Cycle exercise machines, sometimes also known as "stationary bicycles", have been known for some time. These exercise machines typically include a seat much like a bicycle seat, for supporting a person sitting upright on the machine, and a foot-powered crank arrangement mounted below the seat. This crank arrangement in prior-art cycle exercisers includes a pair of crank arms extending outwardly from a rotatable shaft, with foot pedals mounted at the free ends of the crank arms. The crank arrangement is mounted for receiving the feet of a person seated on the exercise machine. A drive chain or belt transfers the rotary motion of the crank arrangement to an energy-absorbing device such as a flywheel or rotor, which provides a load force against which the exerciser expends energy while pedaling the crank mechanism. One such cycle exerciser is disclosed in U.S. Pat. No. 4,188,030 to Hooper.
Because cycle exercisers of the prior art use a crank mechanism which the user pedals while doing work on the machine, these exercise machines cannot provide a constant transfer of power from the user to the load throughout the entire stroke of each pedal. Crank pedal mechanisms have a null at the top and bottom of each stroke, where the effective length of the pedal crank arms diminishes to zero length as the crank mechanism passes through the dead center position. The effective lever arm of the pedals then increases sinusoidally to the maximum effective length as the pedal crank arms pass through the 90.degree. position, i.e., half-way between the top to the bottom of each stroke. Because this effective lever arm constantly changes, the rate at which the exerciser can effectively expend energy doing work on the load device likewise changes throughout each stroke of the pedal. This variation lessens the possible maximum efficiency of cycle exercisers, as the rate of energy transfer for each stroke is maximized only momentarily during each stroke.
Another disadvantage of existing cycle exercisers, and in particular the crank mechanism used with those exercisers, pertains to the length of stroke. The stroke length is determined by the length of the crank arms used in the crank mechanism, and this length is not readily changeable. Changing the effective stroke length requires either replacing the entire crank assembly, or providing crank arms having variable positions for attaching the pedals on the crank arms. In either case, these alternatives are expensive and require the service of a technician to modify the length of the crank arms for users having significantly different lengths of stroke, namely, shorter or longer legs, or those of substantially different athletic ability.