Twelve Tufts University men’s lacrosse players were sent to the hospital and diagnosed with rhabdomyolysis following a workout with a Navy SEAL trainee last week.

The diagnosis, also called rhabdo, is a life-threatening condition that happens after an injury or overexertion, according to the Cleveland Clinic. 

“It’s very unusual to see that many people being hospitalized all at once with this condition, particularly young men who are presumably very physically fit,” Dr. Shruti Gupta of Brigham and Women’s Hospital recently told CBS Boston. 

Tufts says members of the team were diagnosed after a “voluntary, supervised 45-minute workout” on campus last Monday. The session, which included 50 participants, was led by a Tufts graduate who had recently completed Navy SEAL training. 

Seven of the athletes were treated in the emergency room and released. Five players remain in the hospital. 

Rhabdomyolysis causes and symptoms

Physiologist and anesthesiologist Dr. Michael Joyner says the condition can happen after very intense exercise — though it’s relatively uncommon. About 26,000 people in the United States develop it every year, the Cleveland Clinic estimates.

“What happens is the components of the muscle, especially something called myoglobin, which is red stuff that carries oxygen in the muscle leaks out and can attack the kidneys,” Joyner told CBS News. 

Symptoms of rhabdo include discoloration of your urine as well as swelling and soreness in the muscles, he said.

Cleveland Clinic adds people can also experience dehydration, decreased urination, nausea and loss of consciousness.

“Rhabdomyolysis symptoms can range from mild to severe,” the clinic’s website notes. “Symptoms usually develop one to three days after a muscle injury, though some people may not even notice muscle soreness.”

How to treat rhabdomyolysis

Treatments for rhabdomyolysis include receiving fluids and electrolytes through an IV, physical therapy and dialysis if a patient suffers a complication like severe kidney damage.

“If you don’t have any complications caused by rhabdomyolysis, you may feel better within a few weeks,” the Cleveland Clinic notes, adding a doctor may recommend waiting weeks to months before resuming exercise.

If a parent thinks their child might have rhabdo, start hydrating the child and get them to the emergency department, Joyner advised. 

“This is a potentially very challenging, dangerous thing and prompt treatment can really make a huge difference,” he said.