be revealed by being able to plug in sensors at key points of interface.  Now, we’re starting to get there.”

But data is just data without something to make it sing.  And that’s where the principals of Synergy begin to make the concept work.  Joanne Younker is Synergy’s president. She’s been working with Dave for 12 years on both the Rise boot and putting together a biomechanical model of how people ski, how joints and muscles and nerves and bones work together to overcome our natural tendency to fall down when the earth starts to slide out from under our feet at an accelerating rate.

Joanne’s a level IV CSIA instructor and a level II CSCF coach and a personal trainer when she’s not on skis.

Sophie Cox and Joanne Younker

She’s been a keen skier since she was fourteen and a student of kinaesthetics since 1989 when she blew her back out squatting improperly in the weight room, an injury leading to temporarily paralysis and a burning desire understand how her body works.

“Working with David, and studying the biomechanics of skiing, I can look at someone skiing and understand what they’re doing wrong and, more importantly, probably why they’re doing it.  That is, what muscles aren’t functioning right or what functions are blocked.  Working with this technology, I can validate my diagnosis with hard data.”

Using a set of dry-land kinaesthetic exercises, Joanne led me through a session designed to help me experience the “feel” of having the right muscles firing and applying pressure with the correct area of my feet.  Once I’d managed to do these correctly, she had me stand on the Pedar’s insoles outside my ski boots.  Connected to the computer, they gave me a real time display of where, in turn, I was applying pressure with each foot. Running me through the exercises again, I could use the display to associate that “feel” with a visual representation of correct pressuring.  There was no guesswork.  When I lit up the right area of the pressure pads, I was having my feet do exactly what they should do to initiate a good turn.

The final step of the exercises was to slip the insoles back into my ski boots and repeat the exercises again.  Within the confines of my boots, I could watch as I pressured the ball of my foot and got my bulk into the right plane of alignment.  I was surprised — as is virtually everyone else who has gone through this exercise — at how far forward I really needed to bring my centre of mass to consistently apply pressure where needed.

All of this might have taken a lot longer to happen if the third member of the Synergy team hadn’t walked into town by accident.  Sophie Cox finished her B.Sc. at the University of Brighton School of Podiatry in, England, in the summer of 1998 and was working in a Podiatry clinic in London.  Her mother brought home a bottle of Whistler spring water  — the same water that gets flushed down toilets in Function Junction, ironically — and she was taken with the idea of goofing off for a year in Whistler.  After some web surfing, she decided to take a job as a bootfitter at Can-Ski and really learn how to ski and party, Whistler style.

A colleague in Boston mentioned the groundbreaking work Dave had been doing in biomechanics and planes of movement associated with skiing to her and she attended a presentation Dave made last March to the Congress of the Canadian Sports Medicine Association.  “After Sophie met David and explained what she’d been doing with the Pedar, he was really excited.  He called me up and said, ‘I’ve met the third person!’ and we went from there,” Joanne explained.

After a summer back in England working , Sophie returned this fall to work with David and Joanne on the biomechanics of skiing and help launch Synergy.  What she brings to the table, in addition to the technology, is an in-depth understanding of the structures and movement of the foot and ankle joints and a wealth of knowledge in diagnosing problems related to feet and lower limbs.

“I look at a skier’s mechanics, what they can and can’t do, and try to decipher why they can’t do it.  Sometimes it’s bad motor skills and that’s Joanne’s part.  But if she’s trying to teach them a skill and they just don’t have the biomechanical capability to do it, that’s where I come in.  I can determine the physiological problem and refer them on to a physio or bootfitter or local podiatrist.”

“The only way of discovering the limits of the possible is to venture a little way past them into the impossible.”

– Clarke’s Second Law

For me, the proof of what Synergy was offering was back out on the slopes.  I practiced and visualized what Joanne had shown me, let Sophie make a few modifications to my left footbed and got wired up again a few days later.  Back at the computer after two or three runs, I sat in rapt amazement at the difference.

