The present invention provides a manually powered drive assembly for a vehicle. A foot crank winds a helical torsion spring through a system of shafts and sprockets in a first direction. By releasing a brake applied to a wheel, or wheels, of the vehicle, the wound spring transfers a rotational movement from a spring shaft to a freewheel sprocket coaxially aligned with the axle supporting a wheel, so that the rotational movement upon the wheel assists a user in manually moving the vehicle. The drive assembly may be advantageously used with a wheelbarrow to assist in building up momentum for moving heavy loads.