( ) 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. 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. 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.
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