A vehicle seat having a bottom frame, a seat back connected to the frame, and an armrest capable of upward and downward movement. The armrest includes a seat bracket connecting the armrest to the frame and a vertically variable adjustment mechanism. The mechanism has a control disposed in the armrest, a lock actuated to an engaged or disengaged position by the control, a rack disposed in a generally vertical direction, and a one-way bearing acting as pinion and having two rotational states. The first rotational state is a locked state where the lock is engaged and prevents the one-way bearing from rotating, preventing the rack and armrest from a downward movement. The second rotational state is a free state where the lock is in the engaged position and a force is applied in the upward direction, the one-way bearing can rotate, allowing the rack and armrest an upward movement.