It's All Downhill
Reprinted from SNS November 2000During the years I've spent designing and building mono-skis, I've learned to draw on the experience of others. Motocross-suspension experts can work wonders with mono-skis, wheelchair-seating and road-racing specialists can provide insight regarding seating and body-positioning technology, and ski designers and tuners can apply their knowledge to the selection and tuning of appropriate skis.
Every mono-skier needs to be somewhat of an expert in all these fields. If you want to buy your own mono-ski, first take lessons and try out the program equipment. Get as much experience as possible so when you're ready to make a purchase you can choose the equipment right for you.
If your mono-skiing program plans to buy new equipment, do research and ask around to determine which type will provide the greatest flexibility and adjustability for a variety of users. Take the time to carefully set up equipment for your students. Sending them onto the slopes with improper ski positioning leads to frustration and wasted time.
Mono-skiing can be dangerous. Athletes must balance on a single ski while moving at high speeds. The lower body is securely positioned in the equipment. This means that during a fall, the mass of equipment and body can come down on the shoulders, head, or neck, causing severe injury.
New skiers are often eager to move onto faster, steeper terrain before they're ready. Even when this doesn't lead to accidents, they often exceed their balance capabilities and develop habits of leaning into the hill and banking, which will prove detrimental to their long-term skills.
It's important to learn how to fall. I discovered the hard way that trying to stop the fall with my outriggers was a mistake. Now when I fall I tuck my outriggers into my sides and try to slide. Mono-skis tend to stop quickly anyway.
All programs should teach students how to fall, and they should keep incident records on file. Such information is invaluable for improving mono-ski design and training methods.
Mono-skis enable people without the use of both legs to ski. Bi-skis have two skis and a mechanism that angulates (the act of shifting body mass to the side in order to put the ski on edge) them into the snow when users lean on the equipment. Think of the equipment from a technical viewpoint: a dynamic skiing orthosis.
A mono-ski and a customized leg prosthesis with hydraulic dampeners have a lot in common. Both must be custom-fit to the remaining functional body component, and both use cams, artificial linkages, and other components to bridge the gap between the body and the ground and hydraulic components.
Try to find an adaptive ski program with staff members who are experienced and certified as instructors through the Professional Ski Instructors of America (PSIA). PSIA offers Level 1 certification for mono-skiing and bi-skiing, and Level 2 and 3 instructors are able to teach at more advanced levels.
A good instructor will try to determine students' levels of previous experience and other related sports interests. They will also try to learn a little about students' general fitness abilities, learning styles, and their goals and expectations for a particular lesson or group of lessons. A certified instructor can make the entire learning process more rewarding and less frustrating. It's important to share specific information you have about primary or secondary disabilities as well as medications you're taking that might affect your balance or attentiveness on the slopes.
If it's been less than a year since your spinal-cord injury (SCI), the program will probably require a medical release from your doctor. If you?ve had a back fusion, to allow healing don't try skiing until a year has passed.
The assessment for your lesson is based on determining your fore/aft and lateral balance as well as flexibility at the waist, knees, and trunk; this will determine seating in your ski. Arm and grip strength indicate whether you want to bi- or mono-ski. It's possible for people with T5 injuries and above to bi-ski, but the higher your injury level the more challenging and often frustrating it can be learning to balance and control a mono-ski.
If you're an aggressive person and your heart is set on mono-skiing, give it a try. On the other hand, if you don't plan to ski often and just want to have fun, bi-skiing is a way to get started quickly and participate with family and friends.
Mono-skiers must recognize the hazards of a winter environment. They need padding or cushioning to protect their skin from impact and pressure, and they should choose clothing that won't bunch up or cause wrinkles in the seating area. Long underwear and stretch ski pants are good for racing, but they can be inconvenient when you're wearing urinary-drainage hardware. Oversized warm-up pants allow more room, and after-ski boots provide protection and warmth. Avoid boot heaters, as several U.S. Ski Team members have experienced burns from them because they can't feel the heat.
Wear goggles whenever possible, but avoid sunglasses that can break and cause facial injuries. Helmets are required for Super G or downhill, and they are critical for slalom when training with gates that can strike skiers in the face or in the back of the head.
Always wear a helmet when mono-skiing. When you spin around backward, it's quite common for the tail of the ski to dig into the snow and flip you backward onto your head. And since your mono-ski is not designed to release from your ski, if your ski gets caught, a fall can result in tumbling. A helmet's greatest benefit could potentially be during chairlift loading or unloading. If you get hit by another person or the chairlift, your head is protected.
