Grand Canyon Rim-to-Rim Hikers Give their Sweat and Blood to Science

Jun 13, 2017

The Grand Canyon’s rim-to-rim trail is not an ordinary day hike: a marathon in distance, a mile change in elevation, through a desert that swings through extremes of heat and cold. Rim-to-rim hikers put their bodies through a grueling experience. That makes them the perfect candidates for a study aimed at predicting medical emergencies before they start. KNAU’s Melissa Sevigny reports. 

Rim-to-rim hikers start their journey at the South Kaibab trailhead
Credit Melissa Sevigny


It can be dangerous to hike the Grand Canyon one side to the other in a day. Dr. John Femling of the University of New Mexico knows that. He leads a research study on the physical trauma endured by rim-to-rim hikers. One day in the canyon, he witnessed it firsthand.

“We were about a mile and a half from the end,” he remembers. “There’s this young kid, laying on the side of the trail not doing well.”

Femling stopped to help. Moments later, the young man had a seizure.

“Now you aren’t anywhere close to anything, and you have a young otherwise healthy kid whose brain is no longer working,” Femling says.

He had hyponatremia, a common problem in the canyon when people drink too much water. Femling says it was a profound reminder of why his research is needed. Some weekends, more than a thousand people hike the canyon rim to rim. They’re not always prepared. Femling and his colleagues want to pinpoint the earliest possible warning signs that someone’s health is about to take a bad turn.

Hikers volunteer for the research study at the South Rim
Credit Melissa Sevigny

Glory Emmanuel Aviña, psychologist at Sandia National Laboratories, says, “What we’re really interested in is: what is the point you need to sit down and take a five-minute break, and you’ll be fine to go the rest of the way, or: you need to stop and get some serious help, because you’re about to have a very catastrophic health occurrence.”

The research will help Grand Canyon visitors, but also others who experience trauma: extreme athletes, car accident victims, even military personnel. Aviña wants to use the data to design a better fitness device for soldiers to wear. She says it makes sense to study rim-to-rim hikers.

“The canyon is kind of a natural experimental design environment, because once you go down you must come up. All of our hikers have to come up out of the canyon,” she says.  

This means they’re bound to stress out their bodies. New Mexico researcher and former park ranger Emily Pearce says most people are a little bit sick by the time they reach the other side. “We really wanted to understand more physiologically about what was happening to people at the canyon… down at the cellular level.”

A bus brings the day’s first hikers to the South Kaibab trailhead before dawn. They’re eager to get going, but some agree to participate in the study. Pearce calls out instructions to the crowd: “We’re going to weigh you, we’re going to weigh your pack, we’re going to take a small sample of blood.”

Julie Cusumano from Portland is here for her second rim to rim hike. She answers a researcher’s questions about her eating, sleeping and exercise habits. Then she’s given a fitness device to track her heart rate, and plays a simple “brain game” on an iPhone. She’ll play it several times during the hike to see how fatigue affects decision making skills.

A group of rim-to-rim hikers about to start down the trail
Credit Melissa Sevigny

Finally, she gives a blood sample before setting off. “It’s for science!” she says. 

Preliminary results suggest just a couple of questions and simple tests early in the hike can predict how someone will feel at the end. That’ll be useful to park rangers like Ben Cooper, who leads Grand Canyon National Park’s preventative search and rescue program. He wants to be able to identify people in trouble, before the trouble starts.  “That prevents potentially 12 to 16 rangers from hiking down trail and carrying this person out with a true medical emergency,” he says. 

Cooper says on average 300 search and rescues take place in the canyon every year. He hopes this research can change that. “We’re getting good data from this study that will hopefully give us a little more insight into proper hydration, exertion, which is huge. We’re really trying to get an understanding of what happens to the human body out here,” he says.

The study is in its third year and has enrolled 1,200 hikers so far. Today’s group sets off down the trail. They’ll do all the tests again when they reach the North Rim.