Pushing the limit: Understanding the body’s performance at high elevation
A visitor flies into Denver from sea level, rents a car and drives up to Summit County. Braving the traffic, potholes and white-knuckle turns along the Interstate 70 mountain corridor, they get to one of the more amazing sights in Colorado: a dazzling blue Lake Dillon framed by the majestic Gore Range with rolling, green pine forests all around.
They decide not to waste any time, and they go for a hike as soon as they get here. Not too long into the hike, they start feeling a little lightheaded, and a headache starts gnawing at their temples. Farther along, their breaths get shorter. Before they’re halfway up, everything in their body is telling them to stop. They’re nauseated, dizzy and their muscles are aching.
Suddenly, their trip to the Colorado Rocky Mountains becomes a medical emergency.
What they’re experiencing is called altitude sickness, and it’s caused by hypoxia, a lack of oxygen in body tissue. Understanding hypoxia is the key to unlocking many mysteries of human health at elevation, including why so many people who live at high elevation are able to thrive.
In this first part of the Summit Daily News’ annual Longevity Project series, we explore how high altitude affects the biological and physiological processes, what performance gains the human body can experience after spending enough time at high altitude, and why some people — especially endurance athletes — thrive here.
Running out of air
Hypoxia can be acute or chronic and occurs when body tissue receives less oxygen then normal. At high elevations, about 8,000 or more feet above sea level, hypoxia occurs because there is lower barometric pressure. Lower pressure means less air drawn into the body with each breath, which also means less oxygen in the lungs. The towns of Breckenridge, Dillon, Frisco and Silverthorne are all above 9,000 feet, making them hypoxic environments.
Dr. Christine Ebert-Santos, a pediatrician who runs the Ebert Family Clinic in Frisco, has been studying the effects of high elevation on human health for two decades.
She said lower oxygen absorption in the lungs results in lower peripheral capillary oxygen saturation, measurable with a pulse oximeter, which in turn leads to lower oxygen saturation in red blood cells.
A pulse oximeter reading at sea level is normally at 100%. In Denver, peripheral capillary oxygen saturation is usually around 95-96%. Up in Summit, oxygen saturation is around 92%. Visitors coming to Summit from sea level might see their oxygen saturation drop to around 88% or lower before reaching levels typical at this elevation.
Any oxygen saturation level below 100% is considered low, while measurements in the mid-80s could be a real health concern. Below 80%, organ function is disrupted.
“If your oxygen saturation drops below 30%, you will probably die within a few hours,” Ebert-Santos said.
While people don’t drop dead from oxygen starvation in Summit, some do get very sick.
Charles Pitman, spokesman for Summit County Rescue Group, said his team goes out on calls all the time to help people who didn’t prepare properly for high altitude.
“People come up to altitude, but they don’t acclimatize. They drive up to Summit County and want to do a very arduous climb the next day,” Pitman said. “It takes three, maybe four days to acclimatize. By not allowing themselves to do that, they not only get tired, but they’re dehydrated and don’t use the best judgment.”
Pitman said the two primary indicators of a person experiencing altitude sickness are headaches and an inability to speak. He said people experiencing dehydration and altitude sickness often see the summit of whatever mountain they’re hiking, ignore the symptoms and push forward to their goal, making more poor decisions along the way. He said the rescue group has a term for that behavior: summit-itis.
“We’ve seen many cases of extreme dehydration over the years,” Pitman said. “When we find them, it’s very difficult to run a line to get fluids because their veins have collapsed.”
Pitman’s best advice for people coming up to high elevation from lower elevations is to be educated and to listen to their body.
“Don’t push yourself,” Pitman said. “A lot of people are short on time and try to maximize the number of things they’ll do, and it can be very challenging for them. We see that quite frequently. People need to take at least a day or two to acclimatize.”
For adventurers who want practical advice on how to avoid altitude sickness, there are few people on the planet with more experience or daring than mountaineer and explorer Mike Libecki, who was named a National Geographic Adventurer of the Year in 2013.
Libecki has conducted more than 90 expeditions to the North Pole, South Pole and many of the unexplored, untouched parts of the planet found in between — even places that have never been named. While he prefers technical climbing, Libecki is well-versed on what it means to perform at altitude, having climbed to 23,000 feet above sea level.
Libecki said the most important part of a high elevation trip is preparation and physical training — the parts he calls “easy.” Beyond that, it’s about staying hydrated, taking your time, and being cognizant about how everyone can get altitude sickness, no matter what physical shape you’re in.
“One time, our whole team went up a little too fast, and we had to go back down to 16,000 feet to get hydrated and adjust,” Libecki said. “It’s a pretty simple concept: Take your time. I’m not an Everest guy, but these high altitude climbs can be just as challenging as climbing it.”
Those seeking a high elevation panacea that will allow them to quickly acclimatize are out of luck — the human body just doesn’t work that way. Dr. Benjamin Honigman, director emeritus of the Altitude Research Center based out of the University of Colorado Anschutz Medical Campus, said that should not be the goal for people traveling to high altitude.
“I don’t think quicker is the idea. Safely is a better way to put it,” Honigman said. “The body takes some time to adjust. Trying to speed the process along is one of the factors predisposed to making people sicker. If you’re trying to focus on speed of acclimation, we don’t have ability to do that yet.”
Honigman said there are medications that can lessen the effects of altitude sickness. One such medication is acetazolamide, which is better known under the brand name Diamox. Honigman said medications can decrease the incidences of getting sick from as high as 30% to 5-8%.
As far as the most readily available remedies for altitude sickness — like those bottles of oxygen you can buy at mountain gas stations — they’re more or less useless.
“Those oxygen canisters might make people feel better for three or four minutes, but once off it, you’re back at altitude, so there’s no real utilization for them,” Honigman said.
