Stop and get medical help
For chest pain or pressure, unusual breathlessness, dizziness or fainting, or a racing or irregular heartbeat during exercise, as our plans advise. The American Heart Association says these need immediate medical evaluation.
Source 21
Call 999 (911 in the US)
For sudden chest pain or discomfort that doesn't go away, pain that spreads to your arms, neck, jaw, stomach or back, or chest pain with sweating, feeling sick, light-headedness or breathlessness; someone who faints while exercising; palpitations that don't go away, or come with chest pain, breathlessness or feeling faint; a headache that starts suddenly and is extremely painful; or the signs of a stroke, even if they've stopped. Don't drive yourself to A&E.
Sources 23, 24, 25, 26, 27, 28
Feeling faint or sick after a hard push
Stop, sit or lie down, and breathe normally, as our breathing guide advises. If someone faints while exercising, call 999.
Source 25
Muscle breakdown after a big session
Same day (call NHS 111, or go to A&E if you feel very unwell): after a big or unusual session, such as a first sled session or many heavy pushes, muscle pain, swelling or weakness far worse than the session explains, and dark pee (red, brown, tea or cola coloured), sometimes starting hours or days later. Dark pee isn't always there, so muscles far sorer, more swollen or weaker than the session explains still need the same-day check. It can be rhabdomyolysis, a breakdown of muscle that can harm the kidneys. Call 999 for sudden, severe pain in a swollen, tight muscle, as our pain guides advise.
Sources 29, 30, 31
A snap at the back of your heel or calf
Same day: a sudden snap or pop at the back of the heel or calf, or a feeling of being kicked there, then walking flat-footed and being unable to push off or stand on tiptoe. It could be an Achilles tendon rupture: go to A&E or a minor injuries unit, or contact NHS 111, as our Achilles rupture guide says. Calf or leg pain or swelling with breathlessness or chest pain is a 999 call.
Your knees or back
Get advice from NHS 111 if your knee is very painful, you can't put weight on it, it's badly swollen or has changed shape, or it locks or gives way. Call 999 or go to A&E for back pain with pain, tingling, weakness or numbness in both legs, loss of feeling around your genitals or bottom, new trouble peeing or controlling your bladder or bowels, or changes in genital sensation during sex.
Sources 32, 33
A slip or fall
Call 999 or go to A&E if you heard a crack, or the injured part has changed shape, points at an odd angle, is numb or tingling, or has turned blue, grey or cold. Get help from NHS 111 if it's very painful, badly swollen or bruised, or you can't put weight on it.
Source 34
A hernia
See a GP if you think you have a hernia, and get help from NHS 111 for pain in or around it. Call 999 or go to A&E for a femoral hernia (a lump at the top of the thigh) with very bad tummy pain, being sick, being unable to fart or poo, a high temperature or sudden confusion.
Sources 35, 36
Check before you start
If you haven't exercised for some time or have a medical condition, speak to your GP first, as the NHS advises. Check with your GP before hard intervals if you're inactive and have heart, metabolic or kidney disease, or symptoms when you're active, as our HIIT guide says.
Source 37