We’re all aware of the health benefits of exercise and the dangers of inactivity. But, exactly what does running do for your body?

Both Alex and I consider ourselves runners. Alex has run several marathons, including the Great Wall Marathon in Beijing and I have always been a big fan of 5Ks.

In December 2021, I ran the Honolulu marathon. It was my first marathon. When I began training and ramping up my distance, I was shocked by the changes I experienced, both physically and mentally.

In this article, we talk about how running affects your body composition, sleep quality, mind, and more.

What Does Running Do For Your Body Ryan and Alex Duo Life

what does running do for your body

Earlier this week, Alex’s 65-year-old father signed up for yet another marathon. He already has dozens under his belt.

If you can’t imagine yourself running marathons as you push towards 70 (and beyond!) ask yourself, “…why not?”

We’ve all heard the benefits of running and exercise — longevity included. As they say, you don’t stop running because you get old, you get old because you stop running.

But what does running do for your body, really? The answers will surprise you. And, no, your future doesn’t have to be riddled with injury (and we’ll tell you why).

As two marathon runners who have vastly different body types (even aside from the fact that Ryan is a man and Alex is a woman), we share much of the same unexpected benefits of running.

Both physically and mentally, running will change you.

And it’s for this reason — as well as how simple it is to get started — why we love running.

Running, as simple as it is, isn’t a one-size-fits-all activity. Some people view it as a punishment — who else’s high school soccer coach made them run sprints?! — while some view it as an existential and spiritual activity.

Some run to lose weight or tone up while others simply love the excuse of being outside. But whatever the reason for why you run, a lot is going on under the surface.

In this article, we talk about how running changes your body composition, sleep quality, mind, and more.

Here are the strange but true things that happen to your body when you start running — and how we’ve experienced them personally.

what does running do for your body physically

When you start running, these are the physical changes you can expect. Since most forms of exercise bring positive physical change, we’ll focus on changes from running or jogging specifically. 

The best news is that your pace doesn’t really matter. If you are sprinting, striding, running, or jogging, you still reap the benefits. 

Each of these points comes from our research of the science behind running and are corroborated by our personal experience. They are listed in order of most surprising (for us) to most obvious (but still very exciting)!

Lastly, a lot of people wonder about how running will change their physique. We’ll talk about general changes, but we won’t discuss specific topics like the ones below.

  • What does running do to your legs?
  • How will running change my body shape?
  • Does running tone your stomach?
  • Does running make your butt bigger?

While these are all valid questions, there is no correct answer for you on the internet. Sorry. Since every runner is so different, you should just run for three or more months and find out for yourself!

1. Knees and Back Become Stronger, Not Weaker

We all know someone who blames their wrecked knees or back on years of running and pounding the pavement. But… they may be misguided.

It turns out that the stress and impact from running make your body more robust — not weaker or more injury-prone. As someone whose 65-year-old father-in-law still runs marathons to this day, I can attest to this fact.

This may be controversial or at least counterintuitive, but hear us out.

More and more studies are backing this up and finding that running isn’t bad for the knees. Studies that followed groups of runners vs. non-runners actually found that the cartilage in the knee joint was healthier in runners after the age of 40.

As long as the runner wasn’t overweight or already suffering from significant knee injuries, there was no evidence that the risk of knee arthritis increased for runners.

Science is also suggesting that the same is true for spinal discs. One study has shown that running can strengthen spinal discs and reduce back pain. I can say with 100% certainty that this was the case for my back.

Running, especially when paired with strength and mobility training, will make your body tougher and more prepared for activities like hiking, skiing, or playing a game of soccer.

In my experience, running significantly reduces my lower back and neck pain. For me, this is easy to track since I have suffered from morning back pain for most of my adult life. 

Additionally, while this is controversial and not scientifically proven, we prefer running in minimalist shoes. Both for the improved experience, and the lower rate of injury in our experience. We love the Vibram toe shoes, however, any minimalist shoe that’s comfortable will do.

2. Sleep Quality Improves (Drastically)

Physical activity improves sleep. This is one of my favorite benefits of exercise.

Before I started running, I already worked out quite a bit. Could running improve my sleep even further? Well, the data is in. 

