Elongate sickle knife

A header for an agricultural vehicle, the header comprising:

• a header frame having a leading edge;
• and
• an elongate sickle knife mounted along the leading edge of the header frame;
• an actuator for reciprocally moving the elongate sickle knife in its longitudinal direction relative to the header frame between a first position and a second position over an intermediate position;
• and
• at least one accumulator extending between the header frame and the elongate sickle knife to accumulate energy during a first movement of the elongate sickle knife from the intermediate position towards at least one of the first position and the second position, the at least one accumulator accumulating energy at all times during the first movement, wherein the actuator decelerates the sickle knife and during deceleration energy is accumulated in the at least one accumulator, and to release accumulated energy during a second movement of the elongate sickle knife opposite the first movement.