Playing with your children or meeting a friend for coffee are everyday activities that many people move between without giving much thought to how much mental or physical energy they take.

For many people living with long COVID, things are different. Reading, working at a computer or concentrating on a conversation can require far more effort than it once did, and mental fatigue can make it difficult to keep going.

Fatigue is one of the most common symptoms of long COVID, also known as post-COVID condition. For some people it improves over time. For others it can persist for months or years, interfering with work, family life and social activities.

Scientists are still trying to understand what drives this exhaustion. Research has pointed to several possible biological processes, including changes in the immune system and nervous system. No single explanation has emerged, and different mechanisms may contribute in different people.

Our new study offers another clue. We found lower blood flow in the brains of people with long COVID who experienced persistent fatigue. These differences were also related to........

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