History and hand-cycle technology

Already in 1655, Stephen Farfler ( http://de.wikipedia.org/wiki/Stephan_Farfler ), a watchmaker with paraplegia, built his own, mainly wooden, self-propelled three-wheeled arm-crank wheelchair. In the 1900s and particularly halfway into the twentieth century, solid, yet large and heavy asynchronous hand bikes without gears were used in Europe as transportation modes for persons with disabilities. In the late 1980s, the first modern hand bikes for persons with lower-limb disabilities were developed for recreation and sports. The development of lightweight ergonomic and efficient hand cycles was motivated by the increasing popularity of using the hand bike in a sports setting. Over the last decade, hand-biking in sports gained even more popularity, and was added as an event to the World Championships for the first time in 1998. In 2004, hand-biking appeared for the first time at the Paralympics in Athens ( www.paralympics.org ). Nowadays, Paralympics are closely associated with the “regular” Olympics and receive the accompanying media attention. It is thus expected that hand-biking and other Paralympic sports will increase even more in popularity in the coming years.

A strong ergonomics approach and thus the use of modern technology and lightweight and innovative materials has led to the reintroduction of the synchronous hand cycle in the mid-1980s for outdoor recreational use, where earlier types used asynchronous propulsion. These early hand cycles not only followed rules of bicycle technology, but also mimicked the existing arm-crank systems that became common for upper-body exercise testing in exercise physiology and rehabilitation and showed the first physiologic benefits (higher efficiency and peak power output and lower submaximal physical strain) of full cyclic upper body exercise of asynchronous arm cranking as opposed to hand-rim propulsion.

Disadvantages of the early hand cycles, such as weight, size, and limited maneuverability, have partly been overcome. The use of tracker or attach-unit systems ( Fig. 1 A), an add-on front-wheel crank unit fitted onto a conventional daily hand-rim wheelchair, has made the crank-propulsion mechanism more practical for mobility in daily outdoor life.

Different types of hand bikes. ( A ) A tracker system where an attach-unit with multiple gears and brakes is fixed to the common hand-rim wheelchair. ( B ) A Paralympic racing hand bike with the athlete in a kneeling position.

With the use of the “fifth wheel”, the hand-rim wheelchair can be converted into a multigear-based hand cycle for daily use ( www.doubleperformance.nl ). Here, persons sit in a supine position, comparable to a hand-rim wheelchair seating position. As was shown in different experiments, these hand cycles must be preferred in outdoor wheeling for longer distances over the hand-rim wheelchair. According to DoublePerformance, a hand-bike expertise center in the Netherlands and Belgium, hand bikes can be classified as shown in Fig. 2 . All existing types of (three-wheeled) hand bikes are shown, classified according to whether they are powered by arms alone or by both arms and the trunk. Also, values for frontal area are given, which are important for aerodynamics as is described below. Two-wheeled hand cycles also exist today, but have not been subject of experimental studies so far.

Classification of hand bikes according to whether they are powered by the arms alone or by the arms and trunk. Classification developed by Double Performance, a hand-bike expertise center in the Netherlands and Belgium. ( Data from Double Performance BV, Gouda, The Netherlands; with permission.)

Hand-bike configuration

In sports, frames with a low center of gravity have been developed to optimize aerodynamics in performance. In Paralympics, hand cycles are rigid-frame, three-wheeled (two rear and one front wheel) and propelled by the arms using pedals and a gearing system in front of the athlete (see Fig. 1 B). Different hand-cycle configurations with different sitting postures are used (see Fig. 2 ), including those in which subjects lie completely supine (with low air friction, but with limited use of upper-body muscles), as well as those where subjects are in a kneeling position and actively involve the trunk function in propulsion (obviously at the cost of a higher air friction) (see Fig. 2 ). Those are all tricycle systems. A two-wheeled racer is also available ( www.doubleperformance.nl ). In the year 2000, the kneeling position was first introduced in hand-cycle competition by Kees van Breukelen ( www.doubleperformance.nl ) and today competitors are classified in arm power–only or arm-trunk power competition, depending on sitting position. Athletes compete in three functional divisions, men and women separated: lower-limb function partly or completely impaired and (1) complete loss of trunk stability, (2) a limited loss of trunk stability, or (3) a minimal loss of trunk stability ( www.paralympics.org ).

