A gymnastic exercise machine (1a, 1b), particularly for anaerobic auxotonic muscle training, comprising a supporting footing that is provided with a movable frame that is associated with a folding seat, said movable frame being provided with lever means that can be actuated by a user located on said folding seat in order to move said movable frame with respect to said supporting footing with consequent folding of said folding seat in contrast with the action of the weight of said user, coarse adjustment means being provided and being associated with said movable frame in order to reduce or increase step by step the force required to actuate said lever means, fine adjustment means being provided associated with said movable frame in order to reduce or increase the force required to actuate said lever means, breaking down each step of the coarse adjustment means, characterized in that in a side elevation view said movable frame comprises: - a substantially L-shaped structure that is pivoted at one of its ends to a fixed structure that is integral with said supporting footing so as to have, in the inactive position, one side of said L-shape that is parallel and adjacent to said supporting footing and the other side of said L-shape that is substantially perpendicular to said supporting footing, - at least one adjustment arc, which is pivoted at one of its ends proximate to the other end of said substantially L-shaped structure so as to be directed toward said substantially L-shaped structure, said at least one adjustment arc being provided with a movable slider that can be positioned selectively along the longitudinal extension of said at least one adjustment arc and being pivoted to a first tension element that is pivoted to the end of a rocker-like rod that is pivoted at a central portion of itself to said side of said substantially L-shaped structure and has the other end pivoted to a link rod, which in turn is pivoted to said fixed structure at a height that is intermediate between the pivoting of said substantially L-shaped structure to said fixed structure and the corner of said substantially L-shaped structure, said at least one adjustment arc and said movable slider defining said coarse adjustment means. - a substantially L-shaped structure that is pivoted at one of its ends to a fixed structure that is integral with said supporting footing so as to have, in the inactive position, one side of said L-shape that is parallel and adjacent to said supporting footing and the other side of said L-shape that is substantially perpendicular to said supporting footing, - at least one adjustment arc, which is pivoted at one of its ends proximate to the other end of said substantially L-shaped structure so as to be directed toward said substantially L-shaped structure, said at least one adjustment arc being provided with a movable slider that can be positioned selectively along the longitudinal extension of said at least one adjustment arc and being pivoted to a first tension element that is pivoted to the end of a rocker-like rod that is pivoted at a central portion of itself to said side of said substantially L-shaped structure and has the other end pivoted to a link rod, which in turn is pivoted to said fixed structure at a height that is intermediate between the pivoting of said substantially L-shaped structure to said fixed structure and the corner of said substantially L-shaped structure, said at least one adjustment arc and said movable slider defining said coarse adjustment means.