On the Pedar’s readout, the front of my feet were lighting up at the initiation of each turn.  The tracking line of the centre of force had moved inward — indicating a much stronger pronation, getting the ski on its edge — and my left trace looked like something made by a functioning foot instead of a peg leg.

I know what you’re thinking; almost anyone can help me be a better skier.  That’s like crowing about doubling your money when you only have fifty cents to start with.  But what about good skiers?  What can all this do for them?
Funny you should ask.

In the fall of 1991, during dry-land training in Banff, Rob Boyd blew a disc at the L-5, S-1 joint in his back.  An ensuing laminectomy restricted his mobility and left some nerve damage on his right side— although not enough to keep him off the podium from time to time for the next six years.  “I learned to compensate using different muscle patterns,” he said.

Three years off the World Cup Circuit now, and away from the daily coaching, Rob wasn’t happy with the way he was skiing this season, nor was he happy with his finishes in the early Ford Pro Series downhill races.  “I saw Jim DeMarco, M.D. wired up to this thing one day and started thinking maybe Dave — who had done a lot of boot work for Rob in the past — could do some testing on me and help me find some answers.”

Sophie and Joanne ran Rob through a gait test, using the pressure pads inside his running shoes while he walked the treadmill at Meadow Park.  “What we saw,” Sophie related, “was Rob had some blockage in the way his foot was functioning.  He wasn’t pushing off the ball of his foot with any force at all but compensating through other muscle patterns.”

“Right away, from what we saw on the data, my suspicions were confirmed that my right side wasn’t working well,” Rob added.

What they saw when Rob was hooked up to the Pedar for the first time on the slopes was even more surprising.  His heels lit up like a Christmas tree and he was almost never pressuring the front of his boot.  His left turns were strong and crisp but his right turns were nowhere near the same intensity.  “Yeah, that was surprising to see.  It felt like I was skiing alright and using the balls of my feet but I wasn’t even close,” Rob said.

Dave went to work on Rob’s boots, Sophie made some modifications to his footbeds and Joanne got him started on a series of patterning exercises and visualization techniques.  “I could really feel the difference when I started concentrating on using my foot more.  That and the changes in my boot environment made a big difference.  I could feel it right away at Sugarbush (Vermont).  My skis were gliding on the flats; just floating,” Rob said.  He could also see the results in his times: second on his first run and fourth on his second.

Sophie Cox, making adjustments to the Pedar system on Whistler’s Rob Boyd.

Rob Boyd on the Pedar screen.

“The next step will be to set Rob up with a physiotherapy regimen with Allison MacLean,” Joanne said.

And that’s where the remaining synergy of Synergy comes into play.  The company’s goal is to actively work with bootfitters, physiotherapists, chiropractors and other specialists in the community who can treat the whole person.

Allison is just beginning to work with the Synergy people and is excited about the “integrated approach” they’re trying to bring to problem solving.  “The data gathering and testing they’re doing is interesting,” she told me.  “It’s hard sometimes to know exactly what’s not functioning in the case of lower limb injuries and whether what your treatment is as effective as it could be.  When they send someone to me, we’ve got a pre-treatment set of data we can compare to post-treatment performance to really know whether what we’re doing is effective.”

“Every other person you bring into this adds something to the mix and produces even more beneficial results,” Dave explained.  “Sophie and Joanne and I, working together, have a much greater impact than any one of us could have on our own.  That’s the genesis behind Synergy.  But we want to bring the best resources we can to bear and make it so everybody looks like a hero.”

This obviously includes some of the best bootfitters in town.  George McConkey is sold on the idea.  “What Synergy is doing validates a lot of my own ideas about foot function and bootfitting,” he said.  “I still believe 99% of most peoples’ problems are in their boot and with any luck, what we’re starting to see in the way of data coming out of this will get the manufacturers interested in designing boots that work.”