The oxygen saturation level at which the body starts trying to compensate depends on a person’s hypoxia inducible factor, which varies by individual and is determined mostly by genetics.
“The hypoxia inducible factor is a protein complex that affects the body’s response to low oxygen by changing the expression of hundreds of genes in various ways, such as increasing the number of small blood vessels bringing oxygen to tissues,” Ebert-Santos said. “It’s a response to your body recognizing that it is not getting enough oxygen as it had been getting previously. If it goes on long enough, the body knows it needs to do something internally because it’s not getting something externally.”
Once the hypoxia inducible factor is activated, kidneys send out a hormone called erythropoietin, also known as EPO. Ebert-Santos said EPO can be detected in the body as soon as two hours after arriving at high elevation, showing how quickly human physiology reacts to oxygen level changes.
The EPO pushes a signal to the bone marrow, which is in charge of producing new red blood cells. The signal tells bone marrow that it needs to pump up its production of red blood cells and hemoglobin, the iron-based protein in red blood cells that absorbs and carries oxygen throughout the body.
The bone marrow obliges and starts sending more hemoglobin-rich red blood cells into the blood stream. These new cells, having a higher capacity for oxygen, compensate for the lower oxygen at altitude by carrying more oxygen away from the lungs to the tissue as they circulate.
Honigman said the hypoxia inducible factor and its regulation of EPO is a primary reason for how the body is able to acclimate to high elevation environments.
“The hypoxia inducible factor is a regulator of oxygen and how it is utilized in the cell,” Honigman said. “The factor upregulates EPO over time so that your body can adjust to lower amounts of oxygen in that environment.”
Ebert-Santos said that, while the EPO effect starts kicking in relatively quickly, it takes a while for the body to acclimatize to the point where it functions as normal with lower oxygen saturation. It might be a few days, or maybe even months, before the body feels like it is getting enough oxygen.
EPO and performance
Aside from helping the body acclimatize, EPO has a performance-boosting effect. An athlete with a higher red blood cell count and hemoglobin concentration won’t get fatigued as quickly and will be able to perform longer.
After Lance Armstrong was stripped of his seven Tour de France wins and banned from competitive cycling for life, EPO is one of the banned substances he admitted injecting into his body.
“My cocktail, so to speak, was EPO — but not a lot — transfusions and testosterone,” Armstrong said in his confession interview with Oprah Winfrey in 2013.
Roberto Ebert-Santos, Dr. Ebert-Santos’ son as well as a researcher and communications manager for the Ebert Family Clinic, has studied human performance at high altitude. He said the performance gains from a low oxygen environment can be offset by detrimental effects.
“There’s this misconception that training at high altitude is advantageous because of the oxygen deprivation, but it is so much more complex that,” he said. “The oxygen deprivation limits your performance in every other aspect. You can’t exert muscles to their fullest capacity because you will run out of respiratory stamina before you even get to the point where your muscles are tired.”
Because of the lower oxygen saturation, athletes never will be able to reach their maximum oxygen uptake level, expressed as VO2 max.
“Your heart and lung capacity is the limiting factor in training at high altitude,” he said.
That is why some athletes live by the “live high, train low” philosophy, where they live at high altitude to maximize blood oxygen efficiency and train at low altitudes to max out their workouts.
“‘Live high, train low’ centers around this philosophy that if you expose yourself for a certain amount of time to a high altitude environment, your body will create enough red blood cells to compensate for oxygen deprivation,” Roberto Ebert-Santos said. “But you want to train at low elevation to push your body to the extent you can allow your muscles to be challenged and grow.”
Dr. Ebert-Santos added that being born at high altitude provides some physiological advantages that can give a definite edge for endurance sports.
“Being born at high altitude gives an advantage for cardiovascular fitness,” she said. “People born at high altitude have larger lungs and higher lung capacity, which can certainly be an advantage for endurance sports. Muscles also develop more capillaries because there’s more circulation.”
High altitude performance
Summit County resident Nichole Sellon, 33, has been trail running since she was 22. Born in Los Angeles, Sellon doesn’t have the cardiovascular advantages of being born at high elevtion. When she first arrived in Summit County in 2015, Sellon said she experienced the same adjustment period others do when moving to high elevation.
“For the first six to eight months, I had the obvious signs. It was harder to exercise, as soon as I hit a hill, my breathing shot up a lot quicker than at sea level,” Sellon said. “I was more of a hiker the first six months than a runner.”
After she was fully acclimatized, Sellon embraced the high elevation life in Summit, with its endless trails to explore and ridgelines to ramble over. Her passion became her everyday workout, making her fit enough to do things at sea level most people would never dream of attempting.
In August, while visiting her father in Palm Springs, California Sellon decided on a whim to do the Cactus to Clouds hike, one of the steepest, most grueling hikes in the country. In summer 2009, three people died attempting what has been called “the hardest hike in America.”
The hike starts at 400 feet above sea level in downtown Palm Springs and ends at 10,833 feet at the summit of San Jacinto Peak. That’s more than 10,000 feet of elevation gain within 16 miles. San Jacinto Peak is the sixth most topographically prominent peak in the lower 48 states, meaning it is the sixth highest summit relative to the surrounding terrain.
The hike starts in the desert and ends at the top of a mountain, with temperature extremes at both ends. Sellon said it took her six hours to get to the peak.
“It went really well, and I think it’s because I live at altitude,” she said. “I felt strong, and it felt easy going the distance. I didn’t feel out of breath, and in fact felt like I had a lot more oxygen to work with. It’s definitely easier to do things at sea level than before I moved to Summit.”
Prinzhorn launched Grannies in the Bush 17 years ago. It’s now EduTek, a Colorado-based nonprofit.