A telescopic crane arm including a boom with a bearing area for a boom extension, a boom extension movable out of and into the bearing area of the boom by travel movements so that a tip of the boom extension protrudes more or less far from the boom. The boom extension has a body at least partially in the form of a hollow profile, and a supply line is configured to simultaneously transmit both electrical energy and data signals. The supply line runs from the boom via the hollow profile of the boom extension to or at least in the vicinity of the tip of the boom extension, and is mounted and configured such that the supply line follows the travel movements. A mechanical tensioning device holds the supply line under mechanical tensile stress during the travel movements.