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marathon running, muscle cramps, electrolytes

What happens in the body during a marathon run?

Written by: Anu Munkhtur



Time to read 5 min

Keywords: marathon running, muscle cramps, electrolytes

What happens in the body during a marathon run? How does your diet influence your performance, and how can you deal with cramps and the painful stomach pain when running a marathon?

Let us see what our body undergoes as we run a marathon and how we can successfully prepare ourselves for it in advance, so that when the time comes, we are ready to go. 

marathon running, muscle cramps, electrolytes

1. Understanding the Role of Electrolytes in Marathon Running

In the context of marathon running,  electrolytes play a pivotal role in maintaining bodily functions and ensuring peak performance.

As you run, your body loses fluids and electrolytes through sweat , leading to a decrease in aerobic performance and potential health risks if not adequately replaced.

The most common electrolytes lost are  sodium, potassium, chloride, and calcium , all of which are vital for muscle function and maintaining fluid balance.

When these electrolyte levels drop too low, it can lead to symptoms such as muscle cramps , fatigue , and even hyponatraemia (a condition characterised by low sodium levels in the blood).

To counteract these effects, many marathon runners rely on electrolyte replacement drinks or supplements.

These products are designed to quickly replenish lost electrolytes and provide hydration, helping to maintain endurance and prevent muscle cramps.

Proper electrolyte balance aids in post-marathon recovery by assisting in  tissue repair

marathon running, muscle cramps, electrolytes

1.1. Hitting “The Wall”

Hitting the wall  is a dreaded experience for marathon runners, where they experience a sudden and dramatic drop in energy levels.

This often occurs around the 20-mile mark , but can vary depending on individual training and fueling strategies.

It's essentially your body crying out for fuel. As many as 28% of male runners i n a study by NIH hit “the wall” in comparison to just 17% of female runners.

You've depleted your readily available glycogen stores (carbohydrates) that power your muscles, and without proper training your body may struggle to switch to using fat for energy.

This translates to feelings of fatigue, muscle weakness, and a significant drop in performance – all signs that you need to adjust your race plan and refuel strategically to get yourself back across the finish line.

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2. Runner's Gut and Muscle Cramps

Gut pain and muscle cramps are common issues that can deter beginners from continuing their marathon training.

The phenomenon known as 'Runner's Gut ' arises due to a redirection of blood from the gut to working muscles during exercise, causing discomfort.

High fibre, fat, and protein meals consumed right before exercise can exacerbate this discomfort  and arise as a result from the Runner’s Gut post exercise. Other issues such as diarrhoea  and digestive issues may also arise post exercise.

Consulting with an experienced sports dietitian can help identify triggers and devise strategies to avoid them.

Two theories exist about muscle cramps, and namely:

1. During running they are caused by mineral deficiencies or dehydration.

2. They occur due to over-contraction or overuse of muscles, or lack of muscle strength.

Over-training in the days leading up to an event can increase the risk of cramps.

To prevent cramps, it's recommended to train sufficiently for the race distance, build leg muscle strength, pace the race carefully, and taper training in the days leading up to the race.

marathon running, muscle cramps, electrolytes

3. Breathing and Oxygen Economy in Marathon Running

As you embark on a marathon run, your body undergoes a significant shift in cardiovascular activity.

Initially, during a speed run, your body operates in an  anaerobic state , relying on stored energy sources.

However, as you transition into an endurance run, your body switches to an increased oxygen intake to fuel the muscles.

This is where the concept of ' running economy ' comes into play.

Running economy refers to the amount of oxygen consumed while running at a certain pace.

A better running economy means you use less oxygen at a given pace, which is crucial for long-distance runs like marathons.

Factors such as strength training and increased training volume can improve your running economy.

Furthermore, efficient breathing techniques, like rhythmic or diaphragmatic breathing , can enhance oxygen intake, thereby improving your running economy and overall marathon performance. 

4. Diet in Marathon Performance

As you approach a marathon, your diet plays a pivotal role in your performance.

During the run, your body significantly depletes its glycogen stores , exhausting a substantial number of calories that need to be replenished.

A carb-rich diet is particularly beneficial for marathon runners, as carbohydrates are the primary source of energy for your muscles.

According to the International Society of Sports Nutrition (ISSN), athletes following intense training schedules need to consume between 5–12  grams per kg of carbohydrates per day.

This high carbohydrate intake helps maintain glycogen stores, ensuring sustained energy levels during the marathon.

Consuming carbohydrates during and after the run also aids in replenishing glycogen stores and facilitating muscle recovery.

  • Right after exercise: Drink a carbohydrate supplement to jumpstart the process of rebuilding your muscle glycogen (the energy your muscles store).
  • Keep it going: Continue consuming carbs at regular intervals to maintain the process. Aim for roughly 1.2 grams of carbs per kilogram of your body weight per hour.

While it's essential to meet calorie needs, the  NIH  recommends keeping fat at around 30% of total calories.

marathon running, muscle cramps, electrolytes

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