Rhabdomyolysis, also known as tying-up, azoturia or monday morning disease is a serious disorder of muscular tissue. It results from a breakdown of muscle fibers and release of their contents into the bloodstream. This can lead to complications such as kidney failure.

It is caused by muscle cells working without oxygen (anaerobically) and building up excessive amounts of 'waste' products such as lactic acid, that can damage the cells and lead to their disintegration. The lack of oxygen supply to the muscles is either due to an inadequate blood supply or to great exertion. Many other predisposing and trigger factors are thought to be involved in this complex disorder, including genetic factors, nutritional factors (excessive carbohydrates, electrolyte imbalance), hormonal imbalances, lack of fitness, environmental conditions (cold, wet weather), etc.