Exercise intolerance

Exercise intolerance means a reduced ability to carry out physical activity at the level you would expect for your age and fitness — becoming breathless, exhausted, weak or unwell sooner than normal, or noticing that activities you once managed easily now leave you struggling. Delivering oxygen and energy to working muscles depends on a chain: the lungs taking in oxygen, the blood (and enough haemoglobin) carrying it, the heart pumping it, the circulation delivering it, and the muscles and their metabolism using it. A weak link anywhere along that chain shows up as exercise intolerance, which is why it is such a common but non-specific symptom. Being unfit or overweight is a frequent and reversible cause. But a genuine, persistent or worsening reduction can point to anaemia (too little oxygen-carrying capacity), heart problems such as heart failure or coronary disease, lung conditions, an under- or over-active thyroid, poorly controlled diabetes, and, less commonly, muscle or metabolic disorders. The accompanying symptoms are the clue: breathlessness and ankle swelling point to the heart; breathlessness and wheeze to the lungs; tiredness and pallor to anaemia; and muscle pain or weakness to a muscle cause. A meaningful, unexplained decline in what you can do is worth taking seriously.

• Being out of condition or overweight — a common, reversible cause that improves with gradual training.
• Anaemia — too few red cells to carry oxygen; tiredness, breathlessness and pallor.
• Heart conditions — heart failure or coronary disease; breathlessness, ankle swelling, chest tightness on exertion.
• Lung conditions — asthma, COPD or others; breathlessness and wheeze.
• Thyroid problems — an under- or over-active thyroid.
• Poorly controlled diabetes, or muscle and metabolic disorders — less common, with muscle pain or weakness.

Because exercise intolerance can arise anywhere along the oxygen-delivery chain, the assessment is guided by the accompanying symptoms and examination. Helpful blood tests include a full blood count for anaemia, thyroid function (TSH) for an over- or under-active thyroid, glucose or HbA1c for diabetes, and, where the heart is a concern, NT-proBNP; kidney and liver function and electrolytes give a broader picture. If a muscle cause is suspected, creatine kinase is checked. Tests of the heart and lungs (such as an ECG, echocardiogram or lung-function tests) are often central. Mediora.AI can surface anaemia, a thyroid abnormality, a raised cardiac marker or a metabolic pattern on your results that may explain reduced exercise tolerance; interpreting these alongside the heart and lung assessment belongs with your doctor.