I took an average of my sleep data (via the Pillow App) from 3 months before and after I started running. Before, I was following workouts on Beachbody On Demand five days a week. After, I was training for my marathon 5 days a week. 

The results: my average sleep quality increased from 79% to 88% from when I started running.

That’s an 11% improvement! This is pretty amazing given that I simply transitioned from exercising at my home gym to running outside.

Additionally, as shown in the pie chart below, my REM sleep and deep sleep increased while light sleep decreased with running. All the data points to significantly better sleep. 

As I mentioned above, all of my running workouts were outside. The fresh air and Vitamin D surely played a part too. So get off the treadmill and get outside whenever possible. Your sleep will thank you for it!

what does running do for your body sleep improvement data

3. Running Can TORCH Calories

Coming from me, this means a lot. I have collected heart rate and calorie burn data on thousands of workouts. Partly because I am a geek, but mostly because I don’t love working out unless I can get the most bang for my buck. 

Years ago, Alex and I conducted an experiment to compare several types of cardio.

As graphed below, we compared running an 8.5-minute mile on a treadmill to doing the hardest HIIT workout we could find (Insanity Max: 30 by Shaun T.) Back then, I was really surprised how well running did up against this insanely tough workout. 

The results are impressive, especially given this was all done on a treadmill at a 0% incline. In real life, I run outside all over the mountains and even faster at 7 minutes per mile.

As you can see in the graph, Ryan’s treadmill calorie burn is lower than the Insanity workout, both during the “burn” (20-minutes of intense exercise) and the “afterburn” (60-minutes of inactive recovery). However, Alex’s calorie numbers were very similar for both workouts. 

For the full results of our cardio experiment, here is the full report.

what does running do for your body calorie burn and weight loss

By the way, when paired with eating the right amount of healthy foods, this means that running will help you lose weight or maintain a healthy weight. To get the most out of running, do it outside in the fresh air, find some hills, and vary your pace.

Running outside is much better and harder than running on a treadmill. No, running on a treadmill is not bad for you, it’s still good for weight loss. However, running outside is more effective (and enjoyable). 

To track your calories from exercise, get a fitness tracking watch, and to track your calories from food, follow the instructions in our 30-Day Weight Loss Challenge.

4. Running Will Find Your Weaknesses

I work out at my home gym for maybe 45 minutes a day… and it might take me weeks before noticing an imbalance or injury. During one 45-minute run, I’ll probably identify several concerning twinges.

Your body’s problems can’t hide during a long run.

Running doesn’t necessarily cause injury. Instead, it points out weaknesses. Ignoring those weaknesses and continuing to run is what causes injury. This is something I learned after watching legendary runner, Joan Benoit Samuelson’s MasterClass.

Whether it’s tight hamstrings, inflammation in one hip, or a muscle imbalance, it needs your attention. Listen to your body and work to fix the small pains before they become a big injury.

According to our experience and experimentation, Man Flow Yoga is the best program for runners to strengthen their imbalances and weaknesses that cause injury. See our full experiment to see how 6-weeks of Man Flow Yoga improved mobility by 70% and total body strength by a wild 101%.

To avoid running injuries, do not ramp up mileage too fast or overtrain. Rest days and tapering before races are a must. Also, you need to crosstrain with lower body strength and mobility routines.

If you’re a beginner, do not skip this. According to one meta-analysis, novice runners are more than twice as likely to be injured compared to experienced runners. It’s best for all to follow a structured running program.

5. Running Changes Your Body Physique

The typical stereotype is that runners are rail-thin with little upper-body muscle. This isn’t necessarily wrong, but it doesn’t have to be the case.

If you look up images of a sprinter (like Usain Bolt) versus an ultramarathoner (like Scott Jurek), their different body types are striking.

This is attributed to the fact that sprinters utilize explosive, fast-twitch muscle and need immediate strength and power from their muscles.

Meanwhile longer distance runners (1 mile and up) rely on slow-twitch muscle and glucose energy reserves to get them through the race.

In other words, sprinters need more muscle.

Every type of runner will gain muscle and become more toned. The hips, glutes, and large muscle groups in your legs (quads, hamstrings, and calves) do most of the work.

