An ergonomic saddle structure, for bicycles or pedal operated machines, comprising: - a shell made of a relatively rigid material having a longitudinal axis and a total length; - connection means designed to anchor said shell to a seat post of a frame of a bicycle or pedal operated machine, said connection means having a predetermined maximum width; wherein said shell comprises a rear portion with an enlarged plan shape having a predetermined length and width and convex lateral edges ( 6, 7), a front portion with an at least partially tapered plan shape and a front edge portion ( 4 ') and an intermediate connection portion with concave lateral edges ( 13, 14) uniformly joined to the convex lateral edges ( 6, 7) of said rear portion, wherein said intermediate connection portion has a minimum width just greater than the maximum width of said connection means; characterized in that the convex lateral edges ( 6, 7) of said rear portion have a substantially constant curvature and a predetermined average bend radius, the concave lateral edges ( 13, 14) of said intermediate connection portion having a bend radius about equal to the average bend radius of the convex lateral edges (6, 7) of said rear portion and a center of curvature placed at a distance from said front edge portion ( 4 ') about equal to the distance of said minimum width of said intermediate connection portion from said front edge portion ( 4 '), in such a manner to define at the user's inner thigh a narrow zone adapted to reduce the compression and rubbing of the inner thigh with respect to said lateral edges ( 13, 14) of said intermediate connection portion, thereby increasing the comfort and efficiency of the pedal stroke. - a shell made of a relatively rigid material having a longitudinal axis and a total length; - connection means designed to anchor said shell to a seat post of a frame of a bicycle or pedal operated machine, said connection means having a predetermined maximum width; wherein said shell comprises a rear portion with an enlarged plan shape having a predetermined length and width and convex lateral edges ( 6, 7), a front portion with an at least partially tapered plan shape and a front edge portion ( 4 ') and an intermediate connection portion with concave lateral edges ( 13, 14) uniformly joined to the convex lateral edges ( 6, 7) of said rear portion, wherein said intermediate connection portion has a minimum width just greater than the maximum width of said connection means; characterized in that the convex lateral edges ( 6, 7) of said rear portion have a substantially constant curvature and a predetermined average bend radius, the concave lateral edges ( 13, 14) of said intermediate connection portion having a bend radius about equal to the average bend radius of the convex lateral edges (6, 7) of said rear portion and a center of curvature placed at a distance from said front edge portion ( 4 ') about equal to the distance of said minimum width of said intermediate connection portion from said front edge portion ( 4 '), in such a manner to define at the user's inner thigh a narrow zone adapted to reduce the compression and rubbing of the inner thigh with respect to said lateral edges ( 13, 14) of said intermediate connection portion, thereby increasing the comfort and efficiency of the pedal stroke.