Wheelchair Sports Technology and Biomechanics

Fig. 2.1
The basic components of sports wheelchairs are the wheels, casters, footrests, backrest, and seat

In order to meet the needs of a variety of different wheelchair sports, wheelchairs are designed for each particular sport and most commonly custom fitted for each athlete. Sports wheelchairs are much like sports prosthetic limbs; if they do not become one with the athlete’s body, then performance is negatively affected. Sports wheelchairs are made from a variety of materials; the basic frame components can be made from high-strength steel (e.g., chromium-molybdenum alloy), aluminum, titanium, and composite materials (e.g., carbon fiber, Kevlar, fiberglass). Sports wheelchairs often use different materials for different components in order to meet the needs of the sport and the user. For example, on a basketball wheelchair, the wheel rims and handrims may be aluminum, the spokes Kevlar, the frame titanium, the bolts and axles steel, and the backrest carbon fiber.

Brief History of Wheelchair Sports Technology

The exact history of wheelchairs sports is not precisely known. Likely soon after wheelchairs were invented, people using wheelchairs participated alongside friends and family when participating in sports that could be attempted or modified while sitting. There are accounts of service members recovering from wounds during the First World War participating in sports and recreation activities in their wheelchairs as a part of their therapy or for recreation [1]. Sir Ludwig Guttmann is credited with establishing organized wheelchair sports, which eventually led to the Paralympic Games as we know them today [2]. World War II led to tremendous numbers of both civilian and military casualties, as well as remarkable advances in medical treatment and eventually rehabilitation. This as in other wars led to people living with new and more severe disabilities than had been the case heretofore. For example, advances in treatment of post-traumatic shock and the creation of penicillin led to people living with spinal cord injuries for years and eventually decades. The large numbers of mostly young people, many of whom were veterans, living with disabilities had a twofold effect: (1) first, there were a critical mass of people with previously unknown chronic disabilities and (2) they wished to be active and whenever possible leave hospital settings and live in their home communities [3]. This led to two largely parallel movements, at least early on: the creation of multi-sports events such as the Paralympics today and wheelchair basketball—later to become a Paralympic sport. For nearly four decades from the 1940s through the 1970s, athletes competed in nearly the same wheelchair for every sport with minor modifications [4]. During this time frame, people modified their daily-use wheelchairs to improve their sports performance. For basketball, the common modifications were to remove the armrests (sometimes cutting them off), remove the parking brakes, and lower the backrest in order to provide greater freedom of movement for their torso. For wheelchair racing, athletes made many of the same modifications, but in addition they would lower the seat and move the rear axles forward to access a large portion of the handrims to go faster.

In the early 1980s wheelchair sports began to make a tremendous transformation to enter into the modern era as it is now recognized [5]. Athletes began to challenge traditional thinking and the rules of wheelchair sports established primarily by clinicians, rehabilitation administrators, parents, and other well-meaning people. As a part of the worldwide disability rights movement, athletes also wished to take control of their sports, make changes in their equipment, and increase opportunities for competition—some with the goal of achieving parity with able-bodied sports. The biggest impact was that wheelchairs for particular sports began to become available, especially for basketball and racing. To provide some context, at the beginning of the decade, the world record for the mile (1609 m) was a fraction under 5 min, and by the end of the decade, the record had dropped to under 4 min; and by the 1996 Paralympic Games, all of the finalists in the 1500 m were capable of finishing the mile in less than 4 min.

Importance of Seating for Sports Wheelchairs

The seating system is an important interface between the wheelchair and its user and has a direct influence on an athlete’s performance and ability to control the equipment and therefore should include the following basic three goals: (1) fit snug and comfortable like a good shoe, in order to promote a firm and stable base of support for propulsion and control; (2) provide a stable support to maximize the balance of the user for the sport activity; and (3) reduce the risk of developing pressure sores, skin breakdown, bruising, and other soft tissue injuries [6].

The overall fit of the seating system can easily be checked by asking the user to do a “twist,” and the chair should move with the user. The chair will also respond to the user shift in center of gravity (COG) and will “stay” with the user during quick turns and lateral movements especially when operating in tight, narrow, and semi uneven environments [7]. If the width of the seat is too wide, it will result in a loose “sluggish” fit, with the user “twisting” within the seat, which may lead to skin break; or if the shoe is too big, it causes “blisters. The length of seat depth should be selected so that there is at least 2–3 in. space between the front edge of the seat and the popliteal area behind the knees. If the seat is too long, the tendency is to slide forward causing the pelvis to rotate posteriorly which increases the risk of developing a sacral sore and back pain. A snug and well-fitted seat allows the shoulder joints to be in a neutral safe position that will enhance the biomechanical efficiency of the upper extremities, therefore reducing the risk of repetition strain injuries.