From an ergonomics perspective, wheeling and hand-cycle performance depends on vehicle mechanics, the hand-cycle–user interface, and the work capacity of the user/athlete ( Fig. 3 ). Each of these components has different characteristics that affect performance in sports and daily life. Such a systematic ergonomics evaluation and subsequent optimization affect performance, freedom of mobility, and endurance.

Flowchart summarizing the ergonomics of the “hand-cycle–user combination,” (ie, factors affecting performance and the subsequent constituents of performance). ( Adapted from van der Woude LH, de Groot G, Hollander AP, et al. Wheelchair ergonomics and physiologic testing of prototypes. Ergonomics 1986;29(12):1561–73.)

In daily life, where rolling resistance and internal friction are dominant resisting forces, maintenance and vehicle mechanics (mass, mass distribution, wheel/tire characteristics, and alignment) are critical. The flowchart (see Fig. 3 ) illustrates elegantly this complexity of performance-influencing factors within a combined physiologic and biomechanical framework of hand-cycling performance.

As stated above, in wheeled sports, different hand-cycle designs are used; important performance criteria include speed and time, but also performance capacity and ability level. With increasing velocity, good aerodynamics is increasingly important given the high velocities and their direct nonlinear effect on power requirement. Minimization of frontal area therefore is critical. In such Olympic sports as cycling and speed skating, minimizing frontal plane area and thus lowering frictional losses are equally important. Yet, aerodynamic design will affect the functional use of upper-body muscles.

In addition to aerodynamics and associated upper-body functions, other factors need to be considered when building a hand cycle for a specific user to improve comfort and mechanical efficiency. Zipfel and colleagues mention crank alignment, seat angle and position relative to cranks, crank handle type, footrest alignment, wheel camber, wheel-base length, gear ratios, seat-to-floor height, materials, and components. Zipfel and colleagues also mention current design problems of commercially available hand cycles: limited adjustability, poor trailing, poor aerodynamics, cables that get in the way of pedaling, minimal shock absorption, noncompatible components, gearing problems (which make it difficult to pedal uphill), difficulty with transfers, heaviness and bulkiness with transportation, and finally footrests dragging on the ground when making sharp turns. Developers have addressed most of these problems with a second-generation hand bike. In developing a third-generation hand bike, more advanced materials, finite element analysis software, and continued incorporation of bicycle technology and overall design innovation are necessary. Further advancements clearly also require continued biomechanical and physiologic study to obtain evidence-based design guidelines.

Hand-bike configuration

In sports, frames with a low center of gravity have been developed to optimize aerodynamics in performance. In Paralympics, hand cycles are rigid-frame, three-wheeled (two rear and one front wheel) and propelled by the arms using pedals and a gearing system in front of the athlete (see Fig. 1 B). Different hand-cycle configurations with different sitting postures are used (see Fig. 2 ), including those in which subjects lie completely supine (with low air friction, but with limited use of upper-body muscles), as well as those where subjects are in a kneeling position and actively involve the trunk function in propulsion (obviously at the cost of a higher air friction) (see Fig. 2 ). Those are all tricycle systems. A two-wheeled racer is also available ( www.doubleperformance.nl ). In the year 2000, the kneeling position was first introduced in hand-cycle competition by Kees van Breukelen ( www.doubleperformance.nl ) and today competitors are classified in arm power–only or arm-trunk power competition, depending on sitting position. Athletes compete in three functional divisions, men and women separated: lower-limb function partly or completely impaired and (1) complete loss of trunk stability, (2) a limited loss of trunk stability, or (3) a minimal loss of trunk stability ( www.paralympics.org ).

