An exercise device upon which a user generally standing upright supported by foot platforms suspended from a frame via linkages in which the linkage lengths and pivot points correspond generally to the users upper and lower legs and hip and knee joints. This device not only allows natural free and spontaneous leg movement, able to simulate such exercises as walking, jogging, running, stepping, skiing or gliding, bicycling, climbing, reverse action and various isolated leg exercises, where the exercises can be performed at random generally without the need to reconfigure the device. This device preferably includes an isolation system capable of simulating natural forces throughout the entire range of movement in the horizontal and/or vertical plane. A safety/suspension system can be provided, alone or in combination with the isolation system, to resist sudden foot movement in the same direction, yet allows a slow and controlled tilting of the linkages whereby the user may simulate uphill and downhill travel.