How running changes your body
If you have ever wondered “what will running do to your body?” the short answer is that it can reshape far more than your legs. Regular running affects your heart, lungs, brain, bones, muscles, sleep, and even how you handle stress.
You do not have to become a marathoner to see benefits. Even a modest routine at a comfortable pace can improve your health and support weight loss, as several studies and medical centers report (WebMD, Cedars-Sinai).
Below, you will see what happens to your body when you start running, how your health changes over time, and how to stay on the safe side.
Immediate effects when you start running
What happens in the first few minutes
As soon as you begin to run your body jumps into action.
- Your breathing becomes deeper and faster so you can move more oxygen to your working muscles and brain
- Your heart rate rises to push more oxygen rich blood through your body
- You feel warmer as your muscles start generating heat and you begin to sweat to cool down
Johns Hopkins Medicine explains that this early increase in breathing and pulse is your body preparing for sustained exercise, not a sign that something is wrong (Johns Hopkins Medicine).
If you are new to running, this feeling can be intense at first. As your fitness improves, the same pace will feel easier because your heart and lungs become more efficient.
The “runner’s high” and your mood
You might have heard that running gives you a “runner’s high.” For a long time people thought this came from endorphins. Newer research suggests a different story.
While running does increase endorphins, these molecules do not easily cross the blood brain barrier. Johns Hopkins Medicine notes that endorphins are unlikely to be the main cause of the post run euphoria or calm feeling (Johns Hopkins Medicine).
Instead, the credit likely goes to endocannabinoids, chemical substances your body produces that can enter the brain and have short term psychoactive effects. After a run, these endocannabinoids can help you feel:
- Calmer
- Less anxious
- More relaxed
Both WebMD and Johns Hopkins report that this shift in brain chemistry helps you manage stress and feel mentally lighter after a workout (WebMD, Johns Hopkins Medicine).
Long term changes to your heart
How running strengthens your heart
If you keep asking “what will running do to your body?” your heart might be the most important answer. Running is a highly aerobic activity that conditions your cardiovascular system by using both fats and carbohydrates for fuel (PubMed).
Over time, regular running can:
- Improve how efficiently your heart pumps blood
- Lower your resting pulse rate compared with being sedentary
- Increase your maximal oxygen consumption, a key marker of cardiovascular fitness
Echocardiographic studies show that distance runners tend to have larger and thicker left ventricles than people who do not exercise regularly. This adaptation, sometimes called the “athlete’s heart,” lets the heart pump more blood with each beat and is now seen as a healthy response to training rather than a disease (PubMed).
Heart health and longevity
Running is consistently linked to better heart health over the long term. The University of Miami Health System highlights a 2014 study that followed more than 55,000 adults for 15 years. Compared with non runners, runners had:
- About a 30% lower risk of death from any cause
- About a 45% lower risk of dying from heart related causes, including heart attack or stroke
- An average life expectancy roughly three years longer
These benefits showed up regardless of speed or how often people ran. Even slow or infrequent running reduced risk when compared with not running at all (University of Miami Health System).
Long term running also improves several coronary risk factors. Studies suggest that these improvements may help explain the link between running and lower rates of death from coronary causes (PubMed).
When more is not always better
Although running generally supports heart health, very high volume training can carry some risk. The University of Miami notes that extreme long distance events and ultramarathons might lead to heart damage or rhythm problems in certain people, especially those with a history of arrhythmia or dilated heart chambers (University of Miami Health System).
Cardiologist Dr Raul Mitrani suggests that if you run more than six hours per week, it is wise to talk with your doctor, particularly if you notice palpitations or know you have heart rhythm issues. If you need a lower impact option, moderate intensity activities like cycling, swimming, dancing, or walking can still protect your heart (University of Miami Health System).
Effects on your lungs and breathing
How your breathing adapts
When you run, your breathing rate can climb from about 15 breaths per minute at rest, which equals roughly 12 liters of air, to around 40 to 60 breaths per minute, about 100 liters of air, in healthy lungs. This change allows your body to bring in more oxygen and remove more carbon dioxide to meet the demands of your working muscles (PMC).
With consistent training, your muscles become more efficient, so they:
- Need less oxygen for a given effort
- Produce less carbon dioxide
That means over time you can run at the same pace with easier, more comfortable breathing, because your respiratory system does not have to work as hard (PMC).
