An endless cord exercise machine in which a user applies a continuous pulling motion to a cord that is attached to a resistance mechanism is disclosed. The machine may be arranged to simulate the acts of rope climbing or of scaling a wall with the assistance of a rope, or may be arranged to provide other types of upper and lower body muscle development. The resistance mechanism is ideally comprised of a plurality of rotary viscous dampers of differing viscosities housed in a rotating drum. A spring-loaded adjustment key mechanism extending through the hub of the drum and dampers allows the user to selectively engage any combination of dampers to provide exercise resistance.