A rail system for an exercise machine which may be efficiently manufactured with different dimensions to suit different exercisers and exercise spaces. An exemplary embodiment includes a first rail, a second rail, a carriage movably connected to the first and second rails, at least one biasing member or elongated member adapted to be directly or indirectly connected to the carriage, and one or more spacers extending between the first and second rails. A lower member is connected between the rails beneath the spacers so as to enclose the space between the rails. The lower member includes a plurality of dividers defining channels in which elongated members or biasing members may extend. The spacers, rails, and lower member form a monorail configuration. The effective width of the monorail may be easily adjusted by simply using spacers having different widths, thus easing the manufacture of such exercise machines having different sizes.