Stop and get medical help
If you get chest pain or pressure, feel faint or dizzy, are unusually breathless, or your heart races or beats irregularly during exercise, as our plans advise. The American Heart Association says these need immediate medical evaluation.
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Call 999 (911 in the US)
For chest pain that feels tight, heavy or squeezing, or spreads to your arms, neck, jaw or back; a sudden, extremely painful headache, especially while straining; someone who faints while exercising; or palpitations that don't go away, or come with chest pain, breathlessness or feeling faint. Don't drive yourself to A&E.
Also call 999 for pain and swelling in one leg with breathlessness or chest pain: it can be a blood clot that has reached the lungs.
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A headache with effort
Ask for an urgent GP appointment or get help from NHS 111 for a headache that's triggered or made worse by coughing, sneezing, bending down or exercising.
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Light-headed after you step off
Slow down for the last few minutes and hold the rails to step off. See a GP after any faint, and if you keep feeling light-headed after slowing gradually, or dizziness keeps coming back.
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Your knee
Get advice from NHS 111 now: you cannot move the knee or put any weight on it, or it is very painful, badly swollen or has changed shape; or the knee locks, gives way or clicks painfully. Painless clicking is normal.
See a GP or physiotherapist if knee pain hasn't improved within a few weeks, or if your knee gives way on the stairs, as our knee pain on stairs guide says.
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Your calf or heel
Same day (NHS 111): throbbing pain and swelling in one calf or thigh, with warm, red or darker skin around it, which can be a blood clot in a leg vein; or a snap or pop at the back of the heel, then trouble walking or standing on tiptoe.
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Your lower back
Call 999 or go to A&E: loss of feeling or numbness around the genitals or bottom, new trouble peeing or controlling your bladder or bowels, changes in genital sensation during sex or problems with erections or orgasm, or pain, tingling, weakness or numbness in both legs. These are signs of cauda equina syndrome, which needs treating in hospital urgently. Don't drive yourself.
Call 999 or go to A&E: back pain with chest pain, or back pain that started after a serious accident, such as a car crash.
See a GP if pain spreading down a leg hasn't improved after a few weeks of home treatment, is getting worse or stops your normal activities. Sciatica on both sides, or weakness or numbness in both legs that's severe or getting worse, is a 999 call or a trip to A&E.
Aim for discomfort you'd call mild to moderate, no more than about 5 out of 10. It should settle within an hour or so, and your back should be no worse the next morning, as our back pain guides say. Pain, pins and needles or numbness spreading down a leg are the exception: stop, and see our sciatica guide.
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A hernia
See a GP if you think you have a hernia, a bulge or lump that may get bigger when you strain and smaller when you lie down. Get help from NHS 111 if you have a hernia and pain in or around it, a bloated tummy, you feel or are sick, you're vomiting blood or your vomit looks like coffee grounds, you're constipated, you have a high temperature or feel hot, cold or shivery, or you've suddenly become confused. Call 999 or go to A&E for a femoral hernia (a small lump at the top of your thigh, in your groin) with very bad tummy pain, sickness, being unable to fart or poo, a high temperature or sudden confusion.
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Before you start
Speak to your GP first if you haven't exercised for some time or have medical conditions or concerns, as the NHS advises. Get advice before hard or straining work if your blood pressure is uncontrolled (140/90 or higher at a clinic, or 135/85 at home), or you have heart disease or chest pain when you're active, a pacemaker or defibrillator, diabetic eye disease, glaucoma, a hernia, recent eye or tummy surgery, or you're pregnant, as our breathing guide lists.
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Sore, or hurt?
Muscle soreness for a day or two after a new or harder session is common and fades. Sharp pain, or pain that builds during a set or lingers into the next day, isn't: swap to an easier version, and see a clinician if it persists, as our plans advise. The NHS says to stop exercising straight away if you feel any pain or become unwell, and to get help from 111 if symptoms worry you or don't go away.
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