Why Marathon Runners Are Incredibly So Skinny

Why are marathon runner so skinny

Marathon running is like a symphony of strength, endurance, and sheer determination. But have you ever wondered why marathon runners seem to defy the laws of physics with their slim, trim physiques? It’s like they’re built for speed, with every ounce of excess weight shaved off to make them as efficient as possible. So why are marathon runners so skinny? Turn over the stones and find out.

Reasons Why Marathon Runners are so Skinny

Marathon runners possess a unique physique characterized by lean, toned muscles rather than bulky, hypertrophied ones. This streamlined physique is the result of various physiological and lifestyle factors inherent to marathon training and endurance running. Let’s dive into some reasons:

1. ​​Longer, More Frequent Training Sessions

If you’re contemplating the idea of running a marathon, it’s crucial to understand the significant commitment involved in training. Most marathon training plans span 12–20 weeks, requiring dedication for over 3–4 months or even longer.

Marathon runners typically adhere to a vigorous training schedule, often running 3-5 days per week and covering a total distance of 26.2 miles weekly through these sessions. It’s a substantial commitment, but one that’s entirely achievable.

Before you become overwhelmed by the numbers, it’s important to note that millions of individuals worldwide have successfully completed marathons. In 2022 alone, an estimated 11 million people crossed the finish line, demonstrating that with determination and commitment, you too can accomplish this feat.

Now that you’re reassured, let’s explore how the frequency and intensity of marathon training impact your muscle mass and fat levels.

Lean Muscle Magic with Marathon Running

Ever been stranded on the roadside because you ran out of gas? It’s happened to the best of us. But what if you had a backup tank? Pretty cool, right? No more being stuck! But here’s the catch: the more you use that backup tank, the smaller your car gets. Well, marathon running is a bit like that.

When you run for a long time at a steady pace, you tend to build leaner muscles instead of big, bulky ones. That’s because your body mainly uses a type of fuel called glycogen when you run. As you keep running, your glycogen stores run low. So, your body starts using fat as fuel instead. 

This helps keep you slim by burning up any extra fat. And because your body is mostly using fat for fuel, your muscles don’t get as big. Instead, they become lean and strong, giving you the endurance you need to finish a marathon.

2. Slow-Twitch vs. Fast-Twitch Muscle Fibers

Why Marathon runners are so skinny?

Yep, those names might sound a bit odd for muscle fibers, but they’re accurate. And you know what? They’re a big reason why marathon runners tend to have smaller muscles.

Slow-Twitch Muscle Fibers

These specialized fibers excel at providing sustained energy during endurance activities like long runs, half marathons, and marathons. They boast a high capacity for aerobic metabolism, making them the go-to choice for prolonged, moderate-intensity exercises

Through consistent marathon training, individuals like you develop a greater abundance of slow-twitch fibers in your legs compared to fast-twitch counterparts. This prevalence contributes to the development of leaner, more enduring muscles, essential for enduring the rigors of long-distance running.

Fast-Twitch Muscle Fibers

Fast-twitch fibers, on the other hand, are designed for quick bursts of power and strength. While you typically have fewer fast-twitch fibers, engaging in strength training exercises like leg presses can stimulate their growth. 

However, unlike slow-twitch fibers, fast-twitch fibers have a propensity to bulk up muscles due to their anaerobic nature. Consequently, marathon participants often exhibit a sleek, streamlined physique, emphasizing endurance over raw power.

Type of FiberContraction SpeedTime to Reach Maximum PowerFatigue Rate
Slow-Twitch (Type I)Slow100 Milli SecondsSlow
Fast-Twitch (Type IIA)Fast50 Milli SecondsFast
Fast-Twitch (Type IIB)Very Fast25 Milli SecondsFast

3. High Repetition, Low Resistance Training

Marathon training often incorporates high-repetition, low-resistance exercises to enhance endurance and muscular efficiency. Unlike strength training aimed at muscle hypertrophy, these workouts focus on improving muscular endurance and stamina. 

By repeatedly performing exercises like bodyweight squats, lunges, and core exercises, you build lean, toned muscles that are well-suited for prolonged periods of activity. 

This training regimen not only promotes cardiovascular fitness but also enhances muscular endurance, reducing the risk of fatigue and injury during long-distance running, even long distance walk. Consequently, you develop a lean and streamlined physique optimized for endurance performance.

4. Energy Efficiency 

When it comes to marathon running, energy efficiency is key, and it’s a big reason why marathoners tend to have smaller muscles.

Here’s how it works: When you’re running for such long stretches, your body has two options:

  1. Building Muscle Mass: One option is for your body to utilize the extra energy to bulk up your muscles. However, in the context of marathon running, this isn’t the most efficient use of energy. Packing on muscle mass requires significant resources and might slow you down during long-distance runs.
  2. Developing Endurance-Focused Muscles: Alternatively, your body can channel that energy into developing muscles that prioritize endurance over size. These muscles are finely tuned to sustain prolonged periods of activity, making them ideal for activities like marathon running. By focusing on building lean, efficient muscles, your body can optimize its performance and endurance over the course of a marathon.

