Several medieval commentators on De caelo II, 7 investigate the question of whether local motion causes heat. I analyse the theories of Averroes, Albert the Great, Thomas Aquinas, Peter of Auvergne, John of Jandun, John Buridan and Nicole Oresme and two anonymous theories. Although all of these authors agree that local motion generates heat, each of them presents his own explanation of the heating effect of motion. Averroes, Thomas Aquinas, John of Jandun and John Buridan argue that motion is the per se cause of heat. Their explanations of the heating effect of motion are based on metaphysical considerations such as the relation between a subject and its characteristics or perfections and the causal order in a genus. Albert the Great, Peter of Auvergne, Nicole Oresme and the anonymous commentators, on the contrary, defend the thesis that motion is the accidental cause of heat. Their explanations refer to physical processes caused by motion.