An ergonomic saddle structure for bicycles and pedal machines comprises a shell (2) made of relatively rigid material, a pronged connection (15) anchorable on the lower part to the shell (2) and having a central body (16) with a slotted through hole (23) provided with flared or smoothed longitudinal edges (23′), connection means which comprise a fork (24) with a pair of lateral wings (25, 26) adapted to house the central body (16) and provided with respective cylindrical through openings (27, 28) as well as locking means for locking the fork (24) with respect to the pronged connection (15), which means comprise a first pair of inserts (30, 31) insertable in one portion of the through openings (27, 28), a second pair of inserts (39, 40) insertable in the remaining portion of the circular through openings (27, 28), are first screw means (37) operating on the first pair of inserts (30, 31) and second screw means (43) operating on the second pair of inserts (39, 40) in order to longitudinally and angularly lock the pronged connection (15) with respect to the fork (24).