The orientation of the seat in combination with the back rest support has to be designed and adjusted to provide a stable support to maximize the balance of the user for the sport activity. The hand position in relationship to the elbow angle will show how “low” and/or how “high” the user is sitting in the chair. With the upper arm along the trunk and the hand at top dead center on the push rim, the elbow angle should be 90–120° for efficient self-propulsion. A “low” vertical position (elbow angles ≤ 90°) or a “high” vertical position (elbow angles of ≥120°) with the user sitting “on top” of the wheels can be corrected by selecting an appropriate height cushion, adjusting the seat dump, and selecting an appropriate wheel diameter [8]. Selection of rear wheel size can provide a wider range of positions, as wheel diameters of 22–26 in. are commonly available. The seat dump is the angle of the seat with respect to horizontal. About 5° of posterior tilt is common; yet a larger seat dump helps to increase pelvic stability by holding the pelvis against the backrest, helps to compensate for decrease trunk stability, and reduces the angle between the thighs and the trunk which helps to improve balance; straps may be used to further hold the user firmly in place. Yet caution should be applied as a larger seat dump may promote pressure sores on the back and affect the COG distribution as it may decrease the rearward stability and increase tipping of the chair; transferring out of the wheelchair will be more difficult. The backrest height should be set as low as possible to provide support to the lower back and allow the upper torso to move freely, however not too high to inhibit movement and biomechanical efficiency of the upper extremities.

The risk of developing pressure sores, skin breakdown, bruising, and other soft tissue injuries for wheelchair sports can be minimized if the athlete recognizes that the same preventative strategies that keep him/her healthy outside the sport with the use of their everyday equipment are the same strategies that will keep him/her healthy with the use of specialized sport equipment [9]. These preventative strategies include recognizing risk, decreasing the effects of pressure, assessing nutritional status, and preserving the integrity of the skin by reducing pressure, friction, and shear forces. Pressure sores commonly occur with prolonged sitting on a bony prominence and hard surface, and the risk can be reduced by increasing the surface area of the seat in contact with the body and providing firm padding that will closely fit the contour of the athlete’s body in the seated position for the sport. A snug and well-fitted seat will reduce the friction and shear forces, and straps can further hold the athlete firmly in place. In some cases, the seat is molded to the user to form a custom seating orthotic. Other biomechanical causes of skin breakdown athletes with paraplegia need to keep in mind include pressure from tight clothing or shoes and trauma to insensate lower extremity during transfers.

Of note: it is important to conduct frequent inspections of the equipment and conduct regular maintenance and timely replacement of any worn-out/damaged seat components to reduce the risk of lacerations and injuries.

Wheelchair Slalom

The slalom is an obstacle course race designed for wheelchair users. What began as a simple obstacle course at VA hospitals to help veterans practice on uneven terrain has grown to a competition at the National Veterans Wheelchair Games that is one of the most popular events for athletes, therapists, families, and spectators. This event creates obstacles (only limited by the imagination of the course design team) to simulate everyday mobility challenges a wheelchair user may encounter, such as turns, changes in direction, ramps, curbs, steps, uneven terrain created with robes, planks, ladders, soft terrains such as gravel and sand pits, as well as doors, narrow passage ways, even small tunnels, and so on. The slalom course demands of the athlete speed, coordination, strength, and technique in negotiating the obstacles in the least possible time making as few mistakes as possible.

The design of the course and its difficulty vary depending on athlete’s injury classification and type of wheelchair used. For example, for powered wheelchair users, the design of the course will challenge the athletes in precision driving by requiring highly skilled operation of the joystick, head control, chin joystick, sip-and-puff, etc. while skillfully maneuvering the power base through turns, changes in direction marked by cones, over small ramps, and through semi uneven terrain at fast speed with very few mistakes. All athletes are required to wear a helmet and will use their everyday power wheelchairs for competition. Official score keepers are present on the course, and official “spotters” provide for the safety of the athlete.

For manual wheelchair users, the design of the course varies depending on athlete’s injury classification and competition category. All athletes are required to wear helmets and most of them will use their own manual wheelchair. No specific type of manual wheelchair is required; however, athletes competing in ultralight manual wheelchairs, which fit “snug” and with legs and feet strapped securely to the chair, have a better chance to do well in the slalom course. The profile and inflation pressure of the wheelchair tire will have an effect on how well a tire can “grip” an obstacle, for example, knobby tires that are slightly underinflated will provide a nice grip to climb over an uneven obstacle yet will perform slower on flat surfaces during fast turn and change of directions tasks; on the other hand, high-pressure slick tires will be faster on flat surface during turns and change of directions task yet may “slip off” of uneven obstacles. The fine-tuning and selection of “strapping” and “tires” depends on each athlete’s abilities and preferences. During the slalom competition, the official score keepers are present on the course with at least four trained “spotters” to provide hands-on assistance for safety to catch athletes from tipping and/or falling onto/off obstacles.

The Super G, or Super Giant Slalom, is a featured event and scheduled on the last day of the competitions to draw the general public to the NVWG. It is the ultimate course designed for a selected group of highly skilled manual wheelchair users, all top three “finalists” who qualified in their individual categories. The competition is very intense and full of energy as athletes “fly” over the most challenging obstacles, with skilled control, precision technique, strength, and high speed in order to beat their competitors’ times while having fun with the ultimate goal to be the fastest Super G winner [10].

Wheelchair Basketball

Originating in the 1940s, basketball is one of the oldest wheelchair competitions and is currently played in more than 100 countries around the world [11]. Wheelchair basketball is played by two teams of five players on a regulation basketball court with a hoop on either end and standard markings for both free throws and three point lines. The goal is to work the basketball down the court either individually through dribbling or as a team through passing in order to score a greater amount of points than your opponent by making the most baskets.

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Feb 25, 2018 | Posted by in SPORT MEDICINE | Comments Off on Wheelchair Sports Technology and Biomechanics

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