Exercise is classically associated with muscular soreness, presenting one to two days later, delayed onset muscular soreness. Blood muscle enzymes and protein elevations are characteristic, and may cause renal failure. Creatin phosphokinase peak appears on the fourth day and depends on exercise type and individual parameters. This effect is attenuated with repeated bouts, by habituation. Metabolic complications are rare. The knowledge of this reaction, even with common exercises, allows to postpone investigations for a complex metabolic disorder, or to avoid stopping a medication for fear of a side effect, as with statins. Indeed, it is necessary to wait for seven days without any exercise before interpreting an elevated CK result.