Depending on what your goal is, you can use this to your advantage. As you build slow twitch muscle for long runs, your body will become leaner which is the route that Alex takes.

On the flip side, you can gain muscle and become more toned as a runner if you incorporate more sprints. This is what I did, and I also crosstrained with upper body, back, shoulder, and core workouts to maintain muscle mass.

During my marathon training, I did become leaner and more toned, but I didn’t lose my upper body muscle mass.

6. Thirst and Hunger Can Increase

Did you know that how you run affects your appetite and thirst?

After a typical run, I’m ready to wolf down everything in sight and Alex isn’t even hungry, only thirsty. Much of this depends on how your body reacts to a run: do you overheat? Do you sweat a lot? How fast did you run?

Research shows that a long, slow jog may increase your appetite more than a short sprint due to the change in temperature your body experiences.

Naturally, when you’re hot, your appetite is suppressed. On a run, Alex, who never seems to sweat ever, is drenched and reaches an incredibly high heart rate while I’m more at a steady state. Until you run, it’s hard to guess which category you might fall into.

This means that if your goal is weight loss, optimize how you run to burn the most calories, get in the longest workout, and manage your appetite. 

6. Stiffness and Injury Can Be Avoided

Yale Medicine estimates that 50% of runners will become injured every year. Who wants to run when you’re just a coin flip away from a frustrating injury and an expensive physical therapy bill?

This is something that we grapple with too, and our 50% injury rate looks like this: I’m often injured and Alex is never injured.

As we mentioned above, your body’s weaknesses can’t hide in the long run (see what we did there?). It’s important to address any stiffness or injury immediately.

For me, this meant incorporating more stretching, crosstraining with resistance bands, perfecting my running form, and using a foam roller for at least 10 minutes after every run.

My crosstraining regimen of choice included our Resistance Bands Workout Routine and a few favorite Beachbody On Demand workouts: Dynamix with Tony Horton from P90X3 and strength training with Idalis Velazquez’s 30-Day Breakaway.

If you don’t have a Beachbody On Demand membership, here is a list of their free workouts you can try, no strings attached. 

Do you want to run a marathon and not get injured? Follow our free 3-Month Marathon Training Plan.

3 Month Marathon Training Plan

The 3 & 4 Month Marathon Training Plan (PDF)

Download and get instant access to the printable marathon training schedule for beginners and intermediate runners.

Learn how to run a marathon in three months and not just finish, but have a positive experience and accomplish your goal. 

I want to learn more.

How running changes your MInd

When you start running, these are some mental and emotional changes you can expect.

Since all types of exercise come with an array of benefits — relieve stress, activate happiness hormones, improve sex drive, boost the immune system — we focus only on changes from running or jogging specifically. 

Also, these benefits are available to everyone, from Olympians to couch-to-5k participants.

7. Problem Solving and Creativity

“If you don’t have answers to your problems after a four-hour run, you ain’t getting them.

— From the must-read book, Born to Run by Chris McDougall

Clearer focus is one of exercise’s best benefits, but I think running takes it a step further. Typically, I enjoy running in silence. However, even when running with music (it does make you faster), it’s easy for my mind to wander and create new ideas. 

There’s something rhythmic and meditative about going on a long run — and your brain agrees.

Aerobic exercise, like going for a jog, stimulates new brain cell growth in the hippocampus. This region focuses on memory while the endorphins released during exercise have been linked to creativity. Together, you’re capable of better problem-solving.

8. Runnin’ Down A Dream Boosts Confidence

For many (me included), running a marathon is a huge achievement that sat stagnant on my bucket list for years.

While your dream may not be to run a marathon, what I love about running — and specifically running races — is that your progress is easily measurable.

Your mileage, pace, and distance are all opportunities to check off personal bests. And every time you do this, you become more and more confident with yourself and your body.

Something is amazing about looking at a map to the next town and thinking, “I could just run there.” And you don’t second guess yourself when tackling a long hike, summiting the next mountain, or exploring a new city on foot.

No matter why you run, running has been linked to improved self-esteem, mood, and focus. It’s a win-win-win all around.

