Human-robot cooperation is increasingly demanded in industrial applications. Many tasks require the robot to enhance the capabilities of humans, allowing them to execute onerous tasks or improving their functionalities. Besides wearable robotics, standard industrial manipulators are common solutions adopted to empower humans. With this aim, the paper describes a fuzzy-impedance control approach for assisting human operator in onerous industrial applications. The developed method allows to set in realtime the set-point of impedance controller based on human intentions. Two fuzzy membership functions have been defined, respectively, on the basis of interaction force derivative and robot velocity signals, allowing to calculate the needed assistance level for the human operator. The effectiveness of proposed approach is verified on KUKA iiwa 14 R820 in an experimental procedure where human subjects evaluate the robot's performance in a collaborative lifting task.