At the heart of it all, it’s about survival. Man, it is amazing when you put it into perspective. Our bodies are wired to conserve energy and adapt to our surroundings. And that includes adapting to the demands of running marathons!

5. Oxygen Consumption

breathing plays an important role for the skinny physique of runners

Breathing plays a critical role, particularly during the arduous task of completing a marathon spanning over 26.2 miles. It significantly influences the physiological adaptations that occur in response to the demands of such a grueling endurance event.

Understanding the intricacies of muscle fibers sheds light on why marathon runners like you tend to possess a lean physique. Slow-twitch muscle fibers, which dominate the muscles of endurance athletes, are inherently leaner and demand less oxygen compared to their larger, bulkier counterparts. This inherent efficiency in oxygen utilization makes it advantageous for marathon runners to cultivate smaller, leaner muscles.

By having muscles optimized for endurance rather than size, you can maintain an efficient flow of oxygen throughout the entirety of the race. This sustainable oxygen flow is crucial for enduring the prolonged physical exertion demanded by a marathon.

In contrast, if marathoners were to rely on larger muscles that require more oxygen, they would likely experience premature fatigue, impeding their ability to sustain their pace and complete the marathon successfully.

6. Nutrition

Nutrition also plays an important role for marathon runner

When we talk about marathon running, nutrition becomes super important. You really need to make sure you’re eating right to keep up with the demands of long-distance running. Here’s why nutrition is so important:

Caloric Deficit

On average, marathon runners burn nearly 100 calories per mile during their runs. For elite distance runners, this translates to a significant calorie expenditure during training sessions. However, consuming enough calories to match this energy expenditure can be challenging.

Due to the high volume of calories burned during training, you often find yourself in a caloric deficit. This means you’re expending more calories than you’re consuming, which can contribute to the development of smaller muscles.

Read Next: Measure The Calories You Burned Running Each Mile

Healthy Eating

Now, let’s talk about what you eat. It is all about healthy and clean things. Think whole grains, lean proteins like chicken or fish, and plenty of fruits and veggies. These foods give you the energy you need to train hard and recover well.

Eating clean is a big part of getting ready for race day. By loading up on nutrient-rich foods, you can fuel your body for those long runs and stay in top shape. So, if you’re training for a marathon and aiming to shed some weight, sticking to a healthy diet is key.

7. Genetics

It’s all about your DNA, folks! Ever try one of those DNA tests that reveal your ancestry and genetic predispositions? They’re pretty fascinating, showing not just where you come from but also some of your genetic tendencies.

For instance, some DNA tests can tell you if you’re more likely to develop certain diseases or if your earlobes are attached or detached!

When it comes to why marathon runners tend to have smaller muscles, a big part of it boils down to genetics.

Destined to be a Runner

Professional athletes often possess genetic advantages that contribute to their success in sports. Many elite marathon runners like you are inherently gifted with a low body mass index (BMI) from birth, giving them a natural edge in long-distance running.

This genetic predisposition sets you up for triumph in marathon events, as your body is finely tuned for endurance and efficiency. Thus, a significant factor behind why you tend to have smaller muscles is rooted in your genetic makeup.

But, if this description doesn’t quite fit you, no worries! Running a marathon isn’t just for the genetic elite. It’s a journey that anyone can embark on, regardless of their genetic makeup. After all, the road to marathon success is paved with determination, grit, and a whole lot of heart.

Benefits of a lean physique for Marathon Running

There are many Benefits of a lean physique for Marathon Running

A lean physique offers several advantages for marathon runners, contributing to their success on the track and enabling them to perform at their best.

By prioritizing a lean physique through training and nutrition, marathon runners can optimize their performance and achieve their goals on the track.

Enhanced Endurance

A lean physique typically translates to a lower body fat percentage and an optimized muscle-to-fat ratio. This composition allows marathon runners to carry less excess weight, reducing the energy required to propel themselves forward. With lighter body mass, runners can sustain their pace for longer durations without experiencing premature fatigue, ultimately enhancing their endurance during the grueling 26.2-mile journey.

Improved Efficiency 

Marathon running is as much about conserving energy as it is about exerting it. A lean physique contributes to improved biomechanical efficiency, allowing runners to maintain a more economical stride and minimize energy expenditure per mile.

With less energy wasted on unnecessary movements or supporting excessive muscle mass, runners can channel their efforts more effectively, leading to better overall performance and faster race times.

Reduced Risk of Injury 

Carrying excess body weight, especially in the form of bulky muscles, can increase the strain on joints, tendons, and ligaments, predisposing runners to injuries such as stress fractures, tendonitis, and muscle strains.

Conversely, a lean physique places less stress on the musculoskeletal system, reducing the risk of overuse injuries and enhancing overall durability. By maintaining a lean and streamlined body, runners can minimize the likelihood of setbacks and stay on track with their training and racing goals.

Optimal Heat Dissipation

Endurance events like marathons often expose runners to challenging environmental conditions, including high temperatures and humidity. A lean physique facilitates more efficient heat dissipation through an enhanced surface area-to-volume ratio, allowing runners to regulate their body temperature more effectively during prolonged exertion.

