Mono Ski Terminology

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
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.

Gallery

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