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Editor’s Note: This post was updated on November 15, 2018for accuracy and comprehensiveness. It was originally published on April 19, 2017.

Running has long been a popular type of exercise due to its accessibility and cardiovascular benefits. The different types of options are as varied and diverse as the individuals who take part; from sprinting and marathon running to a low-intensity jog at the park after work, running is a cardio exercise with a distance and tempo that’s right for everyone.

Running is often a popular exercise for weight loss. If you are an avid reader of this blog, then you probably have more well-defined goals than losing weight. You understand that weight is just a number, and you are more curious about the components that make up your weight. Instead of a vague goal like “how much weight I can lose by running” or “Can running help me achieve my goal weight”, you probably have questions like:

  • What impact does body composition have on your running performance?
  • What impact can running as your primary form of exercise have on body composition?
  • If I experience weight loss by running, do I lose both fat and muscle?

Whether you’re the seasoned runner looking to decrease your mile time or the casual weekend runner who just wants to get in some cardio, understanding the science of how running interacts with body composition can be beneficial in helping you accomplish your goals.

How Body Composition Impacts Running

running on a bridge in the morning

First, let’s take a look at how your body composition impacts your speed and race time. Many runners have the goal of increasing their speed and perhaps setting a new personal best in an upcoming race. A recent study sought to find this link by evaluating whether body composition had an affect on race time in half marathoners, marathoners, and ultra-marathoners.

The researchers approached the study with the theory that skeletal muscle mass would have the largest impact on race times. On the contrary, the results showed that the amount of muscle mass was not related to training characteristics. The results actually showed that body fat percentage had the most significant impact on race results. This study indicated that having more skeletal muscle mass did not provide a clear performance advantage, but the varying body fat percentages in conjunction with training programs were directly related to both volume capability, endurance, and speed during training in all classes of marathoners.

These findings don’t only hold true in marathon runners— even short-distance runners’ performances are affected by body fat percentage. A separate study took the same approach of evaluating this relationship between body composition and running performance in recreational marathon participants. This study, however, aimed to explore the factors contributing to fast or personal best marathon race times in recreational male marathoners. The study showed that a low body fat percentage and high-intensity speed training are the two most prevalent factors in predicting race completion times.

In summation, decreasing your body fat percentage can help you achieve your best run time, though how much fat loss you should target should be based on the type of running you do.

Will Your Current Body Composition Prevent You from Running?

Some people falsely believe that in order to start running, they need to focus on losing weight in order to get into good enough shape to enjoy the benefits. Body fat percentage does not have a direct relationship with peak oxygen uptake levels, meaning your muscles still have the energy to get you going. This also means that having a few extra pounds more than another individual does not necessarily mean you shouldn’t run or even be hindered aerobically.    

Your speed may vary from fellow runners, and it will take time and training to increase your comfort or the distance you can run, but running is indeed a viable fitness option for individuals at any weight looking to reap the health benefits and optimize their body composition.

The Effects of Running on Body Composition

how running can benefit you

We now know how a runner’s body composition can affect run time, but how does running affect your body composition? Will running result in muscle loss? Do you have to run 5 miles a day to see improvement in fat loss? Let’s take a look.

Does running cause muscle loss?

An in-depth analysis into the effects of running and body composition was conducted on ultra-marathoners participating in the transcontinental Transeurope Footrace. The participants ran 2,787 miles over a period of several weeks. Throughout the course of this race, body composition was measured in relation to distance traveled to show the progressive changes throughout the duration of the race.

The participants experienced significant fat loss, losing approximately 40% of their body fat mass, while losing only 1.2% total lean tissue overall, the majority of which came from the runner’s legs. The researchers surmise that this loss was directly related to extreme caloric deficits and lack of recovery time provided to the exhausted leg muscles. So even in cases of extreme running distances, running alone did cause you to lose muscle.

In less extreme cases, running has been shown to have a positive effect on muscle mass. These findings indicate that running can be an effective way to gain muscle in untrained populations in addition to combating aging-related muscle loss.

So does running cause you to lose muscle mass? In cases of long duration training, over-training and improper fueling, sure. For the average runner who takes the necessary steps to protect their muscles? Not necessarily. Setting a proper diet plan will mitigate any concerns on this front.

Does running burn fat? At what intensity do I need to run to burn fat?

For those hoping to achieve their weight loss goals and lose fat, running is often heavily featured in any training plan for its calorie-burning benefits ( either as a warm-up, post-workout cooldown, or the workout itself).  

A recent evaluation was conducted on the effect of a 12-week running program on body composition in a group of young males. This recreational-style program resulted in a significant improvement in body composition in just a few months: fat-free mass was maintained but study participants averaged 11 pounds of fat loss. The same study also investigated the impacts of a 12-week soccer program, which yielded similar results to the running program. In regards to body composition, this investigation indicated that continuous running on a recreational scale may have similar effects with soccer, which requires more short-burst high, intensity style running.

So whether you’re running for long periods of time or for short sprints, your body composition will improve as you improve your body fat percentage.

Now the question remains, which one should you do?

Endurance Running vs. Sprinting

You often see back and forth banter between long-distance runners (half marathoners and marathoners) and short-distance runners (sprinters and 5K runners) about which type of running has better health benefits when it comes to changing your body composition. Sprinters will claim that sprint workouts will boost your metabolism and provide an afterburn effect. Distance runners say that their longer distances will burn more calories and create a greater calorie deficit. While there are a variety of different factors impacting each group, let’s focus on the effect of endurance running and sprinting on body composition.

A study evaluating both male and female endurance and short-distance runners took an overall look at the effect of a continuous endurance running program and a separate high intensity running program over the period of 12 weeks. Both groups had to participate in a half-marathon at the completion of the trial.

There was no significant difference in performance between the two groups during the half-marathon, and both groups saw a decrease in visceral fat content at the end of the 12 weeks. This study shows that in recreational running, both high-intensity and endurance training have positive changes on body composition in regards to fat loss.

So, if you’re trying to decide between long-distance or short-distance, both will help create positive change in your body composition and overall health. Choose the method that appeals to you the most and watch the positive changes come.

Time to Run With it!

running on the street for a marathon

The science is clear that running improves your body composition, which in turn improves your performance. Running has been proven as an effective way to lose fat with minimal muscle loss when participants are properly nourished and allow their body ample rest and recovery.

Trained runners looking to decrease their race time may not always benefit from more volume; cross-training with resistance exercises and diet management (both nutrition and getting enough calories) can help shave time off your personal best. But even if you’re a beginner, you can improve not only your overall health but also your body composition by adding running to your cardio routine.

If you’re just getting started, set small, achievable goals. It’s tempting to go out and start marathon running, but you’ll last longer and improve your cardio faster if you start with small steps. Add a couple of minutes of running to your walks and gradually increase the time. Begin slow, be patient with yourself, and don’t worry about your how fast you’re running yet.  Even small steps can have profound changes on your body composition and cardiovascular health, and you’ll be running longer and faster in no time.


Nikita Ross is a Precision Nutrition certified wellness coach and professional fitness writer. She believes that lifting both barbells and books is the key to self-improvement.

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