A 23 year old male kick boxer presented with a 24 hour history of pain and being unable to extend the interphalangeal joint of the left thumb. There was no history of trauma or any other risk factor for spontaneous rupture of the extensor pollicis longus tendon. On the previous day, he had been doing reverse press ups on the dorsum of his hands with his wrists hyperflexed as part of his training for kick boxing. At operation the extensor pollicis longus tendon was found to be divided at the level of the dorsal tubercle of the radius and was not directly repairable. The treatment was an extensor indicis proprius transfer. We suggest that the cause of the tendon rupture was direct pressure on the dorsal tubercle of the radius sustained while performing reverse press ups.