Scott Humby, one of the owners of Fanatyk Co., isn’t so sure what’s going on is going to shake up the industry, but he sees potential benefit.  “I think what they’re doing can help you by really proving what’s going on in your boots.  If it make you feel better about your skiing; you’ll ski better.  If, as bootfitters, we’ve done all we can for someone and they’re still struggling, we’ll definitely send them on to Synergy because there may be something we’re just not seeing.  There’s a huge benefit in being able to refer someone on to a team of specialists.”

It seems axiomatic that what Synergy is doing is the way sports will go in the future.

The advances in sports in the last 25 years have largely come about because of a refinement in coaching techniques and technological innovations in equipment.  But most of what’s being done on the coaching front still relies on what a coach can see and how he or she interprets that visual data.  The advances in coaching and teaching in the next 25 years will probably be realized through the application of measurement technologies only now being brought into the field.

Some people in town and on the mountains think what Dave’s up to is another bit of high-tech quackery, other’s are true believers.  But whether coaches and instructors and others who guide athletes embrace the kinds of tools is probably more a matter of when, not if.  Elite athletes will demand it; the wired generation coming up will assume its presence. And guys like me who just want to get better and shorten the distance between muscle pattern and muscle memory will embrace it the same way we embraced those shapely new skis we can’t live without.

In the meantime, Arthur C. Clarke’s Law of Revolutionary Ideas is probably apropos:

Every revolutionary idea — in science, politics, art or whatever — evokes three stages of reaction. They may be summed up by the three phrases:

1. “It is completely impossible — don’t waste my time.”

2. “It is possible, but it is not worth doing.”

3. “I said it was a good idea all along.”

#### Watch out for number three.

author- J.D. Maxwell

reprinted with the permission of Whistler Piquenewsmagazine – published on February 18, 2000

### Epitaph

For a brief moment in history, skiing stepped out of the shadows of the dark ages into the brilliant sunlight of knowledge. For a brief moment, it was all about the skier. For a brief moment, the skier counted. Then, as if blinded by the light, skiing slipped back into the comfort of orthodoxy and uninformed opinion where eminence trumps evidence.

# STANCE HACK: TUNE UP YOUR FEET

### Biohacking Your Body with Barefoot Science

“…… hacking” or finding a way to more efficiently manipulate human biology.  This can include areas of sleep, nutrition, mental health, strength, recovery. (1)
– Dr. Emily Splichal – Evidence Based Fitness Academy

Last ski season, I developed some simple cues or hacks to help skiers and racers quickly find the body position and joint angles required to create the pressure under the outside foot with which to impulse load the outside ski and establish a platform on which to stand and balance on through the turn phase –  THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: IMPULSE LOADING

The primary source of information that helped me develop these cues are the exercises developed by Dr. Emily Splichal. Her exercises also helped me to appreciate the extent to which traditional supportive footwear with raised heels and cushioned soles has damaged my feet and deadened the small nerves responsible for maintaining upright balance and the ability to initiate precise movement. Since implementing Dr. Splichal’s evidence based science, I am not only skiing at a level beyond what I considered possible, I am starting to walk naturally for the first time in my life.

The information contained in Dr. Splichal’s videos will challenge everything you know or thought you knew about what we have been conditioned to believe about our feet and the footwear we encase them in. Contrary to what we have been told, cushioning under the feet does not reduce impact forces on the lower limbs and protect them. Instead, it actually increases impact forces while slowing what Dr. Splichal refers to as the time to stabilization; the time required to stabilize, stiffen and maximally protect the joints of lower limb from impact damage – THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: TIMING OF EDGE CHANGE

### The Best Surfaces to Train On

A good place to start is to learn which surfaces are best to train on. Again, while it may seem logical and intuitive that surfaces with cushioning are best because they will protect the body from shocks, studies show the exact opposite to be true. Over time, support and cushioning in shoes can diminish the sensitivity of the rich small nerve matrix in the feet that acts as a neural mapping system for balance and movement. In her YouTube video, Best Surfaces to Train On ), Dr. Splichal discusses the effects of different surfaces on plantar small nerve proprioception and explains how barefoot training is a form of small nerve proprioceptive training designed to activate the plantar foot. Balance training is best done barefoot.