Running with lung conditions
If you have asthma, COPD, or another lung condition, running can still be part of your life. Research notes that people with respiratory issues can benefit from running as long as they:
- Follow medical advice
- Use prescribed inhalers or medications
- Adjust their pace and distance to their capacity
These steps can help you improve breathing capacity and manage symptoms while staying active (PMC).
Potential breathing related risks
The environment where you run matters. High intensity training in cold, dry air or polluted conditions can increase the risk of exercise induced asthma or bronchial hyperresponsiveness. This can lead to airway narrowing after exercise (PMC).
If you notice wheezing, chest tightness, or coughing that worsens after runs, especially in cold or polluted air, it is important to discuss these symptoms with a healthcare professional.
Changes in weight and body composition
How running supports weight loss
If your main question is “what will running do to your body?” in the context of weight loss, the answer is encouraging. Running is a powerful tool for changing body composition because it burns calories during the workout and can keep your metabolism elevated afterward.
ASICS describes how running:
- Raises your heart rate and calorie burn immediately
- Elevates your metabolic rate during and after the run
- Extends the “afterburn” effect, especially with higher intensity runs, so you burn more calories for hours or even days afterward
This higher energy use makes fat accumulation less likely if your calorie intake is balanced (ASICS).
Impact on body fat and visceral fat
A 2023 study in the Czech Republic looked at adults aged 18 to 65 who did recreational running, at least 10 km per week, and compared them to inactive people. The average runner in the study actually logged between 21.6 and 31.4 km per week. Runners had:
- Lower body mass
- Lower overall body fat
- Lower levels of visceral fat in all age groups
Visceral fat is the deeper fat that surrounds organs and is linked to metabolic problems and cardiovascular risk. Having less of it is strongly associated with better long term health (NCBI).
Compared with inactive individuals, runners also:
- Had lower body mass index
- Were more likely to fall in a normal weight range
- Showed markedly lower rates of obesity in every age category
The researchers observed that although aging tends to increase weight and fat in both runners and non runners, runners had smaller increases or even decreases in these measures as they got older. That suggests running can slow down some of the usual, age related shifts in body composition (NCBI).
How running shapes your muscles and bones
Muscle strength and tone
Running engages nearly all the muscles of your lower body. ASICS points out that regular running particularly works your:
- Quadriceps
- Hamstrings
- Calves
- Gluteal muscles
For beginners, leg strength and endurance can improve quickly because these muscles are used repeatedly and under load. Running is especially effective at optimizing your glutes, which support core strength, balance, and stability. Strong glutes also help with weight loss efforts and may reduce the risk of sports related injuries (ASICS, Cedars-Sinai).
If you want visible muscle size in addition to tone, adding targeted strength training to your routine is recommended, since running alone is better for endurance than for building large muscle mass (ASICS).
Stronger bones and joint support
Running is a high impact, weight bearing activity. That impact can be beneficial for your bones when approached sensibly. Cedars-Sinai explains that running stimulates bone building hormones and enzymes, including:
- Calcitonin
- Parathyroid hormone
- Vitamin D related processes that improve calcium uptake
These responses help increase bone density, and studies find that runners have higher bone density than walkers. Stronger bones can reduce your risk of fractures as you age and may be particularly important if you spend much of your day sitting (Cedars-Sinai).
For your joints, the story is more nuanced. Healthy joints can adapt to running when you:
- Increase mileage gradually
- Wear appropriate, supportive shoes
- Vary terrain and surfaces
- Include strength and mobility work
Listening to early warning signs like persistent joint pain is key so you can adjust your plan before minor irritation becomes an injury.
Effects on your brain and mental health
Brain function and protection
Running is not just about your body shape. It also changes how your brain works.
WebMD reports that regular running at a moderate or vigorous pace can improve mental health, memory, and learning ability. It does this in part by increasing serotonin levels, which support a more stable mood and better sleep (WebMD, ASICS).
Johns Hopkins Medicine notes that regular cardiovascular exercise like running promotes neurogenesis, the creation of new brain cells, in certain regions of the brain. Running has also been shown to increase the size of the hippocampus, a key area for memory and learning. These changes may help protect against cognitive decline and conditions like dementia and Alzheimer’s disease (Johns Hopkins Medicine, ASICS).
