Too much exercise can cause muscle breakdown

Last week, 13 University of Iowa football players were hospitalized for a condition known as rhabdomyolysis. This condition results from an extreme breakdown of muscle fibers and complications caused by the circulation of the breakdown products.

Rhabdomyolysis generally results from muscle injury. Trauma is typically the most common cause of rhabdomyolysis. Other causes include genetic conditions, dehydration, medications, supplements, seizures, heatstroke, vascular insufficiency, severe exertion or any combination of these.

There are two types of muscle, smooth or involuntary muscles and striated or voluntary muscles. Muscles consist of a complex system of filaments that contract and relax in response to impulses from the nervous system.

Striated muscles are the engines that drive the movement of joints. Like all engines they rely on a fuel source to continue working. If the demand placed on muscles exceeds the availability of nutrients, the fibers “lock up” and cramp. If the imbalance continues, muscle fibers begin to break down.

When muscles break down, proteins and enzymes are released into the bloodstream. Among these enzymes is creatine kinase (CK). The concentration of CK can be measured in a blood sample and indicates the degree of muscle breakdown. CK also appears in various forms that indicate what types of muscles have been injured.

In rhabdomyolysis, myoglobin is among the breakdown products. When high concentrations of this protein are emitted, urine develops a reddish discoloration. If high levels persist, kidney failure will result.

Treatment consists of intravenous infusion of fluids and renal dialysis if necessary.

In the case of the Iowa athletes, it is believed that extreme exertion as part of an offseason workout was the cause. One player reported having to perform 100 squat repetitions with 240 pound weights.

Physical exercise is a big step toward good health, but as 13 Iowa football players have discovered, moderation is essential.