11 things that happen to your body when you run a marathon

As the final countdown begins before around 40,000 runners pound the pavements from Greenwich to the Mall in the London Marathon 2018, we take a look at exactly what happens to your body when you run a marathon.

Any marathon is a physical challenge like no other, but it’s impact on your body is actually far more than losing a toenail:

1. Your nose might run more

A study in the Journal Annals of Allergy, Asthma and Immunology found that 56% of runners get a runny nose while running for long periods. Why? It’s a common complaint and is often called exercised-induced rhinitis, or runners hay fever. As you breathe more, your nose kicks into hyperactivity, and the mucous membranes within the nose produce mucous, often accompanied by a watery discharge. Lovely.  

2. You’ll get temporarily shorter

Yes, it’s true, you’re expected to lose almost half an inch in height during a marathon. According to the Journal of International Medical Research, this loss in height is a result of the back muscles tensing under strenuous conditions and fluid loses between the intervertebral disks. Don’t fear, this is only temporary, your height will be fully restored when fluid levels are replaced.  

3. You might get cramp

Cramp is one of the most common complaints when running a marathon. Although nobody is really sure why some runners get cramp and others don’t, it’s thought to be a neuromuscular issue, caused by a malfunction in a reflex between your muscle and spinal cord. On race-day, cramp is often caused by setting off too fast, so stop and stretch it out as soon as you can unless you want to wave goodbye to your PB.

Related: How to deal with cramp when running a marathon

5. You might feel nauseous

You’ve just run 26.2 miles and are ready to reward yourself with all the free food and drink your medal allows, yet you suddenly feel sick even thinking about a burger. A 2008 study in the American Journal of Physiology found that a 60-minute session on the treadmill increased the amount of the gut hormone peptide YY, an appetite suppressant, and suppressed acylated ghrelin, an appetite stimulant.

6. Your toenails might go black…

There’s three different reasons your toenail might go black – a shoe that's too small, a toenail that comes into contact with the roof of the shoe too often, or a runner who uses their toes to grip too hard as the run. However it happens, the result is the same - blood vessels under the nail will break open, which spill blood (which looks black under the opaque nail) into the area between the toe bed and the toenail. Nice.

Related: How to look after your feet after running a race  

7. …or fall off entirely

Whilst we’re on the subject of toenails, once the skin beneath the black toenail begins to heal, the nail will die and fall off. Don’t worry, it’ll grow back someday.  

8. Your sore feet will tell you something  

Yes, they’ve coped with months of training, but the continual hammering of tiny blood vessels in the feet during the marathon can mean a drop in red blood cell levels. Rest after the marathon and ensure you get plenty of iron-rich foods, like meat, tofu and green vegetables.

9. You’ll lose 2-5kg of water weight

Most people will cross the finish line lighter than they started, but this is down to a loss in water weight. You should aim to replace this slowly, consuming 500ml of water per hour until your urine returns to a pale straw colour.

Related: How to stay hydrated during a long run or race 

10. You’ll feel like a genius

Running increases levels of positive neurotransmitters, like endorphins; norepinephrine, which is responsible for alertness; and serotonin, which helps regulate mood. Plus, running puts the brain in an ‘alpha-wave’ state, which is associated with feelings of calmness and wellbeing. As well as this, researchers at the University of Illinois found that 30-minutes of exercise resulted in up to a 10% improvement of cognition or being more effective in processing a problem or situation.

11. You’ll struggle with stairs the next day

Whether you’re a 2:30 or a 5:30 marathoner, your race-day pace tends to be faster than training days. This is the difference between pleasantly and painfully sore, as you accumulate lactic acid in your muscles as you increase the pace, which brings on premature fatigue. Plus, those extra miles on the day cause micro tears in muscles which probably haven’t totally healed from your training. Except stairs to be tricky on Monday.

12. Your nipples might bleed

A common problem for male runners, bleeding nipples are caused by sweat, which is a mix of water, salt and other minerals. When the water evaporates, you’re left with abrasive salt on your nipples, which can then chafe as you run, causing them to bleed. If you haven’t bought any nipple guards yet, it’s worth ordering some asap.