Shoulder exercises are important for building strength and preventing injury. Wheelchair users are good at muscle actions that involve pushing forward, but mono-skiers must resist forces that push the arms up and back. To develop those muscles, perform exercises by raising your arms in various positions while using bungee cords or light weights to help strengthen rotator-cuff muscles.
When setting up your own or program equipment, use the appropriate seat cushion to provide pressure relief. Stabilize your pelvis in a dynamic position so you're not sitting back or slouched in the mono-ski. Position the feet and knees to allow as much forward flexion as possible. Your trunk should be in an upright and active position so you can quickly react moving fore and aft.
If you own your equipment and you're trying to determine what to put underneath your mono-ski, consider the newer shaped skis, but not radically shaped ones. Shaped skis can be a disadvantage for people just learning, but the skis can allow individuals to make nice turns once they develop to the intermediate level.
Setting Up Your Mono-ski
The first step is to get the skier positioned in the mono-ski, with proper foot and knee height and the pelvis tilted forward in an upright position.
Part I: Adjusting the Fore/Aft Positioning of the Skier's Center of Mass Over the Ski
Step 1. Measure the ski from tip to tail across the top, and mark the midpoint of the ski on the side with a marker or piece of tape.
Step 2. Determine the natural upright balance point. Find a triangular block of wood or a large-diameter wooden dowel 6-12 inches long. When placed perpendicular to and beneath the ski, it should lift the ski about two inches off the ground. With the skier in a neutral, upright position, find the balance point and mark it on the side of the adaptive ski frame.
Step 3. Slide the wooden block forward, and with the skier in a full forward skiing posture, determine the forward-most balance point and mark this on the side of the adaptive ski frame.
Step 4. Move the wooden block back, and with the skier in a rearward skiing posture, determine the rear-most balance point and mark this on the side of the adaptive ski frame.
Step 5. For a new skier, the midcord mark on the ski should be midway between the forward-most and rear-most balance point (or it can be closer to the neutral point); adjust the binding as necessary.
If you mark these three points permanently on your mono-ski frame, they can be used as reference points for mounting your ski and making later adjustments in the ski position. When mounting the mono-ski system on the ski, start with the neutral center-of-mass balance point directly over the ski's midcord position or halfway between the forward-most and rear-most balance points.
Adaptive ski-program staff can mark the midcord position on the program's skis and place marks on the frame of the mono-ski at one-inch increments, well forward and aft of the various balance points. Numbering or lettering these marks will allow you to keep track of where the ski should be adjusted for each skier.
When first-time skiers use program equipment, they can get in the ski and find their neutral, forward, and aft balance points. Skiers can remember the mark on the mono-ski frame that corresponds to where the midcord position of the ski should be. In the future, they know to set the position for that particular mono-ski to the same mark they used during their last visit. If a program has many differently-marked mono-ski frames, they should have names or numbers so skiers can remember which ones they used. Manufacturers might be encouraged to provide their equipment already marked for program use as well as for individual skiers.
Part II: Measurement of Left and Right Angulation Ability for Canting
Step 1. With the skier fully strapped into the mono-ski and a full-length ski attached, position the ski on a piece of thick-pile carpet or foam that will allow the skier to rock back and forth and side to side.
Step 2. Position an inclinometer across the ski, as close as possible to the ski's mounting point. Have the skier angulate as far as possible in one direction. The outriggers should barely touch the ground, and the skier should be leaning over to keep from falling over. Measure the maximum angulation angle that can be reached in each direction.
Step 3. If the amount of angulation in each direction is equal, no further adjustments are necessary. If a skier can angulate farther in one direction than the other, the ski can be canted. For example, if the skier can angulate 10 degrees in one direction and 6 degrees in the other, a 2 degree cant will enable him or her to angulate 8 degrees in each direction. Although canting is ideally done on the ski, seat canting at the mounting point works well. In a program ski, insert stiff foam into one side of the seat shell to shift the skier to the side.
Part III: Measurement of Rotational Ability
Not all skiers have the same range of rotational ability. Some can turn their upper bodies more in one direction than another, and this inequality can limit their ability to make equal turns in both directions.
Step 1. Have the skier rotate as far as possible in each direction, noting the angle of trunk rotation at the shoulders.
Step 2. If the amount of rotation in each direction is equal, no further adjustments are necessary. If he or she can rotate farther in one direction, rotate the seat to compensate. For example, if the skier can rotate 20 degrees to the left and 10 degrees to the right, a 5 degree seat rotation will allow him or her to rotate 15 degrees in each direction.
