Reasons Why Elite Marathon Runners Are Skinny-Explained

If you've watched long-distance running competitions, you can't fail to notice that most runners are skinny, contrasting with those who run sprints and other short races. Do you ever wonder why are marathon runners skinny? 

In summary, runners are predisposed to be skinny because of their training routine that doesn't allow glycogen and fats to build once they deplete after using them as an energy source for hours of running.

But this doesn't give a complete overview of why runners are skinny. Here are the explained reasons to put your mind at ease.

Major Reasons of Why the Elite Marathon Runner Are Skinny Long regular workouts

The training regime of elite runners is brutal and often last more than 2-3 hours. These training habits are crafted to make them last longer on the road tapping on all energy reserves every time they practice. 

Distance runners can endure six days a week while averaging more than 2 hours of running. If you train this way daily, you will burn all fat reserves with no time for restoration between the next training session. 

Athletes use glycogen (natural body fuel culminating in carbs stored in the liver and muscles) within the first 90 minutes of running. After the glycogen is depleted and you still have to train, the body taps into using fats as fuel. 

Using large deposits of fats will eventually leave you looking lean because your body doesn't have any fats in the reserves. 

You can restore glycogen through nutrition (supplements and foods) within 24 hours. 

It takes the average runner 90 minutes to deplete all the glycogen from the body. If you are an elite runner, it will be even faster. Consistent training every 5-6 days a week means that your glycogen levels deplete, leaving you no excess carbs to convert into fats. 

The average runner can have the fat level drop below 15% for men and 20% for women. Research shows that the fat percentage of male athletes affects their performance and race results. 

You might get in the miles on your legs and pace to match, but the more skinny the person, the chances they will emerge victors. 

Lean Efficient Muscles

Athletes use two types of muscles. Slow twitch and fast twitch muscles depend on the distance they run. The difference between marathon runners and sprinters is the muscle fiber each uses.

Slow Twitch Muscle Fibers

These muscles become active when training for less intense activities like long-distance running. Running a marathon doesn't require intensity, but you should have endurance.

Fast Twitch Muscle Fibers

These muscles get active for short races when the athlete requires short energy bursts and power. They are explosive but lack endurance, so the athlete gets tired quickly.

Sprinters use fast twitch muscle fibers because they need to be explosive; these form because of how they train. The more fast twitch muscles you rely on, the bulkier an athlete gets. 

The training makes them develop more muscles and glutes than marathon runners, who have lean, efficient muscles. 

Major Reasons of Why the Elite Marathon Runner Are Skinny

Genetic Predisposition

Every professional athlete you see in a certain sport has genetics working in favor of their success. You can see marathon runners who can't gain weight regardless of diet and strength training, making their bodies ideal for running at elite marathon levels.

Individuals' genes determine their physique, which becomes an advantage towards a specific sport for the athlete. Elite runners chose the sport because they were already better than their peers. Their body constitution gives them a natural ability to endure long-distance running with little effort compared to their peers from a young age. 

For instance, Olympic swimmers have a genetic constitution that allows them to become fast swimmers. Their genetics include big feet, palms, and long arms. You can see that they have a wider upper body that gives them the advantage of strength and power over other people that lack similar genetic benefits.


Marathon runners need to have a lean shape; getting it is no walk in the park. While running forms the bulk of the exercise, it only constitutes more than half the work to get you into the best running shape.

Your diet constitutes your success in distance running and training. Marathon runners need to consume food rich in high carbs and proteins because they deplete the reserves often. 

To aid your recovery, you need foods that boost your metabolism to support your running routine. 

You can try these foods to maintain the lean shape you must have as a distance runner

● Whole grains

● Avocados

● Egg white

● Lean beef

● Frozen berries

● Nuts

Not All Runners are Skinny

What happens to people who want to run the marathon but don't want to become skinny?

I suggest the power of observation. Big city events like the Boston Marathon have over 95% finish rate. Not all runners that can finish a marathon are skinny except the elite runners who do it for a living. 

If you want to become a runner and not be skinny, you should have a training plan that supports calorie loss and allows fat to build from excess glycogen. Consume carbs after training and have more intake of foods rich in protein and fats in your diet to compensate for the calories you burn. 

You can also include strength training and weightlifting in your training schedule to help you build mass. Remember not to overdo the training, as this can set you off from your goals with injuries, pain, or soreness. 


Getting to know why are marathon runners skinny will help you understand how to train for the race distance that you want and maintain the right body shape. Marathon runners need lean, efficient muscles that can endure the distance. Their training program makes them lack fat reserves, making their bodies lean.

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