What Does A Half Marathon Do To The Body?

The half-marathon is only 13.1 miles but needs excessive training to get your body accustomed to the stress and endurance that awaits. Running a half marathon is not only physically exhausting but also a mental challenge.

Running is fun and healthy, but it does have a massive impact on your body.

While running a half marathon, your brain, muscles, and organs work extremely hard to cover the 13-mile distance. Your heart and breathing will increase in rhythm to ensure oxygen and blood flow delivery throughout the body. In addition, the working body will result in muscle fatigue and water loss.

So, you’ve trained well, prepared your body with a good diet, and your running gear is top-notch. These are all essential requirements before attempting the 13-mile race.

But what does a half marathon do to the body?

What Happens To Your Body In A Half Marathon?

what does a half marathon do to the body

As a runner, you experience the aches and pains firsthand, but have you ever thought about what your body has to endure to carry you across the finish line?

Let’s take a look!

Muscle Fatigue

Muscle pains are the most common effect of running as your muscles fatigue and fiber damage occurs.

However, the results can also relate to shin splints, calve muscle pain, and micro tears to hamstrings and quads. Luckily, muscle fatigue can be treated with light stretching and taking in plenty of fluids to replace electrolytes. 

On the half marathon day, you will put in a lot more effort and pace than on training days; so you will also experience more muscle pain and soreness during and after the race.

With the extra strain, lactic acid will build up in your muscles, and small muscle tears can occur.

Delayed Onset Muscle Soreness (DOMS) can result from extreme fatigue and can take a few days to repair.

While you should expect a recovery period of 2-3 days (more if it is your first half marathon), muscles will repair significantly faster than what you’d expect after a full marathon.


Dehydration is not so common in half marathons as runners typically take in enough fluids to replace water loss and glycogen.

However, high humidity or temperatures may cause dehydration or other heat injuries. As with all activities, your body works extremely hard and uses a lot of energy and fluids; therefore, it requires replacement during and after the race.

Should you fuel during a half marathon? It normally depends on your expected finish time.

Heart Health

Running half marathons puts a lot of stress on your heart, lungs, and vascular system. Before running longer distances, you must gradually build up your fitness and endurance levels. Your heart is just a muscle and will become more robust with a slower rhythm and increased cardiorespiratory strength and endurance. 

While running, your heart is the main organ to ensure your muscles get enough blood flow and oxygen to perform the task. As a result, heart rates can shoot through the roof for the entire duration of the run.

Burning Calories

Your body will use every bit of food and energy stored to enable the continuous work rate that a half marathon requires. The average half marathon runner burns around 1500 calories during the two-hour running session.

So make sure to refuel again with lots of protein and carbohydrates after the run.

Musculoskeletal Injuries

Running has a lot of benefits, but unfortunately, the wear and tear on joints and muscles is a common downside of clocking in so many running miles. 

A poor technique multiplied by 21.1KM of hard running is a recipe for injury.


Cramping is very common during half marathon races, particularly in hot weather. Although many runners do not cramp, others do, and it may be a reflex between your spinal cord and the cramping muscle.

Like muscle spasms, the overworking muscles and the lack of quick blood and oxygen replacement can result in uncomfortable and sometimes painful cramping.

Sore Feet

The many miles of training and running a half marathon will put a lot of strain on your feet.

Plantar fasciitis is common. If you haven’t experienced it before after a half marathon – count yourself lucky!

In addition, the non-stop pounding of your feet on the surface may hurt the blood vessels and reduce red blood cell levels. Ensure to keep your iron levels up before and after races.

Plantar Fasciitis

Losing Weight

Losing water weight is part of the dehydration process while running a half marathon. Your body needs to cool while working continuously and cope with possible humidity and environmental temperatures.

Sweating is the leading cause of losing body fluids, and replacing it during the race and slowly afterward is imperative.

Feeling More Brainy

One of the positives of running as a sport is the overall fitness that results in a healthy lifestyle. A healthy body hosts a healthy mind comes to play when running a half marathon as the levels of serotonin and endorphins increase to put runners in an alert, calm, and a good mood.

Studies have also shown runners to be more cognitive, not only while running but overall.

Sore Nipples

Sore nipples are more common in male half marathon runners and are typically the cause of salty sweat, creating an abrasive layer on your nipples. In addition, the friction from your running gear on the nipples will cause them to become sore and sometimes even bleed.

Consider vaseline or nipple tape.

Immune System Temporarily Drops

Training extensively and then putting in the extra effort on a race day will drain your body from every resource it has and can lead to a suppressed immune system. It is more acute when you already feel unwell and contracted contagions before half marathon day.

Rest and replace your body’s fuel as soon as possible.

Toenail Injuries

Toenails being sore and even going black during half marathon races can be highly disruptive. The wrong shoes are the main reason for this injury. When the toenails continuously rub against the shoe, the blood vessels under the nail will break, resulting in sore and black toenails.

Short-Term Kidney Damage

Research shows that some marathon runners can suffer from AKI, Acute Kidney Injury when their kidneys cannot cope with the pressure of filtering the blood and equalizing fluids and electrolytes.

However, AKI resolves typically within a day or two when athletes effectively rehydrate and the kidney functions return to normal. 

The Physical Effects of a Half Marathon

Without training, running a half marathon will be detrimental to your body.

Even with the proper training and preparations, your body will still take a lot of strain and stress but will be able to cope and recuperate more quickly.

This is because all organs and muscles, including the heart, work extremely hard to ensure the body has constant blood and oxygen to function and endure until the finish line. 

Want to dive in and get started?

Check out our guide to running a sub-2- hour half marathon.

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Alex Randall

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Alex is the editor at Revel Sports. It was his idea to take our post-club-run chats and build a website out of them. He is responsible for dotting the I’s and crossing the T’s when any of us have something to post. (Basically: it’s all his fault). A ferocious 5K powerhouse on his day, Alex is known for not understanding the meaning of the term ‘negative split‘.
Alex Randall

Revel SPorts Contributor

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