For how we live.
The stitch has a clinical name — exercise-related transient abdominal pain — and decades of study. It is probably not trapped wind or a cramping diaphragm, and a big meal beforehand makes it far more likely.
Weekly scans found thigh muscle grew measurably within about three to four weeks, once early swelling was discounted. A biopsy study found real fibre growth appeared only later, at ten weeks.
The endorphin story is a long-standing guess. When researchers blocked opioid signalling in 63 runners, the euphoria and calm still arrived — pointing to the body's own cannabis-like molecules instead.
For everyday exercise, food and water replace what sweat takes. The dangerous salt problem in endurance events is usually too much fluid, not too little sodium — and extra salt does not prevent it.
The familiar explanation — dehydration and lost salts — is the weakest part of the evidence. The better-supported idea is that cramping is a failure of nerve control, which is why a mouthful of pickle juice can stop one.
An umbrella review of 29 systematic reviews and 863 randomised trials found most treatments resting on critically low-quality evidence. Animal work suggests soreness can arise without muscle damage at all.
Trials measuring it are small but consistent: nasal breathing lowers peak oxygen uptake and feels harder at intensity. The interesting findings sit at submaximal effort, not maximal.