Extremal control is an optimization performed by experimenting with optimised device directly during operation. On our department we deal with the extremal control of torsional oscillating mechanical systems by means of pneumatic flexible shaft couplings. The torsional stiffness of these couplings and so the natural frequencies of to rsional systems can be changed by adjusting the air pressure in their pneumatic flexible elements. The goal of this optimisation is to minimize the value of torsional vibration by changing the pressure of gaseous medium in the used pneumatic flexible shaft coupling. The goal of this article is to confirm the possibility of the use of extremal control in a laboratory torsional oscillating mechanical system built on our department.