What should you know about rhabdomyolysis after flu?

Rhabdomyolysis means that muscle cells are breaking down and releasing their contents into the bloodstream. An infection, fever, dehydration, prolonged immobility, or a return to intense exercise while recovering may place extra stress on muscles. Flu-like illness can also cause ordinary body aches, so the pattern and severity matter.

Warning features include pain that is severe or out of proportion, muscle swelling, pronounced weakness, cramps, dark or tea-coloured urine, or passing much less urine. Compare ordinary exercise soreness with the guidance on [Muscle Soreness After Exercise](/symptoms/muscle-soreness-after-exercise/), while remembering that illness-related symptoms deserve medical attention.

Rest from strenuous exercise and contact a clinician the same day if concerning muscle symptoms develop during or after flu. Mention fever, vomiting, diarrhoea, poor fluid intake, new medicines, recent exertion, and the timing of the muscle pain. Do not restart hard training until a clinician has assessed the symptoms.

Medical assessment may include examination plus blood and urine tests to look for muscle injury, kidney stress, and changes in body salts. Sip fluids if you can do so safely, but do not delay care while trying to manage severe symptoms at home.

Go to emergency care for dark urine, very little urine, severe weakness, rapidly increasing muscle swelling or pain, confusion, fainting, chest pain, breathing difficulty, seizures, or inability to keep fluids down. These symptoms can worsen quickly and need prompt evaluation.

Could my muscle symptoms be more than ordinary flu aches? Do I need blood or urine testing? Which medicines, fluids, and activities should I avoid, and what signs mean I should return urgently?