US Patent 7163493 Treadmill having changeable suspension

A treadmill includes a tread deck supported on a tread base, and one or more cushioning members disposed below and engaged with the tread deck for cushioning the tread deck and for absorbing impact loads imparted on the tread deck by the users, the cushioning member includes different resilience for applying different cushioning force onto the tread deck when the cushioning member is rotated relative to the tread base. A rod is disposed in the tread base for supporting the cushioning members. One or more gears may be attached to the rod and engaged with a rack of the tread base for rotating the rod and the cushioning members relative to the tread base when the rod and the gear are moved relative to the rack.