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ST. LOUIS, Mo. _ Moderation is the word of the week. This heat wave is unforgiving, especially for anyone who regularly workouts outdoors.

Washington University Emergency Medicine Specialist at Barnes-Jewish Hospital, Dr. David Tan, discusses a rare life-threatening condition that can occur from too much exercise.

Rhabdomyolysis, often caused by extreme exercise. It relates to overworked muscles and causing severe pain.

Spinning class

It occurs when people do not give their muscles time to adjust to an aggressive new exercise. When that happens they break apart and release compounds that can be harmful to the liver, such as a protein called myoglobin, which causes brown or tea-colored urine, a classic symptom of rhabdo.

While almost any intense activity can cause rhabdo, it almost always strikes people who are doing something new. Experts say that is why people should always progress from light to moderate and then vigorous intensity when doing a new exercise.