A spring-based mechanism for saving labor of a bicycle rider is disclosed and in one embodiment includes an axle operatively connected to a chain wheel and a first set of bearings via a gear assembly; a housing for mounting a shaft therein wherein the first set of bearings is provided at one end of the shaft; a second set of bearings provided at the other end of the shaft; a spring in the housing and having one end attached to one end of the shaft and the other end attached to the other end of the housing; and a clutch provided externally of the other end of the housing, the clutch being operatively connected to the second set of bearings and including a lock lever. The mechanism can store elastic force by counterclockwise pedaling and release the stored energy by disengaging a clutch from the mechanism when riding uphill.