### The Power of Plantar Proprioceptors

Watching Dr, Splichal’s webinar presentation Understanding Surface Science: The Power of Plantar Proprioceptors – https://youtu.be/t5AU-noqMFg will further your appreciation of the power of plantar proprioception.

### First Stance Hack – Plantar Foot Release for Optimal Foot Function

Dr. Splichal’s 6 Minute Plantar Foot Release for Optimal Foot Function – https://youtu.be/zyrKgFwsppI will dramatically improve foot function.
Dr Splichal explains how to use RAD rollers (golf ball or other firm balls will also work) to optimize foot function by releasing tissues in the plantar foot by applying pressure to the 6 areas shown in the graphic below.
Dr. Splichal advises to focus on using a pin and hold technique  (not rolling the foot on the balls) to apply pressure to these 6 spots on each foot holding for about 20 seconds on each spot with each of the three different sized rounds for a total time of about 6 minutes. The foot release should be done 2 times and day and prior to each training session.
In my next post I will talk about the second Stance Hack: Pressing Down on the Big Toe to Impulse Load the Ski and Power the Turn

1.  https://barefootstrongblog.com/2017/04/28/biohacking-your-body-with-barefoot-training/

# OFF SEASON POST ACTIVITY

With ski season coming to an end in many parts of the world, I am going to start posting on what I have learned over the past ski season and changes that can be made to components such as the boot board (aka Zeppa) to improve performance and why how these changes work. I am also going to post on the implications on skiing of recent studies as well as the application and impact of technologies such as CARV and Notch. If these products become available soon enough, I plan to some testing before next ski season so I can write posts on how these technologies can be used to improve ski technique and technical analysis as well as identify problems caused by ski boots.

For the time being, I have decided to hold off on discussing the rocker impulse loading mechanism of the mechanics of balance on the outside ski because limitations imposed by the ski boot prevent the majority of skiers from generating the high transient impulse load within the 2 millisecond window that occurs during roll over through ski flat during edge change (see THE MECHANICS OF BALANCE ON THE OUTSIDE SKI: TIMING OF EDGE CHANGE) that is required to engage the mechanism that enables a skier to balance on the outside ski.

For academics, researchers and others with an interest in the science aspect of the design of ski equipment and the formulation of ski technique, I will be posting studies that have application to both.

# SKIING BIOMECHANICS EXPLAINED BY DAVID MACPHAIL – EPICSKI 2002

While going through my files, I found an article that Joan Rostad compiled and edited in September 2006 from my writings to the Ski Balance forum that spun off from EpicSki in 2002. Since it no longer appears to be available on the internet, I have decided to put up it as a post.

It was around 2002, after someone introduced me to the EpicSki forum, that I connected with Joan Rostad. Joan was a Professional Ski Instructors of America (PSIA) executive vice president and served as a board member from 1989 until 2002. She was a writer, editor and publisher of EpicSki, a popular skiing website. Joan and I shared a common passion for skiing and a commitment to making a contribution to the advancement and enjoyment of the sport.

By 2002, the Birdcage/Rise project that started in 1991 to attempt to bring a ski boot to market based on principles of anatomy had become insolvent. A more recent attempt to introduce pressure analysis to skiing to diagnose boot problems as the cause of technical faults had stalled. Although I was optimistic that my ski boot design would become a reality after the unprecedented success of the Birdcage experiments that validated my hypothesis of the mechanism by which the world’s best skiers were able to truly balance on their outside ski, my optimism turned out to be short-lived. The project suffered one setback after another, eventually becoming insolvent in 2000.

### Newton’s Laws and Product Marketing

Shortly after the successful Birdcage studies, a friend who worked in marketing told me that while I had gotten the right answer in terms of what a ski boot should be, it was the wrong answer for the current players who were seeing a growing revenue stream from the wrong answer. He told me to expect pushback. He turned out to be right

Like Newton’s body in motion that continues in motion until acted on by an external force, a successful product  acquires economic inertia that resists new thinking. This issue aside, accepting that my ski boot was founded on the right principles would constitute a tacit admission that current ski boots were based on the wrong principles. This is not a good marketing story.

