What will running do to your body?

Understand what running does to your body

If you have ever wondered what will running do to your body? the short answer is that it can reshape your health from head to toe. Regular running affects your heart, lungs, brain, muscles, bones, sleep, and even your mood. It can also help you lose weight and reduce your risk of serious disease, as long as you approach it at a pace and intensity that fit your current fitness and medical needs.

Below, you will see what happens to your body when you run, both in the moment and over time, so you can decide how to make running work for you.

Feel what happens during a run

When you start running, your body quickly shifts into “exercise mode.” You will notice changes within minutes.

Your breathing and lungs work harder

As soon as you begin to jog, your breathing rate increases to bring more oxygen in and push more carbon dioxide out. In healthy lungs, your breathing can rise from about 15 breaths per minute at rest to around 40 to 60 breaths per minute during moderate or vigorous running, which means your lungs may move close to 100 liters of air per minute to feed your working muscles (PMC).

Over time, as you keep running consistently:

• Your respiratory muscles get stronger
• Your lungs and body use oxygen more efficiently
• You need less effort to breathe at the same pace you used to find difficult (PMC)

If you have conditions like asthma or COPD, you can still benefit from aerobic exercise, but you need to adjust your pace and follow your doctor’s guidance, including using prescribed medications, to manage your breathing and symptoms safely (PMC).

Your heart pumps faster and more efficiently

During a run, your heart beats faster to push more oxygen-rich blood to your muscles and brain. This is a key part of cardiovascular conditioning. Running is highly aerobic and uses both carbohydrates and fatty acids for energy, which helps improve your overall cardiovascular fitness (PubMed).

If you keep up a running habit:

• Your resting heart rate often gets lower
• Your maximum oxygen consumption (VO₂ max) tends to increase
• Your heart becomes more efficient at pumping blood (PubMed)

Echocardiographic studies show that distance runners typically have larger and thicker left ventricles, which means each heartbeat can pump more blood. This “athlete’s heart” is now recognized as a healthy adaptation to regular endurance exercise, not a disease (PubMed).

Your muscles warm up and may burn

As you run, your body temperature rises, your muscles warm, and you start to sweat. At higher intensities, lactic acid builds up in your working muscles, which can cause that familiar burning sensation and fatigue. This is normal, and as you get fitter, your muscles become more efficient and produce less lactic acid at the same pace (ASICS).

Running uses nearly all the major muscles in your legs, especially the quadriceps, hamstrings, calves, and glutes. Regular running strengthens these muscles and improves endurance, and adding some strength training can further build muscle mass and support your joints (ASICS).

Your brain chemistry shifts

Even during your run, your brain chemistry starts to change. Your body releases endorphins and serotonin, which support mood and help you feel more positive and energized (WebMD). At the same time, your body begins to produce endocannabinoids, which are substances similar to those in cannabis. Unlike endorphins, endocannabinoids can cross into your brain and are likely responsible for the calm, relaxed feeling often associated with “runner’s high” (Johns Hopkins Medicine).

See how running changes your heart health

If you are asking “what will running do to your body?” your heart is one of the biggest winners.

Lower your risk of heart disease and early death

Regular running helps:

• Lower blood pressure
• Improve cholesterol levels
• Reduce strain on your heart by helping you maintain a healthier weight (ASICS)

These changes add up. A large 2014 study that followed more than 55,000 adults for 15 years found that runners had a 30 percent lower risk of death from all causes and a 45 percent lower risk of death from heart-related causes like heart attack or stroke compared with non-runners (University of Miami Health System). On average, runners in this study lived about three years longer than non-runners, and this benefit showed up even in people who ran slowly or infrequently.

Chronic endurance running also improves many coronary risk factors, which may help explain the link between long-term running and lower coronary death rates (PubMed).

Understand safe limits for extreme running

Moderate or vigorous running is generally very good for your heart. However, very high volumes like ultramarathons or running more than six hours per week may, in some people, lead to heart rhythm issues or heart muscle strain, especially if there is a history of arrhythmia or heart chamber dilation (University of Miami Health System).

Cardiologist Dr. Raul Mitrani recommends that if you regularly run more than six hours weekly, you should check in with your doctor and pay attention to symptoms like palpitations. If your doctor advises scaling back, you can still protect your heart with alternative moderate-intensity options like cycling, swimming, dancing, or walking (University of Miami Health System).

Use running to support weight loss

If you want to lose weight, running can be a powerful tool when you combine it with smart eating habits.

Boost your calorie burn and metabolism

Running is a high-energy activity. While you run, your body burns calories to power your muscles. Intense or longer runs also trigger an “afterburn” effect, where your body continues to burn extra calories for hours or even days afterward as it recovers (ASICS).

Running also increases your metabolic rate during and after your workout, which makes it harder for your body to store excess energy as fat (ASICS).

Improve your body composition and reduce visceral fat

Recreational running can have a strong impact on your body composition. A 2023 study of adults aged 18 to 65 in the Czech Republic compared people who ran at least 10 km per week with inactive adults. The runners, whose average weekly mileage was between 21.6 and 31.4 km, had:

• Lower body mass
• Lower body fat percentage
• Lower visceral fat
• Lower body mass index (BMI) (NCBI)

These differences were especially notable in older age groups. Runners also had a higher proportion of normal weight and much lower rates of overweight and obesity across all ages (NCBI).

Visceral fat, the deep abdominal fat that surrounds your organs, is particularly harmful because it is metabolically active and linked to serious metabolic and cardiovascular risks. The same study showed that visceral fat was significantly lower in runners of all ages, suggesting that running helps reduce a major driver of chronic disease (NCBI).