Safety and Accessibility Standards
The American National Standards Institute (ANSI) B-77 Standards Committee is the authority that develops safety and performance standards for aerial tramways and passenger lifts, including chairlifts and gondolas. ANSI has been asked to incorporate accessibility standards, where appropriate, into its current safety and performance standards for lifts.
The accessibility standards include issues related to disclosure. The requirement for disclosure of the chairlift loading height, a maximum unloading height of 21 inches—the requirement for level loading into gondolas and trams—and a variety of other more detailed access issues have been included in the standard?s new version.
The ANSI/RESNA (Rehabilitation Engineering Society of North America) Technical Guidelines Committee has formed a subcommittee on standards for recreational equipment for people with disabilities. The first subgroup in this committee has drafted guidelines for adaptive sit-, mono-, and bi-skis.
Manufacturers and others who want to learn more about these guidelines may contact Peter Axelson, Beneficial Designs, 5858 Empire Grade, Santa Cruz, CA 95060, (831) 429-8447, 423-8450 (fax), firstname.lastname@example.org (e-mail).
A definite need exists for a standard method of measuring chairlift-clearance height so skiers can become familiar with what heights work for them. For this to be effective, chairlifts and equipment should be measured in a standard way.
The ANSI/RESNA Technical Guidelines Committee has formed a subcommittee on adaptive sports equipment to create safety standards for sit-, mono-, and bi-skis. The standard was in a pre-ballot procedure in the Fall 2000, with final balloting expected in 2001. The standard includes requirements for evacuation harnesses and retention lines strength testing.
If manufacturers indicate they comply with a standard, their equipment complies, they are disclosing much of the information discussed in this article in a manner that is consistent, and they disclose this information in their technical product literature.
This subcommittee will meet in conjunction with the Ski Spectacular in Breckenridge, Colo., December 7.
Aluminum. This is a material often used in the fabrication of mono-skis and lightweight wheelchairs (usually 6061-T6). Commonly used in the aircraft industry, aluminum can be painted or anodized but will corrode if left untreated. It is easily machined and tends to get stronger when cold-formed.
Angulation. This is the act of shifting body mass to the side in order to put the ski on edge. To balance this action, an equal portion of body mass must lean in the opposite direction or the ski can lose its edge and slide out from under the skier.
Body Height. Mono-skiers can't effectively shift their center of mass if they're seated too high. The center of mass should be as close to the snow as possible without touching the snow when leaning into the hill on a steep slope.
Bucket Seat. This is the basic seat type that often comes on a mono-ski; it is usually a plastic or fiberglass shell. A simple pad may be provided, but users generally customize their seating and padding. A Jay protector is often used in program equipment for pressure relief. The seat should allow good pelvic positioning and the ability to lock the pelvis to prevent twisting. Individual knee straps are also important for locking the pelvis in position.
Cage Seat. This is the type used on road-racing wheelchairs. The concept hasn't been tried on a mono-ski, but it has potential for adapting to different body sizes.
Canting. Cants are plastic wedges placed between the ski and the ski boot. Mono-skiers with scoliosis (curvature of the spine) or differences in left-/right-side muscle strength may need canting. Users can cant the seat relative to the frame, but it's better to cant between the frame and the ski.
Center of Mass. This is the point at which the mass of the body and mono-ski are concentrated. Positioning the center of mass over the proper spot on the ski is essential to making turns. Mono-skiers have much less ability to shift their center of mass forward and backward than stand-up skiers. To maintain balance when making turns, the center of mass must also be centered properly on the ski to the left and right (see "Fore and Aft Adjustment").
Chairlift Clearance Height. Chairlift height is affected by the amount of snow on the load ramp. Since April 2000, the new aerial tramway standards require that ski areas disclose the seat loading height at the load point for all chairlifts. This is the distance from the load point to the top front edge of the chairlift seat. If you place your mono- or bi-ski in the chairlift loading configuration you can measure this height with a tape measure while you're sitting in your equipment on a firm surface. This chairlift seat-height information is a great safety feature for adaptive skiers because it tells them whether they can load when the lift is running at full or slow speed, or if it needs to be stopped to give them more time or get assistance.
Composites. This is a combination of woven materials (e.g., fiberglass, Kevlar, graphite) infused with liquid resins (e.g., polyester, vinylester, epoxy) that harden. Epoxy resins are less water-permeable and provide great flexibility and durability at all temperatures.
