A 45-year-old man was referred by the internist because of a second episode of rhabdomyolysis. Motor milestones had been normal, and he had always been good at sports, although he was used to having stiff calves after skiing. At the age of 39 years he once experienced a sensation of ‘barbed wire’ in his upper legs, evolving in quite severe myalgia building up over days. This complaint dissolved in the course of three weeks. CK activity in this period increased to 23,094 U/L and normalized completely. There was no history of dark urine. In the absence of a metabolic cause or a history of the use of drugs, this was interpreted as having been caused by a viral infection. In the preceding months, he had been cycling fanatically daily, up to exhaustion. After this episode he had cut down on his sporting activities, but recently he had taken up mountain biking.