Pilots with above knee amputations will use actuated prosthetic devices and compete along an obstacle course containing ramps, stairs, doors, soft-cushioned seats, barriers etc. Most of the commercially available leg prosthesis technologies are passive ballistic devices, which are easy to control but make uphill walking and stair ascent challenging. In persons with intact legs, especially the knee joint requires much higher capability of joint power generation during ascent than during level walking [3]. Consequently, users of passive prostheses, including microprocessor-controlled dissipative knee prostheses, have to use hand rails and/or perform an asymmetric non-physiological gait to compensate for the missing power generation in the knee (see for example [4] among many other studies). Powered leg prostheses can induce the missing power and in this way solve these deficiencies; however, the control of such devices is not trivial when interfacing them with the user’s motion intention [5]. Additionally, state-of-the-art batteries are either too heavy or lack sufficient capacity to provide power throughout an entire day. The teams at the Cybathlon will showcase new technologies that might overcome current deficiencies.
At the Cybathlon, pilots with amputations of the lower arm or above will use actuated prosthetic hands and arms to complete various household and food preparation tasks (Fig. 2). The dexterity and versatility of currently available prosthetic hand devices is usually limited with respect to the number of grasps and tasks that can be successfully performed. Therefore, persons with unilateral amputations use their intact arm to perform most daily tasks. Bimanual tasks, which require a high load transfer (e.g., carrying a heavy box) or particular fine motor skills (e.g., opening a small jar of jam) are challenging, because they cannot be solved with most state-of-the-art upper arm prostheses. Consequently, up to 60 % of people with upper-limb amputation fitted for conventional upper-limb prosthetic device fail to use it regularly or reject it altogether [6, 7]. The high rejection rate of upper limb prostheses has been attributed to poor training, late fitting, limited usefulness especially for the users with more proximal amputations, and various other factors. Significantly lower rates of rejection can be seen for more advanced, i.e. body-powered (26 %) and electric (23 %) devices [8].
Four out of the six disciplines of the Cybathlon address people with limb paralysis of varying degrees after lesions such as spinal cord injury: Pilots with complete paraplegia will compete in a bike race, where FES devices assist them in performing pedaling movements. FES technology has been used for movement restoration for decades, but has not achieved satisfactory performance due to limitations in setup-time, movement controllability, muscle force magnitude, muscle selectivity and fatigue resistance [9, 10]. Most promising stimulation systems are implanted, as they yield better selectivity and higher force output than non-invasive systems [9, 11]. However, there are drawbacks with respect to invasiveness, risk of infections and costs. Because of these deficiencies, current FES technology has not been accepted by physicians and patients for daily clinical routine [12].
In both the powered wheelchair race and the powered exoskeleton race, pilots with paralysis will master obstacle courses with ramps, stairs, bends, doors and uneven terrain (Fig. 1). More and more companies offer advanced and powerful solutions for wheelchairs. However, control technology does not provide adequate mobility and comfort for many electrically powered wheelchair users, especially under adverse driving conditions [13]. Wheelchair accessibility in public buildings is still limited despite the enforcement of existing laws and regulations [14]. Most outdoor devices are too bulky and not agile enough for indoor use, whereas commercial indoor wheelchairs are not capable of overcoming uneven terrain or steps. So called intelligent or smart wheelchairs have been available for decades, but have not yet been adopted by a large portion of the population [15, 16]. An alternative to wheelchairs are exoskeletal devices that assist people with paraplegic lesions during gait in the upright position [17, 18]. However, battery power is limited to a few hours of operation and the devices are still very bulky and heavy. Most of the commercially available multi-joint exoskeletons have weights in the range of 21–28 kg, with the device “REX” reaching a weight of almost 40 kg [17, 19]. Furthermore, current commercial systems have a limited number of degrees of freedom and reduced ranges of movements preventing the devices from gait on inclined surfaces or stairs. Thus, exoskeletal devices are not yet a realistic alternative for lightweight, energy efficient, and often foldable manual wheelchairs.
In the BCI race, pilots with paralysis of all four limbs will control a virtual avatar in a racing game displayed on a computer screen. The best pilots will be able to distinguish three different commands to overcome three different kinds of virtual obstacles and, thus, will be rewarded by a temporal advantage in the game. A wrong command or a command with too long latency will be penalized by decelerating the avatar on its track. BCI technology is becoming more and more popular, however most systems only function accurately in a lab environment [20]. The time needed for device setup, comfort, cosmetic aspects, function and reliability are still not satisfactory and have prevented broad use and acceptance outside labs [21].
