As many as 30 million people travel to the mountains in the western United States each year¹ to enjoy the beauty and outdoor activities the terrain has to offer. Travelers may worry about altitude sickness upon arrival. However, another important side effect of high altitude exists: muscle atrophy. While it may not be noticeable during visitors’ short time at high altitude, it is still a remarkable effect the elevation has on human bodies.

Muscle atrophy is a scientific term for the loss of muscle mass²; essentially, the muscle fibers shrink due to loss of important contractile proteins and organelles, which are essential parts of muscle fibers³. This means that the muscle won’t be able to perform as well⁴, especially in terms of endurance and power; tasks that are normally easy, such as walking up a flight of stairs, may be significantly more tiresome or difficult.

An elevation is considered high altitude when the location is 2400 meters or more above sea level⁴. This is about 7,874 feet of elevation. Over 140 million people worldwide live at or above this altitude⁴, making the issue of altitude-induced muscle atrophy very relevant to many. 

Hypobaric hypoxia, which occurs at high altitudes, is a decreased barometric pressure in addition to a decrease in oxygen availability¹. This is a double whammy for visitors for two reasons: a lower pressure won’t be able to push as much oxygen into tissues, and less availability of oxygen will diminish the amount that tissues receive¹. These two conditions result in less oxygen getting to body systems¹ that usually obtain a good amount. This is especially pertinent to muscles because of their prevalence in the human body.

Muscle atrophy is indicative of a disproportion between the process that builds protein and the process that breaks down protein in muscles². Several studies have shown that when muscles receive less oxygen, such as in hypobaric hypoxic states, muscle protein degradation is boosted while muscle protein creation dwindles^2,3,4,5. This results in an overall deficit of protein in the muscle, which is meaningful because muscles store the most protein compared to any other organ in the body³.

Currently there are no official guidelines for prevention of muscle atrophy due to hypobaric hypoxia. There are also no medications that currently counteract the loss of muscle³, although researchers are now turning their focus to ways of maintaining the balance of protein breakdown and building in muscle. 

Despite the fact that these measures are suggested for preventing high altitude illness, it may be beneficial in general to stay hydrated, ascend slowly to altitude, eat a balanced diet, and remain active¹. Foods and herbal supplements rich in antioxidants may be helpful in preventing muscle wasting during exposure to hypobaric hypoxia⁴, although there is no direct evidence to support this theory yet. Overall, it would be beneficial to maintain good nutrition throughout the visit to the mountains. Moderate exercise may help visitors acclimatize, although overly spirited exercise can cause other altitude-related problems¹.

How are people who live at altitude affected by muscle atrophy? At the moment, studies are geared more towards the effects that altitude has on people who visit from lower elevations. Once the body has acclimated to the altitude, oxygen utilization and distribution will improve greatly and will ensure that tissues receive more oxygen¹. This may explain why people who live at high altitude for long periods of time are able to maintain and oftentimes increase their muscle mass. Even so, people who live at high altitude should still eat a healthy diet and drink a good amount of water to make sure their bodies can function optimally.

It is important to be aware of the side effects that altitude has on the bodies of sea-level visitors. There is still more research to be done regarding effective treatment options for this particular type of muscle atrophy. Knowing that high altitude causes muscle atrophy can help people be aware of their activity level and diet and may modify how people choose to ascend to the mountains. This consequence of high altitude should not prevent people from enjoying all that mountainous regions have to offer.

Grace Barrett is a Physician Assistant student at the University of St. Francis in Albuquerque, New Mexico. Born and raised in Grand Rapids, Michigan, Grace attended Michigan State University where she received degrees in both Physiology and Spanish. After completing her rotation in pediatrics with Dr. Chris, Grace will have rotations in New Mexico, Michigan, and California before graduating in April 2020. She is hoping to explore urology as her elective rotation. Grace enjoys baking cookies, being active, watching Chopped on the Food Network, spending time with family, and planning her wedding (in August 2020). 

References

1. Gallagher SA, Hackett P, Rosen JM. High altitude illness: Physiology, risk factors, and general prevention. UpToDate. https://www.uptodate.com/contents/high-altitude-illness-physiology-risk-factors-and-general-prevention. Published September 20, 2017. Accessed July 18, 2019.

2. McKinnell IW, Rudnicki MA. Molecular Mechanisms of Muscle Atrophy. Cell Press. 2004;119:907-910.

3. Bonaldo P, Sandri M. Cellular and molecular mechanisms of muscle atrophy. Disease Models & Mechanisms. 2013;6(1):25-39. doi:10.1242/dmm.010389.

4. Rathor R, Suryakumar G. Muscle Atrophy at High Altitude. Journal of Clinical and Molecular Endocrinology. 2016;1(3):1-2. doi:10.21767/2572-5432.10018.

5. Chaudhary P, Suryakumar G, Prasad R, Singh SN, Ali S, Ilavazhagan G. Effect of acute hypobaric hypoxia on skeletal muscle protein turnover. Al Ameen Journal of Medical Science. 2012;5(4):355-361.