### In Honor of Joan Rostad

By 2002, Joan Rostad (aka nolo in EpicSki), myself and others were witnessing a growing erosion of the passion that had long been the essence of skiing as the increasing corporatization shifted attention away from skiing and the skier to the skier’s wallet. Rostad, myself and others were attempting to create a common platform in EpicSki  that would unite those who were facing an uphill battle in their attempts to retain a semblance of the passion that made skiing special.

I am both flattered and privileged to have been the benefactor of Joan Rostad’s considerable passion and purpose. Although the concepts presented below are mine, the format and editing are due to Joan’s talent and efforts for which she deserves full credit.

Thank you Joan Rostad for all you done for skiing. This is for you.

Note to the Reader: Since this article was written, my thinking on some issues has evolved and matured. This is what should ideally happen if one is truly committed to the truth.

### Skiing Biomechanics Explained By David Macphail

By: nolo and stins – Posted 9/21/09 • Last updated 4/26/11

1. Introduction
2. Part I. The Secret of Effortless Skiing
3. Part II. Four Key Biomechanical Principles
4. Post Script

### Introduction

David MacPhail was the innovative engineer who created the “MacPod” prototype boot in partnership with “Crazy Canuck” Canadian downhill champion Steve Podborski as an ergonomic advancement in ski boot technology. The MacPod “birdcage” design, which was applauded by scientists in the human performance community, was met with utter indifference by boot manufacturers who never gave it any serious consideration.

The following remarks were selected and compiled from David MacPhail’s writings to the Ski Balance forum that spun off from EpicSki in 2002. At its height of activity, the group consisted of David and me (nolo), Rick Schnellmann (Fastman), Ric Blevins (RicB), Hans Kosak (Biowolf), Lou Rosenfeld (lou rosenfeld), Martin Olson (Martino), and Steve Hultquist (ssh). The forum was active from late 2002 until the spring of 2005, when David’s creative energies turned to golf and the discussion lost its center of gravity.

### Part I. The Secret of Effortless Skiing

If you understand the following principles and rules you will understand the secret of effortless skiing. More importantly, you will be able to teach it to others, and someday there may be enough people with this understanding to influence the ski industry to produce equipment designed primarily for good biomechanics instead of good looks.

### 1. Basic physics

Newton’s Law says, “A body in motion in one direction will tend to stay in motion in that direction unless acted upon by an outside force.” In skiing, gravity is always trying to pull us down to the center of the earth. The low friction base of the skis sliding on snow facilitates a shear force component of gravity that acts parallel to the fall line. You acquire inertia due to the acceleration. The turn effort creates centrifugal force, which wants to eject the skier off the tangent of the arc. The only thing stopping the forces from pulling you downhill is the internal force expressed in the outside leg against a ground reaction force (GRF), assuming balance exists.

### 2. Balance

By my definition, balance is equal and opposite vertical forces aligned in opposition along the same force path with one net external force and one net internal force.

### 3. Skiers are naturally two-footed

Skiing involves more than just standing in place. We are moving from one limb (outside leg) to another. This basic form of locomotion is one of alternating single limb support, the same as walking. It wasn’t until I connected the movements of walking to those of skiing that I was able to perform and coordinate the movements with ease.

When we walk and when we ski we have a stance foot and a swing foot. When you lift your foot to take a step the movement comes from the inertia of the movement of your center of gravity (CoG), but support from the new stance foot makes the movement possible. If you look at a skier in the middle of a turn the inside leg exaggerates the characteristics of the swing leg in walking. When walking, as you swing the unloaded leg forward, this foot naturally inverts. This is the same movement of release of the old stance foot in skiing. Even when constrained by the ski boot the foot will always try to invert when unloaded.

