This is what running 26 miles actually does to your body

Metro

26-04-2025

This weekend thousands of people will be pounding the pavement in London, as the London marathon takes place.
The runners will be undertaking the 26.2 mile route, and whether they're an elite athlete or a novice, there's no denying that it will have a major impact on their bodies.
Even with all the necessary training and all the right gear, even the fittest of individuals will notice considerable changes to their body when running such a distance.
Obviously, it goes without saying that running a marathon is a very personal experience and a variety of things will affect your run – such as stress, injuries and training. But, on the whole, there are a few different things that will happen to your body during it, and afterwards.
From endorphin surges to back 'bounces', experts share some of the things to expect when you run 26 miles.
Pounding the pavement for 26.2 miles will have an impact on your body (Picture: Getty Images)
Body enters overdrive mode
When running a marathon, your body goes into overdrive, uses up energy stores, breaks down muscle, and loses fluid and electrolytes.
Physiotherapist Sammy Margo, who works with Deep Freeze and Deep Heat, explains: 'The body goes into overdrive, uses up glycogen (energy) stores in the liver, breaks down muscle and loses fluid and electrolytes – all of which contribute to fatigue and a sense of grogginess and tiredness after the run.'
Muscles become inflamed
Obviously, most people don't run 26 miles every day – so it's a bit of a shock to our muscles.
Sammy says: 'Muscles become inflamed and sore – particularly the calves and thighs – and runners may develop cramp.
'Biomarkers of muscle damage – such as lactate dehydrogenase and creatine kinase – increase during the run, peaking after the end of the marathon.
'These enzymes take around a week to fall back to normal levels.'
She says warming up is essential to reduce the risk of sore muscles, particularly delayed onset muscle soreness (DOMS).
Proper stretching and warm ups are essential (Picture: Getty Images)
Performance Physique's Head Coach, Arj Thiruchelvam, also adds that marathons cause substantial muscular damage – and this is even more noticeable if runners lack sufficient carbohydrate fuelling.
He says: 'Very often we consider the impacts are limited to the visual (blistering, nail issues or swollen feet) but many runners also suffer joint discomfort post-race to go along with their muscular soreness.
'These sensations are not the limit and that is why recovery is so vital.'
Cramps and joint discomfort are common
From over-contraction and overuse of muscles to a lack of sodium, there are numerous reasons why runners experience the notorious 'cramp'.
Kimiko Ninomiya, the founder of women's running collective Hot Boys Athletics, is running today – her sixth marathon – and she expects a few cramps and aches to happen.
She explains: 'This time around, I like to think I've properly prepared and I've been consistent about all my training (from everything I've tracked on Strava, you'd say I'm ready). But I'm prepared for the race to take everything out of me. I'm expecting my hamstring to cramp up, ankles and knees to ache, back pain, a headache – literally all the worst things I've ever experienced combined into one race.
'I'm expecting to hobble from the finish line, like Bambi, while simultaneously feeling a wave of euphoria wash over me for having just finished such a hard effort.
'In the days following a hard race, my legs are always very stiff but it's important to try to get moving, whether it's tracking a short and easy run on Strava or going for a long walk around the city (my favourite is to go to an art gallery).'
Feeling on top of the world – followed by post-run blues
Get ready for 'feel good' endorphins (Picture: Getty Images)
'Runner's high' is a real thing – and it's all down to endorphins.
Sammy continues: 'Running this distance over several hours also increases positive neurotransmitters, like norepinephrine, and 'feel good' endorphins – which keeps you alert and serotonin, which improves mood.'
But, in a similar way to a workout class, this effect does wear off shortly afterwards.
Kimiko says: 'Beyond the very physical toll, there's also the chemical drop-off that happens, when your serotonin levels switch off that my friends and I call 'marathon melancholy', where you feel quite sad/down, so it's important to give yourself grace and try to surround yourself with people or things that lift you up.'
You'll get (temporarily) shorter
According to the Journal of International Medical Research, you're expected to lose almost half an inch in height during a marathon.
This loss in height is a result of the back muscles tensing under strenuous conditions and fluid loss between the intervertebral disks.
But, worry not, this is only temporary and you'll be back to full height when fluid levels are replaced.
Stress on knees, hips and ankles
Even when you've trained, your body still goes through a tremendous amount of stress while running.
Physiotherapist Ben Lombard says: 'The muscles in your hips, knees, ankles and spine are constantly loaded with each step, which is a great way to strengthen them – but if loaded too much too soon you can easily create overload injuries.
'These commonly include muscle sprains, tendon injuries, or even ligament sprains and bone stress injuries.'
Ben says to help lessen the load on your joints, it all comes down to training and preparation.
He explains: 'To run 26.2 miles, you should condition your body appropriately with a carefully considered training plan.
'This should include both running and strength and conditioning sessions. Your runs should get progressively longer, and ideally you will do some shorter faster intervals, some race-paced runs, and some hills, too.'
Strain on your spine
While you might think your knees and ankles get the worst of it when running 26 miles, Michael Fatica – a consultant osteopath for The Back in Shape Program – says it's actually our backs that take the full impact.
He explains: 'The action of running causes a repetitive impact on the load bearing structures of the lower back – primarily the discs.
'When running, the main force is one of impact going through the body, the joints of the lower limbs, ankles, knees and hips and the into the spine. When we think of the impact on our lower back – even with good posture – the average marathon consists of somewhere between 55,000 and 65,000 steps.
'Think of these steps as tiny impacts through the spine for the duration of the event. From the outset in the early part of the race, you're likely soft on your feet, posture tall and efficient. As time wears on and the number of steps climbs, more and more of these impacts will become less efficiently handled by our bodies.
'At the same time, your postural muscles will be having to manage these many 'bounces' up and down during the entirety of the event.'
As a result, runners might experience fatigue and discomfort in the lower back at the end of the gruelling run.
This article was first published on September 25, 2023.
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