Sexual stimulation
Internal stimulation

The excitation-transfer theory states that existing arousal in the body can be transformed into another type of arousal. For example, sometimes people can be sexually stimulated from residual arousal arising from something such as exercise, being transformed into another type of arousal such as sexual arousal. In one study participants performed some physical exercise and at different stages of recovery had to watch an erotic film and rate how aroused it made them feel. They found that participants who were still experiencing excitatory residues from the exercise rated the film as more arousing than those who had fully recovered from the exercise. This suggests that the remaining arousal from the exercise was being transformed into sexual arousal without any external stimulation.
keywords:frequency