A resistance unit for an exercise device, such as a bicycle trainer, includes a magnetic member which cooperates with a rotating electrically conductive member to establish eddy current resistance to rotation of a rotatable member forming a part of the resistance unit. The resistance unit includes a body to which the rotatable member is mounted, and an adjustment mechanism is interconnected with the magnetic member and the body for adjusting the position of the magnetic member relative to the electrically conductive member, to adjust the eddy current resistance experienced by the rotatable member. The magnetic member is movably mounted within a passage defined by the body, and the adjustment mechanism includes a manually operable actuator which is accessible from the exterior of the body. The actuator is rotatable relative to the body, and rotation of the actuator functions to move the magnetic member toward and away from the electrically conductive member, to adjust the eddy current resistance. The rotatable member is interconnected with a flywheel, and the electrically conductive member is mounted to and rotatable with the flywheel to apply resistance to rotation of the rotatable member through the flywheel.