Published October 22, 2026 03:05AM
This article has been medically reviewed by Rachel MacPherson, a certified strength and conditioning specialist, an ACE-certified personal trainer, and a PN1-certified nutrition coach.
It’s time for science to remind you that exercise—especially outdoor activities like hiking—is good for you, and a recent study offers some clues as to why.
The study, published in Scientific Reports, had 34 previously sedentary South Korean adults aged 66 to 78 go hiking in a forest for 120 minutes twice a week for three months. Compared with a control group that did no physical activity, the hikers showed reduced body fat, increased muscle mass, and higher aerobic capacity. The hikers also showed a reduction in inflammation markers and an increase in interleukin-12 (IL-12), a protein that activates natural killer cells (NKC), which are white blood cells that destroy infected or abnormal cells, including cancer cells.
“Being outdoors has a significant impact on mood and stress levels. If we can get people exercising outdoors, we are able to see more stacked impacts of whatever they’re doing physically and [that includes] the mood and mental health side that comes with it,” physical therapist Milica McDowell, DPT, told Outside.
Based on this study, it’s not clear how hiking may impact a person’s immune system long-term, but hiking can still offer plenty of benefits on this front. McDowell said your immune markers are generally tied to inflammation levels—when you reduce inflammation in your body, you improve your immune function. She noted that exercise can also improve sleep, reduce stress, and lower cortisol levels, all of which help decrease inflammation and boost immune markers.
So what exactly happens inside your body when you hit the trails that makes hiking so beneficial? Here’s what McDowell, along with exercise scientist Domenic Angelino, CSCS, CPT, exercise physiologist Chris Anderson, PhD, and hiking trainer Alicia Filley had to say.
Each Breath You Take Brings More Oxygen to Your Lungs and Blood
When you exert yourself during a hike, the body needs more oxygen to power itself. But obtaining it isn’t actually as easy as just breathing, Anderson, an exercise physiologist and senior lecturer at Torrens University, told Outside.
Once a person breathes in an oxygen molecule, it needs to contact a red blood cell in their lungs to oxygenate it, which can then carry that oxygen to the rest of their body. If you have more capillaries—small blood vessels that transport oxygen and nutrients around the body—you have a higher capillary density (CD) in your working muscles. A higher CD increases the amount of oxygen that can be transported to tissues and cells in the body.
As your lungs are challenged during hard exercise, they open up more of those tiny blood vessels they already have so oxygen has more surface area to cross into the blood, Anderson said. Over time with regular training, your muscles grow more capillaries, so oxygen has a shorter distance to travel from blood into the muscle cells that need it. Training also strengthens the muscles that power your breathing, which helps you move more air with each breath, he said.
All of this ultimately improves measures like your VO₂ max, which measures your maximum aerobic capacity via how much oxygen you can consume per unit of time, according to Angelino.
The Heart Pumps Oxygenated Blood Throughout the Body
The way that oxygen gets from your lungs to the rest of the body is via blood pumped by your heart. As your body’s workload increases, your heart has to pump faster or harder to distribute that oxygen. As soon as you hit the trail and get moving, your heart kicks into higher gear.
Training changes the heart itself, Anderson said. When you do aerobic training regularly, the heart’s chambers get larger and fill more completely, and your blood volume increases, so each beat delivers more blood. This is known as “the athlete’s heart,” and it’s a healthy, reversible adaptation (as opposed to the heart enlarging from high blood pressure or disease, which is harmful).
Those extra capillaries your working muscles grow from exercise also let them pull oxygen out of the blood more efficiently. In one 12-week study, participants who took place in vigorous exercise saw their VO2 max rise about 20 percent, as well as increases in the volume of blood pumped both per minute and per heartbeat (stroke volume and cardiac output) and muscle CD. When you’re hiking, this will mean your heart has to beat fewer times and can do more at the same pace.
Your Muscles Use That Oxygenated Blood for Energy
Once the oxygenated blood reaches your muscles, they use that oxygen to produce energy. Muscles deprived of oxygen during exercise will also grow more blood vessels so that next time they need energy, more muscle can receive oxygenated blood, Anderson explained. That means the next time you’re toiling up a switchback or hefting your backpack, your muscles may get oxygen more efficiently and fatigue more slowly, making the task easier.
Strength-wise, how much muscle you build from hiking depends on your baseline fitness level. In the study, participants were previously doing zero physical activity, so the hiking put enough strain on their bodies to reach the overload threshold, McDowell noted, where the body is under sufficient stress to induce muscle growth.
“Overload comes in many forms,” McDowell told Outside. “If you’re somebody who is not active, you can get to overload with hiking.”
Even if you are more active, you can still increase the difficulty of your own hikes to push you to that overload threshold by adding challenges like weight, incline, and elevation, Filley said.
Hiking Helps Circulate More Blood to Your Brain
Angelino also said more blood circulates throughout your body when you hike, including to your brain, which benefits cognitive health.
Plus, the forest is full of exciting new information. The Scientific Reports study also notes that trees release phytoncides, chemicals that protect them from animals and microbes, that may help reduce inflammation and support immune function when inhaled.
“Being in an environment where you interact with unexpected stimuli is a very special part of being in the forest and being outdoors,” McDowell said. When you take in new information, like a rare insect on the trail or an unusual bird call, you engage your brain’s capacity to form and strengthen neural connections, known as neuroplasticity. Improved neuroplasticity means better brain function, which is necessary to help you remain vigilant and focused so you can adjust and quickly respond to changes in the environment while you’re outdoors.
“Hiking is a great activity, and it’s a great exercise,” Filley said. “It can absolutely have health benefits. If you enjoy it and you have access to it, get out and do it.”
About the medical reviewer: Rachel MacPherson has spent over a decade helping lifters trade bro science for actual results. She’s happily turned an obsession with evidence-based health into a full-time writing and strategy career, helping publications, wellness brands, and supplement companies tell smarter stories that people trust. She’s a stickler for science-backed training advice that respects the reader’s intelligence, with the ultimate goal of getting you under the bar with total confidence (or moving in whatever way feels best).
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