Mood, anxiety, and loneliness
If you deal with stress, low mood, or anxious thoughts, running can be a helpful tool in your mental health kit.
According to WebMD, running:
- Triggers the release of endorphins and serotonin that enhance mood
- Reduces stress and helps modulate how your body responds to it
- Lowers the brain’s response to physical and emotional stress
- Can reduce symptoms of depression and anxiety
- May ease feelings of loneliness and isolation, especially when you run outdoors (WebMD)
Cedars-Sinai adds that distance runners often report lower rates of depression, higher self esteem, and greater productivity compared to people who do not run regularly (Cedars-Sinai).
Sleep, energy, and daily wellbeing
Better sleep patterns
Running often improves how you sleep at night. WebMD notes that chemicals released during and after running encourage deeper sleep and a more regular sleep schedule (WebMD).
Cedars-Sinai points out that distance runners tend to have better sleep cycles with improvements in REM sleep, the sleep stage that is associated with learning and memory processing (Cedars-Sinai).
You may notice that once running becomes a habit you:
- Fall asleep faster
- Wake less often in the night
- Feel more rested and alert the next day
Energy, focus, and productivity
Although running uses energy, it often gives more back in return. By improving cardiovascular fitness, body composition, and sleep quality, running can leave you feeling more energetic in everyday life.
People who run regularly often describe:
- Clearer thinking and better concentration
- Greater resilience during stressful workdays
- A more stable, upbeat mood
These shifts are supported by the mental health and brain function benefits seen in the research from WebMD, Johns Hopkins, and Cedars-Sinai.
Health risks running can help reduce
Chronic disease prevention
Regular running is associated with a lower risk of several major health issues. Research summarized in the PMC article on exercise and lungs states that consistent physical activity, including running, reduces the risk of:
- Stroke
- Heart disease
- Type II diabetes
- Depression (PMC)
Combined with findings from the University of Miami and PubMed about heart health and coronary risks, the pattern is clear. Making running a regular part of your life can play a big role in preventing or delaying chronic conditions that often appear with age.
Metabolic health and weight related risks
The 2023 Czech study shows that runners have lower body mass, body fat, and visceral fat compared to inactive peers. Since visceral fat is linked to metabolic disturbances and cardiovascular disease, lower levels are a strong sign of better metabolic health (NCBI).
Running also helps decrease strain on your heart by improving cholesterol, lowering blood pressure, and supporting weight management, all of which reduce the likelihood of cardiovascular problems over time (ASICS).
Staying safe while you enjoy the benefits
How to ease into running
Knowing what running can do to your body is only helpful if you apply it in a way that fits your current fitness and health. To start safely you can:
- Begin with a walk run approach, for example 1 minute of easy jogging followed by 2 to 3 minutes of walking, repeated several times
- Run at a pace where you can still speak in short sentences rather than gasping for air
- Increase your total weekly distance by small amounts instead of making big jumps
- Include at least one rest or cross training day between harder runs
This gradual approach lets your heart, lungs, muscles, bones, and connective tissues adapt so you gain benefits with a lower risk of overuse injuries.
When to talk to a doctor
It is wise to check in with a healthcare professional before starting or ramping up a running routine if you:
- Have a history of heart disease, arrhythmias, or chest pain
- Notice palpitations, dizziness, or unusual shortness of breath during or after runs
- Live with a chronic lung condition and are unsure how hard you should push
- Plan to train for very long distance events or run more than six hours per week
As Dr Raul Mitrani recommends, monitoring your heart health is especially important if you push into higher volumes of endurance training (University of Miami Health System).
Bringing it all together
When you ask “what will running do to your body?” the honest answer is that it touches nearly every system you have. With consistent, moderate running you can:
- Strengthen your heart and improve circulation
- Train your lungs to work more efficiently
- Reduce body fat, especially harmful visceral fat
- Build stronger bones and more resilient muscles
- Enhance memory, learning, and protection against cognitive decline
- Lift your mood, ease anxiety, and improve sleep
- Lower your risk of stroke, heart disease, type II diabetes, and depression
You do not need perfect form, special talent, or a long history of athletics to begin. You just need a starting point that matches where you are today.
Try lacing up for a short, gentle session this week, even if it is mostly walking with a bit of easy jogging. Then pay attention to how your body and mind feel in the hours and days afterward. Little by little, the benefits will add up.
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