What should you know about causes of muscle fatigue?

Fatigue may feel like heaviness, reduced stamina, or difficulty repeating an effort. A sudden change after exercise can reflect temporary overuse, while ongoing fatigue may relate to sleep, mood, food intake, hydration, or a recent illness such as [COVID-19](/conditions/covid-19/). [Dehydration](/conditions/dehydration/) can reduce exercise tolerance.

Other contributors include [Anaemia](/conditions/anaemia/), which can reduce oxygen delivery, and [Coeliac Disease](/conditions/coeliac-disease/), which may affect nutrient absorption. Burnout, alcohol-related health problems, [Chronic Kidney Disease](/conditions/chronic-kidney-disease/), and [Chronic Fatigue Syndrome](/conditions/chronic-fatigue-syndrome/) have different patterns and need separate assessment. Fatigue alone cannot identify one of these conditions.

Track when fatigue occurs, which muscles are affected, sleep quality, meals, fluid intake, activity, illness, and medicines. Reduce an unusually heavy workload temporarily, then return to activity gradually as tolerated. Eat regular balanced meals and replace fluids after sweating or illness. Arrange a GP review if symptoms continue, limit ordinary tasks, or recur without a clear trigger. A clinician may examine strength and choose tests based on the pattern rather than ordering every test for everyone.

Seek urgent help for sudden one-sided weakness, facial drooping, trouble speaking, severe breathlessness, chest pain, fainting, confusion, or inability to stand. Get prompt advice for steadily worsening weakness, difficulty swallowing, dark urine after intense exertion, or fatigue with unexplained weight change, bleeding, or persistent fever.

Is this true muscle weakness or reduced energy? Could sleep, nutrition, infection, anaemia, kidney health, alcohol, or medicines be involved? Which tests fit my symptoms? How should I pace activity while being assessed?