Why is it more gentle to your joints than a terrestrial stationary bicycle?
buoyancy
The effect of gravity is reduced by 50% if submerged to the waist, 75% at the chest and 90% at the neck. AquaBiking is good therapy for all lower body joint injuries, including professional athletes.
Another good therapeutic exercise is squats in waist-high water. As one goes through the range of motion from waist to neck, buoyancy counteracts total weight-bearing by 50% to 90% of body weight. The effect of buoyancy is smallest when the knees and ankles are least flexed and greatest when the knees and ankles are most flexed. This is therapeutic for persons with joint injuries that have greater sensitivity to pain and likelihood of re-injury with the degree of flexion. Additional weight can vary from a simple weightless dowel to a 45-pound bar and four 45-pound plates.