Slow age-related weight gain

As you age, your body mass, body fat, BMI, and visceral fat tend to creep up, even if your habits do not change. The 2023 study found that while aging affected both runners and inactive adults, the negative changes were slower or even reversed in older runners, which points to running as a way to slow age-related weight and fat gain (NCBI).

Strengthen your muscles and bones

Running does more than help you shed fat. It also builds a stronger, more resilient body.

Build stronger leg and core muscles

When you run, you use your:

• Quadriceps (front of thighs)
• Hamstrings (back of thighs)
• Calves
• Gluteal muscles (glutes)

Over time, running improves muscle endurance and strength in these areas. The glutes are particularly important for core strength, balance, weight management, and injury prevention in sports. Regular running optimizes glute function, which supports your posture and helps you stay more stable with each step (Cedars-Sinai).

You will see the best results when you pair running with strength training, especially for your hips, core, and legs, to support joints and improve performance (ASICS).

Increase bone density and protect against fractures

Running is a weight-bearing activity, which means your bones absorb impact and respond by getting stronger. Compared with walking, running stimulates greater bone-building activity. It encourages the release of hormones and enzymes like calcitonin, parathyroid hormone, and vitamin D, which help your body take up more calcium and build stronger bones (Cedars-Sinai).

With regular running:

• Bone density increases
• Your skeleton becomes more resilient
• Your risk of fractures and osteoporosis may go down over time

This makes running particularly valuable as you age, when bone loss typically accelerates.

Protect your brain and mental health

A big part of the answer to “what will running do to your body?” lives in your brain. The mental health benefits are significant.

Lift your mood and reduce stress

Running triggers the release of endorphins and serotonin, which support a better mood and a more positive outlook. Regular running can:

• Reduce symptoms of depression and anxiety
• Lower stress effects
• Improve self-esteem and productivity (WebMD, Cedars-Sinai)

Running outdoors can give you an extra mental health boost. Being outside has been linked to lower feelings of loneliness and isolation and to reduced stress levels, which can make you feel more connected and balanced (WebMD).

After your run, your body produces endocannabinoids, which cross the blood-brain barrier and help you feel calm, relaxed, and less anxious. Research suggests that these substances, more than endorphins, are probably responsible for the classic “runner’s high” feeling (Johns Hopkins Medicine).

Sharpen your memory and learning

Running is not only good for mood, it is also good for thinking and memory. Regular cardiovascular exercise like running is associated with:

• Neurogenesis, which is the creation of new brain cells
• Growth in the hippocampus, the brain region responsible for memory and learning
• Strong antidepressive effects by reducing the brain’s response to stress (Johns Hopkins Medicine)

Studies show that running can enhance brain performance and may help protect you from cognitive decline, including conditions like dementia and Alzheimer’s disease (ASICS).

Improve your sleep quality

After a run, your body temperature eventually falls and your brain chemistry settles, which encourages deeper and more regular sleep. Chemicals released during and after running help regulate your sleep cycle so you can fall asleep more easily and move through the stages of sleep in a healthier pattern (WebMD).

Distance runners often show:

• Better overall sleep
• Improved REM sleep, which is strongly linked to learning and memory
• Lower rates of depression and higher daily productivity (Cedars-Sinai)

When you sleep better, you are more likely to stay consistent with your workouts and make healthier food choices, which in turn supports weight loss and overall health.

Understand potential risks and how to run safely

Running is very beneficial, but like any physical activity, it is safest when you listen to your body and respect your limits.

Know when to talk to your doctor

You should check in with a healthcare professional before or while running if you:

• Have a history of heart disease, arrhythmia, or chest pain
• Experience palpitations, dizziness, or unusual shortness of breath while running
• Have lung conditions like asthma or COPD
• Plan to run at high intensity or for more than six hours per week

Doctors can help you tailor your running volume and intensity and may recommend periodic monitoring if you are training at a high level or have known heart issues (University of Miami Health System, PMC).

Adjust for environment and intensity

High-intensity running in very cold, dry air or in polluted areas can increase your risk of exercise-induced asthma or airway irritation, which may cause breathing problems after your workout (PMC). To reduce risk, you can:

• Start with an easy warm-up
• Cover your mouth and nose with a light scarf in cold air
• Avoid heavy outdoor exercise when air quality is poor
• Lower your pace or move your run indoors if breathing feels strained

If you build up your running gradually, include rest days, and mix in other activities like cycling or swimming, you support your heart and lungs while reducing the chance of overuse injuries.

Turn the benefits of running into a routine

Understanding what running will do to your body is the first step. The next step is to use that knowledge to build a routine that works for you.

You might start by:

1. Walking and adding short run intervals, such as 1 minute of easy running followed by 2 minutes of walking.
2. Aiming for at least 50 minutes of moderate running spread throughout the week, which is enough to improve heart health, muscle strength, and brain function (WebMD).
3. Choosing routes that feel safe and enjoyable, preferably outdoors, to get both physical and mental health benefits.
4. Pairing running with strength training and a balanced diet to support weight loss, muscle building, and bone health.

Over time, you will likely notice:

• Easier breathing at paces that once felt hard
• A calmer mind and more stable mood
• Better sleep and higher daytime energy
• Looser clothes and improved body composition
• Greater confidence in what your body can do

If you keep your pace realistic, pay attention to warning signs, and build up slowly, running can become a sustainable way to protect your heart, brain, and overall health for years.