Similarly, as you shift weight to your new stance foot in walking, so do you shift the weight in skiing: the weight first goes to the outside of the foot, and additional weight tips the foot to the inside, which helps to engage the inside edge of the outside ski. The foot’s anatomy is such that it must adapt to the transverse aspect first before it can fully accept the weight of the body. The lateral arch must make contact first and cause the foot to roll into pronation (i.e., evert) in order to tension the arches in the correct sequence.

In the last third (bottom) of the turn, CoG is behind the uphill or swing foot. So the initial active weighting will be on the heel. If the skier initiates movement down the hill by relaxing the support or stance leg while starting to extend on the swing leg, the force will start to drive the foot into eversion. The new stance foot needs to fully adapt to the supporting surface in order to generate a dynamically rigid base of support for CoG. Then the skier has to simultaneously extend both legs to get CoG up and over the ankle of the swing foot in order to unequivocally make it the new stance foot. It is important to note that the extension is gravity-assisted.

### 4. Extension drives pronation

Because (at the end of the turn) the uphill or swing leg is flexed in relation to the support or stance leg, we have an opportunity to extend away from the inertia of CoG–which is being pulled down the hill and down towards the center of the earth. It is important to understand that this is a lateral extension that moves our hips and core towards the center of the next turn, without up motion. We need this extensor effort to create the force in the foot against GRF to drive the outside foot into a pronated, stance position.

This critical moment is sort of a twist on the line of the song New York, New York: “If you don’t make it here you won’t make it anywhere.” If you don’t drive the force in your foot to the ball of the big toe, it will be on the wrong side of the inside edge of the ski at its waist. This will create a situation where you will be using the boot cuff to indirectly transfer power to the ski, and doing so will cause a disruption to the balance system feedback and interfere with effectively skiing from the bottom of the foot.

If you do not drive the force in your foot to the ball of the big toe, as soon as the external forces begin to build, the pronated position of your foot will reverse into supination and your foot will revert back to the adaptive state. Please be clear on this because the end result justifies the effort of extension. Try and visualize what is happening during extension of the swing leg. Your body is pivoting about the uphill or lateral aspect of the foot as CoG moves downhill and over the ski. You have to press with enough force to cause the foot to rotate faster. Additionally, elevating the inside hip greatly assists both rotation around the foot and loading the foot. In this scenario, both internal and external mechanics are pulling the stance foot into eversion and holding the edge. The whole lower limb is turning into the hill.

### 5. External forces can reinforce stability

By simply positioning CoG over the line of force where the ball of the foot is acting within the sidecut of the ski (think of it as literally a line extending from the point the flare of the ski starts to the point where it stops), the forces acting on the skier will reinforce the stability of the base of support even as the forces grow in magnitude. In other words, external forces that would normally disrupt the skier’s balance will have the complete opposite effect in this configuration.

If the skier is using the inner (uphill side) of the boot cuff to hold the ski on edge then the action of the skier is opposing a force that is trying to rotate the stance foot into inversion away from the slope of the hill, which compromises her hold on the edge.

If you get bumped around, you can absorb and fill the surface gaps by letting the ground push toward you on convex surfaces and letting your leg push toward the ground on concave surfaces. The body will do this reflexively if the forces are balanced and the soleus muscle is in eccentric contraction. You don’t even have to think about it. The only thing you have to do is keep CoG in the right place. (This assumes your equipment will actually allow you to do this.)

### Part II. Four Key Biomechanical Principles

1. The pelvis always rotates about the ankle of the stance foot

In the first photo Norm Kreutz is rotating his pelvis towards the outside of the turn about the ankle of his stance foot. This is driving the inside or swing leg in the opposite direction, i.e., into the hill.

In the second photo Norm is relaxing the stance leg and extending the swing leg. This transfers the support of CoG to that leg making it the new stance leg. This action transfers the point that the pelvis is rotating about to the ankle of the (new) stance foot. As Norm extends his legs the pelvis will draw his feet in the opposite direction that it was moving in the first photo. It is kind of like a power assisted rotary move. For this reason Norm does not want to plant his pole until after the extension has begun. This helps stabilize the position of his CoG to ensure rotation occurs in his femurs.

