Men noticing their penis appears smaller during or after a workout may be seeing a temporary change in its flaccid appearance rather than an actual reduction in size. The phenomenon has recently been dubbed ‘gym penis’ online, with the terms referring to temporary retraction of the penis and scrotum during or after strenuous exercise. While ‘gym penis’ is not a medical diagnosis, temporary changes in penile appearance are well established. Cleveland Clinic urologist Dr Raevti Bole explains that a range of factors can affect how large the penis appears, with some changes lasting only a short time. The NHS advises men to seek medical advice if they notice changes to the appearance of their penis that do not go away.