An exercise machine for performing leg curl and leg extension movements includes: a frame configured to rest on an underlying surface; an upper leg-supporting assembly pivotally interconnected with the frame, the upper leg-supporting assembly having a seat pad; a torso-supporting assembly pivotally interconnected with the frame and with the upper leg-supporting assembly, the torso-supporting assembly having a backrest pad; a leg curl assembly arm pivotally interconnected with the frame about a first pivot axis; a leg extension assembly arm pivotally interconnected with the frame about a second pivot axis; a resistance-imparting unit coupled with the leg curl movement arm and the leg extension movement arm; and a conversion mechanism interconnected with the frame and/or the torso-supporting assembly and the upper leg-supporting assembly. The conversion mechanism moves the torso-supporting assembly and the upper leg-supporting assembly between a leg extension position, wherein the seat pad and the backrest pad combine to form a backrest and seat for a seated exerciser, and the second pivot axis is positioned in front of a front edge of the seat pad, and a leg curl position, wherein the seat pad and backrest pad combine to form a curl platform for a prone exerciser, and the first pivot is positioned above a plane defined by an upper surface of the seat pad.