Torsional force on round bars produces principal strains on the surface at 45 degrees to the axis of the bar. Dual element shear strain gages such as the Micro Measurements 187UV gages, bonded at diametrically opposite points on the bar will respond to these strains to give an output proportional to torque on the bar. A full bridge connection for the elements of the shear gages can be made on the bar, then lead wires can be taken to an instrument for measuring and recording the applied torque.
But if the bar is rotating , then wired connections between the gage and the instrument will be impossible. This video shows how a TECAT WISER telemetry system overcomes this problem , to measure and record the torque on the bar while it is rotating.