From an ergonomics perspective, wheeling and hand-cycle performance depends on vehicle mechanics, the hand-cycle–user interface, and the work capacity of the user/athlete ( Fig. 3 ). Each of these components has different characteristics that affect performance in sports and daily life. Such a systematic ergonomics evaluation and subsequent optimization affect performance, freedom of mobility, and endurance.

Flowchart summarizing the ergonomics of the “hand-cycle–user combination,” (ie, factors affecting performance and the subsequent constituents of performance). ( Adapted from van der Woude LH, de Groot G, Hollander AP, et al. Wheelchair ergonomics and physiologic testing of prototypes. Ergonomics 1986;29(12):1561–73.)

In daily life, where rolling resistance and internal friction are dominant resisting forces, maintenance and vehicle mechanics (mass, mass distribution, wheel/tire characteristics, and alignment) are critical. The flowchart (see Fig. 3 ) illustrates elegantly this complexity of performance-influencing factors within a combined physiologic and biomechanical framework of hand-cycling performance.

As stated above, in wheeled sports, different hand-cycle designs are used; important performance criteria include speed and time, but also performance capacity and ability level. With increasing velocity, good aerodynamics is increasingly important given the high velocities and their direct nonlinear effect on power requirement. Minimization of frontal area therefore is critical. In such Olympic sports as cycling and speed skating, minimizing frontal plane area and thus lowering frictional losses are equally important. Yet, aerodynamic design will affect the functional use of upper-body muscles.

In addition to aerodynamics and associated upper-body functions, other factors need to be considered when building a hand cycle for a specific user to improve comfort and mechanical efficiency. Zipfel and colleagues mention crank alignment, seat angle and position relative to cranks, crank handle type, footrest alignment, wheel camber, wheel-base length, gear ratios, seat-to-floor height, materials, and components. Zipfel and colleagues also mention current design problems of commercially available hand cycles: limited adjustability, poor trailing, poor aerodynamics, cables that get in the way of pedaling, minimal shock absorption, noncompatible components, gearing problems (which make it difficult to pedal uphill), difficulty with transfers, heaviness and bulkiness with transportation, and finally footrests dragging on the ground when making sharp turns. Developers have addressed most of these problems with a second-generation hand bike. In developing a third-generation hand bike, more advanced materials, finite element analysis software, and continued incorporation of bicycle technology and overall design innovation are necessary. Further advancements clearly also require continued biomechanical and physiologic study to obtain evidence-based design guidelines.

Synchronous versus asynchronous

One of the issues that has received some research attention in hand-cycling is the propulsion mode. In contrast to hand cycles in the middle of the twentieth century, which were mainly based on mere bicycle technology, today’s hand cycles all use a synchronous arm mode (ie, both hands propel in phase). This has considerable physiologic benefits (higher efficiency, peak power, lower local strain) as was demonstrated in different studies. Both arms move in the same angular pattern, thus preventing a conflict with the simultaneous steering task, which is expressed in a higher-efficiency and peak-power output. With an apparent constant external workload at the same speed and slope on a motor-driven treadmill for synchronous and asynchronous propulsion, synchronous hand-cycling appears more efficient, with less strain (lower arms/hands) and higher peak performance capacity (speed, power). Some have suggested that the lower peak performance and mechanical efficiency in asynchronous cycling can be explained by increased cocontraction of the muscles in the upper extremities and trunk to combine power production with stable steering. Indirectly, this explains the absence of systematic and consistent differences between synchronous and asynchronous arm-crank exercise, where no steering is required. With a synchronous crank setup, “trunk power,” a new type of propulsion, can be used, as described by, among others, Zipfel and colleagues. However, he use of trunk power is possible by athletes or users with functional trunk muscles and with good abdominal strength. Crank arms can be longer, wider, and positioned further from the body. By leaning forward with each push, the mass of the upper body is used to add power to the stroke. Thus, not only arm, chest, and upper-back muscles are used, but also the abdominal muscles and the lower back contribute to propulsion.