A Massachusetts woman almost lost her leg after a life-threatening illness after a high-intensity spin course.

Kaelyn Franco said that she initially mistaken the symptoms of rhabdomyolysis as a sign that her training regiment was progressing well—until they turned into severe pain and swelling. In a TikTok video released last month that was viewed 3.5 million times, she shared a photo of her showing off her leg shape, with the caption "It’s not that I thought I gained muscle in a spin class."

The clip was then cut dramatically into an image of her lying on a hospital bed.

"It's not that I almost lost my leg and life the next day," she wrote.

In an interview with Today on Thursday, the 23-year-old woman explained that the doctor was pressing her leg to relieve stress and swelling. They subsequently diagnosed that she had rhabdomyolysis, also known as rhabdomyolysis.

According to the Centers for Disease Control, this condition “occurs when damaged muscle tissue releases proteins and electrolytes into the blood. These substances can damage the heart and kidneys and cause permanent disability or even death.” Experts say that strenuous exercise is also Will cause striated muscles, especially rotation courses "posed a risk to novices."

Franco is an avid cyclist. She said that when the weather started to get cold, she transferred to a spinning course. According to her cousin's recommendation, she attended her first class on September 15.

"I'm definitely pushing myself, but I don't think I overworked to the point where I wanted to. Well, I really did too much," Franco recalled.

"(But) as soon as I stepped on the bike, my knees softened and almost fell. At first I thought it was weird, but then I thought, maybe my muscles were tired, weak, and a little sore."

She said that her muscles felt "tight" the next day, but she brushed it off, which was a sign of her hard work. But as the symptoms worsened, Franco finally chose to go to the hospital: her pain was unbearable, she couldn't walk, and her urine became darker and darker.

Later tests showed that her blood contained a large amount of creatine kinase, an enzyme that can reveal muscle damage. Although the normal level is usually about 33-211 units per liter; Franco's CK level once reached more than 259,000.

"I can't walk or move, I have to plug in a catheter," she wrote in an Instagram post. "My striated muscle became acute compartment syndrome (a condition caused by pressure buildup caused by swollen tissue and internal bleeding)."

The doctor managed to save Franco's life and a leg through emergency surgery. More than two months later, she was still on crutches.

Franco, who was once very active, hopes that by December she will be able to move more freely. She said she wanted to disclose her experience to make sure that others knew the signs of striated muscle.

Symptoms include: muscle cramps, pain, feeling weak or tired, inability to complete work tasks or completing daily exercise, and brown urine.

"It really turned my world upside down," Franco told Today. "It's just super traumatic and stressful."