Header for an agricultural vehicle (1), wherein the header comprises a header frame (2) and an elongate sickle knife (3) mounted along a leading edge of the header, wherein the header further comprises an actuator (17, 18) for reciprocally moving said elongate sickle knife (3) in its longitudinal direction relative to the header frame (2) between a first position and a second position over an intermediate position, wherein accumulator means (12) extend between the header frame (2) and the elongate sickle knife (3) to accumulate energy during a first movement of said elongate sickle knife (3) from the intermediate position towards at least one of the first position and the second position, and to release accumulated energy during a second movement of said elongate sickle knife (3) opposite to said first movement.
