Two best friends in China found themselves in hospital, one in intensive care, after they challenged each other to perform 1000 squats while on a video call.
Tang, 19, told Chinese media that the pair were trying to see which one of them had better stamina, so launched into the extreme competition while chatting on video on July 10.
Tang, from Chongqing, and her friend from Guangdong did not exercise regularly before the contest and told Chinese media that the decision to test their fitness was made "spontaneously."
While both completed the challenge - dropping a leg-burning 1000 times - the pain set in days later.
Tang said that on the third day she began to feel unwell: "I didn't feel right as soon as I woke up. First of all, my legs felt achy and sore. What's more? I couldn't bend them.
"Afterwards, I went to the toilet and saw my urine was as dark as tea."
Tang's boyfriend took her to a local hospital where she was found to have a serious syndrome known as rhabdomyolysis which occurs when injured muscles release enzymes into the bloodstream.
Tang transferred to Chongqing Emergency Medical Centre before being moved to the Emergency Intensive Care Unit.
Doctor Li Ning told Chinese media that Tang's myoglobin level was higher than 3000 - a normal reading should be around 80.
He added that her level creatine kinase - an enzyme found in the heart and brain - was more than 11,000 times higher than it should be.
Tang reported that her friend was also hospitalised with the same condition.
Li issued a warning to the public not to exercise excessively.