CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/001,290, filed May 21, 2014, the disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an underwater (aquatic) exercise cycle with an improved transmission that provides either fixed or adjustable smooth pedal resistance, that is not dependant on water resistance like common aquatic exercise cycles. 
       BACKGROUND OF THE INVENTION 
       [0003]    Underwater cycling is becoming more popular as a tool for exercise and rehabilitation. The benefits of underwater workouts are well known and can be less stressful alternatives to traditional workouts. People may be averse to traditional workout methods due to age, joint problems, or mobility issues. While swimming in water is known to be a great low-impact exercise, not everyone can swim. Therefore, riding an exercise cycle in a pool is an excellent alternative because one can receive workout/rehabilitation benefits, but with the lower stress of moving in water. Health care providers often recommend aquatic physical therapy because it allows one to move more freely with decreased pain. Water has a therapeutic effect on muscles allowing them to relax and increase flexibility. Also warm water increases blood flow, which enables faster healing. 
         [0004]    Existing underwater exercise cycles use water resistance. While water resistance may be effective in achieving a desired workout, variations of resistance is limited. 
         [0005]    Additionally, water resistance can cause less smooth pedaling due to a lack of a flywheel/inertia, which is undesirable for the goal of lowering any impact involved in the exercise. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an objective of the present invention to provide an easy to use underwater exercise cycle that incorporates a flywheel transmission with either fixed tension, or with manual tensioning means to provide for improved underwater exercise/rehabilitation that allows the user to experience smoother and more continuous rotation with multiple distinct levels of resistance. 
         [0007]    One embodiment of the invention comprises a foldable cycle frame with a an adjustable seat, handlebars, pedals attached to a drive gear affixed to a drive shaft, a flywheel having an integrated gear that rotates independently on the same drive shaft, a separate secondary gear having two gears of different diameters attached to a second shaft, which is parallel to the drive shaft, in which the smaller secondary gear meshes with the drive gear and the larger secondary gear meshes with the flywheel gear to obtain a fixed ratio of pedal rotation to flywheel rotation, and further comprising a flywheel tensioning means that allows the user to easily and quickly select various levels of pedal effort while in motion. 
         [0008]    Another embodiment of the invention comprises an underwater exercise cycle using a compact flywheel transmission with fixed resistance. 
         [0009]    Yet another embodiment of the invention comprises a semi-recumbent attachment that provides side handlebars and a backrest, which allows the user to sit upright with the back supported. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of the invention showing a foldable bike frame with a direct gear flywheel transmission with a tensioning means to adjust frictional forces applied to the flywheel.  FIG. 2  is a close-up perspective view of the flywheel transmission and tensioning means.  FIG. 3  shows a “semi-recumbent” version of the cycle. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    An aquatic exercise cycle, transmission and tensioning means are shown generally in  FIGS. 1 and 2 . The aquatic exercise cycle comprises a stainless steel folding frame  1 ,  2  including an adjustable seat  3 , a handlebar  4 , a crank and gear multiplier  5 ,  6 , an energy storage device in the form of a flywheel  7 , a resistance system  8  with a resistance adjustment mechanism  9 , and with integrated wheels for transportation  10 . Alternatively, the folding frame  1 ,  2  could be made from plastic, composite or any other suitable material for an aquatic environment. Additionally, the handlebar  4 , could be made adjustable. The gear multiplier  6  is made from multiple plastic and corrosion-resistant metal components such, which are compatible with the aquatic environment. Alternatively the gear multiplier  6  could be made from multiple ceramic, composite or other components of suitable materials. The resistance system  8  incorporates a belt and tensioners to mechanically adjust the level of resistance at the crank. The resistance is adjustable through multiple discreet settings, selected with the tension-adjustment knob  11 . 
         [0012]    The crank and gear multiplier  5 ,  6  comprises a stainless steel drive shaft  12  rigidly connected to the main gear  13 , which drives the secondary gear  14 , which rotates on its own secondary shaft  15 . The secondary gear  14  comprises two integrated gears of different diameters  16 ,  17 ; the smaller gear  17  driven by the main gear  13  turns the larger secondary gear  16 . The larger secondary gear  16  drives a small gear integrated to the flywheel  7 , driving (spinning) the flywheel at a fixed ratio. The flywheel and integrated gear  7  spin freely on the drive shaft  12 . 
         [0013]    The resistance system  8  comprises a tension belt  18 , a fixed tension pulley  19 , a floating tension pulley  20 , a tension bar  21 , a tension adjustment rod  22  and a tension adjustment sleeve  23 . The tension belt  18  fits in a groove in the flywheel  7  and also over grooves in the fixed  19  and floating  20  tension pulleys. The floating tension pulley  20  is connected to the tension bar  21 . The fixed tension pulley  19  rotates on a shaft connected to the main frame  2 . Alternatively, the tension pulleys  19 ,  20  could be both fixed or floating. The tension bar  21  slides up-down through the tension adjustment sleeve  23 , which is rigidly attached to the main frame  2 . The tension adjustment rod  22  rigidly connects the tension bar  21  to the tension adjust knob  11 . Alternatively, the tension adjustment rod  22 , could be made from a flexible cable, instead of a rigid component. Turning the tension adjust knob  11  pulls on the tension adjust rod  22 , which pulls on the tension bar  21 , which in turn pulls the floating tension pulley  20  up and increases the tension on the tension belt  18 . The resistance adjustment mechanism  9  consists of a tension-adjust rod  22 , an upper  24  and lower  25  housing, an index-ring  26 , an outer  27  and inner  28  hub, two (2) compression springs  29 , two (2) steel balls  30 , and a shaft  31 . The tension-adjust rod  22  connects to the tension-adjust inner hub  28 . The inner hub  28  turns with the outer-hub  27 . The outer-hub  27  has a shaft with square-flat sides, which couple to the tension-adjust knob  11  and the index-ring  26 . The upper-housing  24  has two holes for the tension-adjust springs  29  and the steel balls  30 . The index-ring  26  sits on top of the spring-compressed steel balls  30  and has a series of hole-perforations which the steel balls  30  engage, resulting in discreet tension settings. Alternatively, the steel balls  30  could be made from plastic, ceramic, or other suitable material and the number of balls ( 2 ) could be less or more, depending on what is required to sufficiently keep the tension-adjust knob in its set position. When the tension-adjust knob  11  is rotated it rotates the index-ring  26 , the outer-hub  27  and the inner-hub  28 . As the inner-hub rotates it pulls on the tension-adjust rod  22  increasing tension on the tension-belt  18 . The index-ring  26  rotates until the steel balls  30  fit into the next hole-perforation, held in place by the force of the tension-adjust springs  29  for each tension setting. The rotating parts rotate on the tension-adjust shaft  31 . The tension-adjust shaft  31  has a shaped, splined or tapered end that fits into the lower tension-adjust housing  25  preventing the shaft from rotating. 
         [0014]      FIG. 3  shows a “semi-recumbent” version of the aquatic exercise cycle. This option includes side-side handlebars  32  and a backrest  33 . This optional assembly converts the conventional-styled aquatic exercise cycle from a conventional to a semi-recumbent style. 
         [0015]    The present invention has been described with reference to preferred embodiments, however those skilled in the art may recognize that changes may be made without deviating from the scope of the present invention. Further the flywheel transmission and tensioner may be used by other exercise devices such as treadmills, elliptical trainers, etc.
An underwater exercise cycle that improves on existing designs through the use of a compact flywheel transmission with adjustable resistance. The invention allows for smooth and continuous pedaling across a range of distinct levels of resistance, thereby enhancing comfort, low-impact, and effectiveness of aquatic exercise.