Compression. Stand-up skiers use their knees to compress their bodies as they go over bumps. If they didn't, they'd get a jolt and possibly go airborne. Mono-skiers have to let their shock absorbers do the work. Some have adjustable slow/fast compression rates. For example, rolling over a bump would cause a slow compression rate, while hitting an abrupt one would cause a fast rate.
Dampener. If you remove the spring from a shock absorber, you have a dampener that controls the rate of compression and rebound. A dampener is a piston with hydraulic fluid on both sides. A tiny hole in the piston limits the rate at which it can move through the fluid. A change in the hole and valve size affects the slow/fast rate of compression and rebound. Some dampeners can't be adjusted.
Evacuation Harness. Evacuation equipment provided for stand-up skiers in the event of a chairlift malfunction would most likely be useless to adaptive skiers, so they should carry a personal evacuation device at all times. Adaptive sports-equipment standards were in the pre-balloting process in Fall 2000, and a complete adaptive-equipment standard for evacuation-harnesses testing should be completed in 2001.
Flex. This ski characteristic may be linear or nonlinear, soft or hard. The mounting of the mono-ski to the ski should not interfere with the natural flex. The heel piece on a standard binding is spring-loaded to allow the ski to flex naturally. On the mono-ski, if the distance between mounting bolts cannot change as the ski flexes, the bolts will eventually tear loose. This can cause the ski to break near the mounting plates.
Foot-support Height. When full mono-ski suspension compression occurs, your feet should be as low as possible without hitting the snow. When your feet hit during the driving portion of a turn, you completely lose your edge; therefore, always consider the slope's steepness.
Fore and Aft Adjustment. This is a mono-ski's most important adjustment feature. Able-bodied skiers can shift their center of mass fore and aft over the ski in a much broader range than mono-skiers. As a T10 paraplegic, I have a total range of 12.5 cm (about 5 inches), while a stand-up skier can normally shift 32 cm (12.6 inches). Programs should look for mono-skis with fore/aft adjustments in increments that will accommodate a variety of body shapes and sizes. It is also important to know how easily the adjustment can be made and readjusted on the ski slope.
Inclinometer. Inclinometer. A simple tool used to measure the ski?s angle, the inclinometer is necessary for lateral adjustment of center of mass and measurement of left/right angulation for canting in setting up your mono-ski. You can purchase an inclinometer from Sears (part #9GT3984) for about $15.
Knee-support Height. Knee height determines thigh angle. Set knee height and thigh angle to accommodate your functional balance: The less upper-body stability, the higher the knee height. Adjustment of knee-support height should enhance function, not accommodate the skier's size. A separate strap around the front of each knee should lock the skier's pelvis back into the seat. A single strap around the front of both knees allows the knees and hips to move inside the strap.
Lateral Adjustment. This is the ability to adjust the seat position left and right on the mono-ski frame. Lateral adjustment (not to be confused with canting) can be done at the ski or at the seat and is used to adjust the skier's center of mass laterally over the ski.
Lateral Trunk Stability. People with higher spinal-cord injury (SCI) lesions who cannot control lateral stability will need to adapt the seating system to support their torso without overly limiting movement. Paras (T10 and above) have successfully used rubber inner tubes and fiberglass spring rods to extend the seat back and give them upper-body support. A chest harness made with bungee-cord or inner-tube material can also provide stability, and some harnesses interface with single and double flexible fiberglass rods behind the spine, allowing users to flex forward and to the side, then spring to an upright position.
Lifting Points. Lifting points are usually located near the seat and are used to assist with loading and righting fallen skiers. Mono-skis used for racing do not always have lifting points.
Midcord. The midcord is the middle of the ski. Measure the straight-line distance from the tail to the tip of the ski and divide this distance in half. Then measure that distance from the tail of the ski. This is the midcord. For adjusting the ski position, it's important to know where you want the midcord position of your ski relative to the ski frame. (See "Setting Up Your Mono-ski, Part 1: Adjusting the Fore/Aft Position of the Skier's Center of Mass Over the Ski.")
Mounting Plates. Mounting plates are used to attach the mono-ski to the ski. Many ski manufacturers now use standard bindings to do this. A serious racer will need spares and should find out how long it takes to change the ski.
Orthosis. This device assists body functioning by providing external bracing or support to limit or facilitate proper range of motion (ROM).
