Running has long been a popular sport due to its accessibility and cardiovascular benefits. The styles of running are as varied and diverse as the individuals who take part in the sport; from sprinting to marathoning to even a light jog at the park after work, running is a sport in which almost anyone can partake in.

But what impact can running as an exercise have on body composition? Furthermore, what impact does body composition have on the act of running?

Whether you’re the seasoned runner looking to increase your pace and decrease your race time or the casual weekend runner, knowing the science of how running interacts with body composition can be beneficial in helping you accomplish your goals.

How Body Composition Impacts Running

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 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. A separate study took the same approach of evaluating this relationship between body composition and running performance in recreational marathon runners. 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, lowering your body fat percentage can help you achieve your best run time, though your body fat goals should be based on the type of running you do.


There’s a preconceived notion in society about what a runner’s body should look like, when in fact, runners come in different shapes and sizes. If you’re concerned that your current body composition will limit you from becoming a successful runner, just relax; it’s time to let that idea go.

Body fat mass 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 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 looking to optimize their body composition.

The Effects of Running on Body Composition

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


An in-depth analysis into the effects of running and body composition was conducted on ultramarathoners 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 effects throughout the duration of the race.

The participants lost 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 not adversely affect muscle mass.

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 muscle loss? In cases of long duration training, overtraining 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.


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: fat free mass was maintained but body fat mass was reduced by an average of 11 pounds. 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 style running.

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

Now the question remains, which one should you do?

Endurance Running vs. Sprinting

You often see banter back and forth between long-distance runners (half marathoners and marathoners) and short-distance runners (sprinters and 5K runners) about which type of running is a better use of time. 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 effects 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!

Body composition has a direct relationship with running, both on the effects of the sport itself and as a result of partaking. Running has been proven as an effective fat loss method with minimal muscle loss when participants are properly nourished and allow their body ample rest and recovery.

Trained runners looking to further improve performance may not always benefit from more running; cross training with resistance exercises and diet management can help shave time off your personal best. But even if you’re new to running, you can improve not only your overall health but also your body composition by adding some running to your routine.

If you’re new to running, start with small, achievable goals. It’s tempting to go out and run as fast as you can for as long as you can, but you’ll last longer and grow stronger if you start with small steps. Add a couple of minutes of running to your walks and gradually increase the time spent running. Begin slow, be patient with yourself, and don’t worry about your how fast you’re running yet.  Even small steps can have a profound effect on your body composition, and you’ll be running longer and faster in no time. With a consistent running program, start tracking those body composition changes and watch how much you can achieve.

By Nikita Ross Contributing Author to

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