The interesting thing is that this all happens on its own as part of the kinetic flow which should also flow in the direction that starts when the stance leg changes. Once you get the movement pattern right there is nothing to think about aside from deciding when to start a new turn.

2. Kinetic Flow
If there is one area where there seems to be general agreement it is that edging and pivoting occur as a unit movement pattern and not as a series of separate events spliced together. This is why the timing and sequence of the initial move to start a turn is important.

Every turn has a start/end movement sequence that is consistently towards the inside of the turn just as there is a consistent flow in walking. Kick starting the flow is always contrived. This is why the first turn is the most difficult.

The movement that sets up the direction of the flow starts in the feet. At the completion of a turn the flow is to the inside of the turn. To turn in the opposite direction requires that the kinetic flow of the joints of the body be reversed. The outside foot will be in pronation and the inside foot will tend to pronate. In other words the inside foot is already primed to flow to the inside of the new turn.

When Maier relaxes his outside foot (first photo of the turn) his pelvis starts to unwind. This lets CoG drift behind his inside foot. Now CoG is behind his new stance foot and the foot is supported on its lateral or outer border. It is in the same position as it is at heel strike in the adaptive phase of walking.

If you look at the movement of his upper body as he comes out of the fall line you will note that it seems to be coming at you (like a 3D movie) as opposed to going across the hill. If you were standing opposite the gate looking across the hill this would be more readily seen. As his CoG begins to move downhill Maier extends on his (new) outside foot. The foot is initially on its outer aspect but is tending to pronate. Applying force to the foot in combination with the movement of CoG starts the movement of the foot and leg in the direction of pronation. As CoG crosses over his skis his body will become erect with the slope of the hill. In effect, he is ‘standing up’.

Remember, his inside femur was previously moving in a direction in relation to its position with the pelvis that was consistent with supination of the foot (i.e. as the swing leg in walking). The movement of the femur is in opposition to the joint movement of the foot (supination vs. pronation). Maier has to change the relationship of the pelvis to match the flow of the feet.

3. The pelvis always rotates into the stance foot whether in walking or skiing
As he extends on the new inside foot the tension of the rotator muscles in the pelvis unwinds the legs and aligns them with the pelvis, turning the legs into the fall line. As the turning progresses Maier applies rotational effort simultaneously to both legs to pivot the legs across the pelvis so that the inside hip leads the outside hip. In effect Maier creates the natural flow of the pelvis that takes place when one steps R foot – L foot, etc. At the same time he uses the extension movement to bring CoG up and ahead of the ankle of his new outside foot. By this movement Maier synchronizes the flow of the legs to match the kinetic flow of the joints of the outside foot (foot everted, leg turning into the turn, pelvis turned into the outside leg or towards the outside of the turn). Once he has synchronized the flow he exaggerates the rotation of the pelvis to reinforce the pronation of the outside foot as he relaxes onto the outside foot and stretches the muscles in eccentric contraction.

4. The flow of the feet is reinforced by the pelvis
Unless one has a reasonable knowledge of biomechanics the effect of the rotation of the pelvis on edging usually makes no sense because it seems to have nothing to do with the mechanics of the feet. The effect of this movement is that it shortens the muscles that drive the foot into pronation. This not only applies edging force to the ski, it also torques (twists) the ski about its long axis. This is why Maier’s ski bites positively at the shovel. If you compare him to lesser skiers you will typically see skiffs of snow being thrown up off the edges instead of flowing along the ski. This is caused by the percussion of the ski as it oscillates about its edge (into the hill – away from the hill). This is due to insufficient loading of the shovel.
Post Script

Although it is common to speak of kinetic flow starting in the feet, science has proven that the movement really originates out of the pelvic floor, hips, and the abdomen. These muscles will fire first in a functionally fit individual. They do this because they are required not only for stability but also to initiate the pelvic rotation. I think this is why lifting and tilting the pelvis as an exercise is so effective. – Ric Blevins

Compiled and edited by Joan Rostad, September 2006

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