Outriggers. The simplest outriggers are forearm crutches with short ski tips attached to the ends; those custom-made are usually lighter. Outrigger cuffs are stainless steel or plastic and can be flexed to make them smaller or larger. If cuffs open on the inside of the arm, they can more easily peel off in a fall. Almost all outriggers have flip locks that allow ski tips to flip up so skiers can use the tail of the ski to push around. Sometimes a steel claw or ice screws are attached to the tail of such skis. Limiting the pivots of the ski tip improves ability to use the tail of the outrigger as a brake; the amount of pivot in the outriggers can be increased as less braking is needed. The outrigger angle should be set so it runs smoothly along the snow. A mono-skier should avoid touching the tail of a rigid ski on snow at high speed. Look for outriggers that have a handgrip mounted at a forward angle. This is the wrist's natural resting position and is more functional and comfortable than a right-angle handgrip.
Pelvis Tilt. People with SCI tend to sit with their pelvises tilted back in low-back, lightweight wheelchairs. While fairly stable, this posture is not dynamic and causes lower-back pain. In a mono-ski, the pelvis must be rotated forward and supported in a more dynamic position.
Pivot Points. A mechanism without shock absorbers moves because it has at least one pair of pivot points. A mono-ski with a four-bar linkage mechanism has eight pairs of pivots. The system lasts longer with bronze or nylite brushings and even longer with bearings.
Quick-release Ski. Many new mono-skis use a standard boot plate and competition bindings to hold the plate to the ski. In this case, small tabs are often placed at the toe of the boot plate to prevent the toe from releasing on the binding.
Seating Orthosis. Most top U.S. mono-skiers use customized seating orthoses. If you decide to have an orthosis made, it is important to be familiar with many different mono-skis so you can determine your most functional body position for skiing. Know where you want your feet, knees, pelvis, and upper body positioned over the ski. Ideally, make a mock-up of the support structure or, better yet, sit in your mono-ski during the plaster splinting process with your orthotist. An orthotist's services are worth trying to get your insurance company to pay for, since it is the most important and probably most expensive piece of adaptive equipment needed to interface you to the sport of skiing. A well-cast mold can also be used to make seats for racing wheelchairs, kayaking, cross-country skiing, etc.
Self-loading Lift Mechanism. This raises the mono-ski from skiing height to chairlift loading height. Find out if additional hardware is required and how long it takes to actuate the mechanism. Determine if assistance is required and how much weight this part of the mechanism adds to the mono-ski.
Shock Absorber. The shock absorber, which comes in a variety of lengths and ranges of travel, consists of the hydraulic dampener and a spring. "Travel" is the distance the shock moves from full extension to full compression. Spring rate and dampening ratios are determined by the height of the bumps and the speed at which you plan to go over them.
Spring. The spring on many shock absorbers is removable. Variable spring rates are available; a softer spring works better on a downhill course, and stiffer ones are better on a slalom course.
Suspension Linkage. The suspension-linkage configuration determines the path of movement the skier's center of mass will take from full compression to full rebound. A scissor-type mechanism and a single-pivot linkage allow only vertical movement. Four-bar linkages may have short or long bars; depending on their angle, the longer will likely result in less forward displacement. For safety reasons, do not use any suspension that only moves part of the body. The shock absorber's position and orientation have nothing to do with the relative path of the mechanism's movement.
T-bar Hardware. If you ever ski in Europe, you'll encounter many T-bar lifts. In choosing hardware to use with a T-bar, consider the best attachment point to the mono-ski. Pull in front of and slightly above the skier's center of mass.
I use hardware that attaches to my knee support: A loop of line goes from my left knee to my right, with a quick release at both knees. At the front of the loop, a plastic-coated rope covers the line and is looped over the T-bar. I keep a release line in my hand while riding up. At the top, I pull the line to open the rope. If that gets frozen, I can release the attachment points to my mono-ski at the knees. This is a triple-redundant system; I recommend at least a double-redundant system. Don't rely on your ability to release a plastic buckle. I saw one team member get wrapped around a post going up the T-bar, and the failure of a plastic buckle is what saved his life! Be sure to have a good release system.
Vertical Displacement. This is the total vertical movement from full compression to full rebound, measured from some point on the mono-ski perpendicular to the surface of the snow.
Weight of Equipment. The lighter the better. Remember, someone has to carry these things. A pair of inline-skate wheels can be attached at the binding to enable your ski to be pulled along the ground.
The November 2000 S'NS includes the previous article as well as a chart comparing 14 sit skis.