If you run with your partner, this feeling you’ll share translates to improved relationship satisfaction. One of the many benefits or working out with your partner

Running FAQS

Running is an all-inclusive and highly customizable sport. If you’re a beginner, I am sure you have a lot of questions. The great thing about running is it gives you ample time to think. 

Rather than finding answers to your questions on the internet, it’s much more productive to take action and figure it out as you go.

Of course, if you have a specific question, Alex and I would love the opportunity to help. Feel free to ask away in the comments section of this article. 

Here are some common questions about running. 

How long does it take to see changes in your body from running?

It takes 1-3 months to see the changes in your body on the outside. If you want to see changes faster and track your progress more accurately, it’s best to use a body measurement chart.

However, running transforms your body (on the inside) and brain much faster. The ways running affects your body discussed in this article are activated after your first run. 

How does jogging change your leg shape?

Typically, when paired with proper nutrition, running will increase the size of your calf muscles and glutes especially, along with your quads and hamstrings. 

What does running a 5K do to your body?

Running a 5K is a great way to tone your body and become more physically fit. For best results, you need to follow a plan. The 30-Day Breakaway program (accessed through a Beachbody On Demand membership) is hands down the best. 

What is the best way to train for a marathon?

A marathon also requires an excellent plan, even more so than a 5K. It takes anywhere from 2-12 months to train for a marathon. You can learn how to train for a marathon in 3-4 months with our free Marathon Training Plans

Is running hills or stairs good for you?

Absolutely, all of our marathon training plans include hill runs. It’s an incredible way to build lower body strength and endurance.

Does running tone up your body?

During your run, track your total calories burned. Keep in mind, after you run you will continue to burn even more calories. 

A challenging run is a great way to ditch the love handles and help you lose belly fat. However, the word ‘challenging’ is key. If the workout doesn’t challenge you, it doesn’t change you. 

Your diet is also critical. If you burn 200 calories on a run and then devour 400 calories of leftover pizza immediately after, then no, running does not tone up your body. 

Instead, you will have what they call runner’s belly. To prevent this and tone your body, you need to know your calorie expenditure and consumption.

We recommend following our free 30-Day Weight Loss Challenge when you start running to keep your calories in check.

What’s better, a run of a workout?

That’s a great question. The answer is both. For years I only did the efficient and fast-paced workouts offered by Beachbody. They are insanely effective. 

However, running burns a ton of calories too and there are added benefits (like the ones shared in this article). We recommend a mixture of both. 

If you want to find out yourself, you can do our cardio experiment and see how your body responds!

Closing THoughts

Running is one of the most efficient and accessible ways to improve the health of your body and mind. We hope that learning how running changes your body will empower and motivate you.

There’s no better time than the present to start setting and achieving your goals!

Best of luck and focus on progress, not perfection. For more helpful resources, such as our Bodyweight Workout Plan or the 30-Day Ab Challenge, head over to our Work Out At Home page.

3 Month Marathon Training Plan

The 3 & 4 Month Marathon Training Plan (PDF)

Download and get instant access to the printable marathon training schedule for beginners and intermediate runners.

Learn how to run a marathon in three months and not just finish, but have a positive experience and accomplish your goal. 

I want to learn more.

30-Day Weight Loss Challenge Tracker Form V2 Ryan and Alex Duo Life

30-Day Weight Loss Challenge

As engineers with a combined twelve years of health coaching experience, we needed to create a data-driven way for our clients to sustain weight loss.

Too many weight loss challenges involve a long list of what you can, cannot, and need to do every day. We’ve reduced the overwhelm and only require you to track five numbers a day — calories, steps, fiber, sleep, and waistline.

You’ll track five numbers daily to give you the highest return for sustainable weight loss. As a bonus, we’ll share our Weight Loss Bundle, which includes strategies, progress tracking tools, and additional weight loss plans.

Learn more about the program.

As Seen In Feature Bar Ryan and Alex Duo Life

Hey we're Ryan and Alex

A husband-wife duo, two engineers, and the creators of Ryan and Alex Duo Life. 

After eight years working in the corporate world as engineers, we left our to tackle our true passion:

Helping highly motivated couples optimize their relationship and health by cutting through the muck and sharing what the research says works.

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