How Can I Keep Gaining Muscle and Run at the Same Time?

Keeping cardio exercise in your routine offers numerous benefits, and there are clear steps you can take to ensure continued muscle gain while incorporating running. Consuming a diet with a caloric surplus is essential for supporting muscle growth while allowing running to remain a key component of your routine. 

Ensure you eat a balanced diet with an adequate amount of protein, as protein plays a crucial role in muscle building. Additionally, consider incorporating protein shakes or supplements to aid muscle growth and recovery.

Weightlifting, especially compound movements that work multiple muscle groups simultaneously, is crucial for building muscle alongside cardio. Focus on progressively lifting heavier weights with lower repetitions to promote muscle hypertrophy. Combining cardio with strength training creates the perfect synergy for achieving a healthy balance of muscle, fat, strength, and endurance.

Strength training activates fast-twitch muscle cells, enhancing aerobic capacity to support runs with strength and power, while running provides overall endurance and stamina to complement weightlifting sessions. This combined approach ensures optimal fitness and performance gains while allowing you to enjoy the benefits of both cardio and strength training.

Benefits of Adding Running to Your Workout Routine

1. Weight Management

Running serves as a dynamic tool for weight management within your workout regimen. By integrating running sessions into your routine, you engage in a high-calorie-burning activity that facilitates weight loss while preserving lean muscle mass. This balanced approach ensures that as you shed excess pounds, you maintain a toned and sculpted physique.

2. Cardiovascular Health Boost

Incorporating running into your workout routine provides a powerful boost to your cardiovascular health. This aerobic activity elevates your heart rate, strengthens the heart muscle, and enhances blood circulation throughout the body. By regularly challenging your cardiovascular system through running, you reduce the risk of heart disease, stroke, and other cardiovascular conditions.

3. Stress Reduction and Mental Well-being

Running offers a therapeutic outlet for stress reduction and promotes overall mental well-being. The rhythmic motion of running, coupled with the release of endorphins, produces a natural mood lift and reduces feelings of anxiety and depression. By incorporating running into your workout routine, you cultivate a sense of calmness, clarity, and emotional resilience.

4. Endurance Enhancement

Engaging in regular running sessions as part of your workout routine leads to significant improvements in endurance and stamina. As you gradually increase your running distance and intensity, you enhance your body’s ability to sustain prolonged physical activity without fatigue. This heightened endurance not only benefits your running performance but also translates into greater vitality and efficiency in everyday tasks.

5. Social Connection and Community Engagement

Running fosters social connection and community engagement, enriching your workout experience beyond the physical benefits. Whether participating in group runs, joining running clubs, or attending local races, running provides opportunities to connect with like-minded individuals and build meaningful relationships. The supportive network of the running community offers encouragement, motivation, and a sense of belonging.

6. Cognitive Function Enhancement

Running positively impacts cognitive function, sharpening memory, focus, and mental clarity. The increased blood flow and oxygen delivery to the brain during running stimulate neural growth and synaptic connectivity, enhancing cognitive performance.

Why are Sprinters so Muscular and Long-Distance Runners so Skinny?

The distinct physiques of sprinters and long-distance runners stem from the diverse training and physiological demands of their respective disciplines.



Sprinters are known for their powerful and muscular physiques. This muscularity is a direct result of their training, which emphasizes short, intense bursts of speed.

Sprinting primarily engages fast-twitch muscle fibers, which are optimized for explosive power. The rigorous workouts, including short sprints and weight training, encourage muscle growth and contribute to a bulkier appearance.

Long-Distance Runners

Conversely, long-distance runners, particularly those training for marathons, prioritize lean and slender physiques. Their training involves extended, low-intensity runs that activate slow-twitch muscle fibers, ideal for endurance.

This emphasis on endurance over raw power leads to leaner muscles that can sustain prolonged, low-intensity efforts. Long-distance runners also focus on conserving energy, often shedding non-essential muscle mass, particularly in the upper body, to improve efficiency.

So, when comparing sprinters and long-distance runners, their diverse training goals and muscle fiber engagement explain the striking contrast in their physical appearances.

Sprinters prioritize muscle power, resulting in a more muscular build, while long-distance runners prioritize endurance, leading to a slender and lean physique. Both are remarkable athletes, but their training objectives sculpt their bodies differently.

AspectSprintersLong-Distance Runners
Training EmphasisShort, intense bursts of speedExtended, low-intensity endurance runs
Muscle Fiber EngagementFast-twitch muscle fibersSlow-twitch muscle fibers
PhysiqueMuscular and powerfulLean and slender
WorkoutsShort sprints, weight trainingLong runs, lower intensity
Muscle GrowthEmphasis on building muscle massLeaner muscle composition
Energy EfficiencyFocus on short, explosive effortsPrioritization of energy conservation
Upper Body Muscle MassOften developed and maintainedMay shed non-essential upper body muscles
IdealShort-distance sprints and powerLong-distance endurance and stamina
Training ObjectivesExplosive speed and accelerationProlonged endurance and efficiency

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