This chapter contains sections titled: Introduction, Cycling mechanics, Muscle mechanics, Neural control, Cycling in challenged pPopulations' conclusions; References. The cycling task is used in a variety of applications including high level competition, exercise conditioning, rehabilitation, and research. While the focus is on performance, each application presents a set of conditions unique to rider position, bike setup, and cadence and load demands. For example, the position of the rider on the bicycle, load, cadence and the set up of the bicycle during competition will be specific to each rider and may even change during any given competition, e.g., long road races. Likewise, during a period of rehabilitation, the position of the rider, the load, and the cadence selected will be specific to the disability, e.g., knee injury versus stroke rehabilitation and the bike will be adjusted to accommodate the rehabilitation plan, i.e., it can change as the training or recovery plan progresses. The common element to all situations is the requirement that the interface between rider and bicycle, including the selecrion of the appropriate load and cadence, maximizes their experience and enables them to achieve the greatest result. Giving appropriate consideration to where muscles might function at their best given their individual mechanical properties, e.g., length-tension and F-V properries, fiber type, and so on, the quality and training state of the muscle, and how the nervous System might best use these properties in control of the cycling task, modifying bicycle components to capitalize on the individual's unique motor capabilities will enhance the rider/bicycle interface and hence maximize performance. There are a variety of bicycle designs used to achieve specific goals during competition, exercise, and rehabilitation. Stationary bicycles are most commonly used in rehabilitation for reasons related, in part, to safety but the bicycle can be upright or recumbent and have a variety of seat, handlebar, and/or pedal designs. Seat tube angle (STA) and mechanisms designed to regulate load can vary substantially as well. Competitive bicycle design may also vary substantially, e.g., road bicycles, mountain bikes, and so on, depending on the demands of the particular competition. Wind resistance is another factor that influences rider position in competitive road and track cycling but is not considered in the clinical or experimental environments. In all of these situations, the bicycle/rider interface will affect muscle function and influence how each muscle and/or group of muscles performs. The purpose of this chapter is to describe how the cycling task has been used to study muscle mechanics and neural control. Being able to "personalize" the interface between the rider and the bicycle allows the trainer, coach, scientist, or clinician the ability to provide, for example, the range of motion necessary to enhance proprioceptive input in patients with certain neuromuscular disorders, to ensure muscle is able to use its mechanical properties to their advantage, to utilize the rhythmic nature of the task to address problems faced by individuals with neurodegenerative disease, or to modify load to challenge muscle strength and per-formance. Emphasis in this chapter will be placed on the muscles in the lower extremity, as they assume the primary role in the production and transmission of power to the bicycle (note: the muscular system is considered a mechanical system as is the bicycle) and, as a consequence, endure the larger loads. A review of cycling mechanics will be followed by a discussion of general muscle mechanics and physiology related to cycling; muscles are major force producers as well as sensors that provide both length and force feedback, for example, to the nervous system during movement. Finally, we will discuss the use of the cycling task in the study of the neural control of movement with an exemplar application to a physically challenged population.
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