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Anna Frost at the finish line of the Hardrock 100, after struggling through a nighttime chill that nearly cost her the race. Photo by Paul Cuno-Booth

Three-quarters of the way through the Wasatch Front 100 Mile Endurance Run, my ability to run or hike fluidly degenerated into a slow-motion, stiff stagger, as if I were struggling to summit Everest rather than merely ascending a 10,400-foot peak on a clear but chilly night.

I couldn’t feel my hands. I couldn’t think clearly. I could barely—just barely—keep my eyes open.

On the verge of passing out while pausing between each clumsy footstep, I felt as if I were gradually freezing. My pace? A glacial 45 minutes per mile. If not for my pacer’s encouragement and the rejuvenating sunrise, I’m fairly certain I would have curled up on the trail to take a nap and required rescue.

On mountainous trail runs or in harsh winter conditions, especially over ultra distances, a perilous combination of factors can lead to a loss of warmth and mobility, and to an increase in confusion and fatigue.

This pre-hypothermic state doesn’t have to progress to actual hypothermia—defined as body temperature dropping from a normal of 98.6 degrees to below 95—to put the runner in significant danger. Just getting chilled, clumsy, confused and sleepy heightens the risk of falling down, getting lost or losing consciousness.

While wintertime obviously makes staying warm more challenging, trail runners are at risk for hypothermia year round—sometimes, ironically, more so in summertime, if they hit the trail in sunshine lightly dressed and underprepared for changing weather or nightfall.

Shifting weather makes runners in the high country especially prone to hypothermia. Photo by Paul Cuno-Booth

Anna Frost of New Zealand suffered through this state of pre- or mild hypothermia during the Hardrock 100 Endurance Run last July, which nearly cost her the race.

Traversing the 13,000-foot passes near Telluride, Colorado, Frost says her legs lost their ability to run and could only manage a “slow slog.” She became increasingly cold, sleepy and “spaced out,” to the point where she didn’t care when Darcy Piceu, the eventual second-place finisher, passed her.

“I was totally out of it,” Frost recalls. “If I had been on my own”—without a pacer—”I would have laid down to sleep, and I think I would have frozen there forever.”

Instead, with the encouragement of her crew and pacer, she ingested some food and caffeine, and put hand-warmer packets down her bra and in her gloves. Taking these small but important measures enabled her to stay awake and keep moving until she reached a lower altitude and warmed up in the sun. She went on to win the race.

Knowing how to prevent this feeling of freezing, and how to troubleshoot the early symptoms of hypothermia, can save your race (and maybe even your life).

Understand the Risks

To prevent hypothermia, you must do one of two things: generate heat, which requires movement and calories; or retain heat, which requires insulation from clothing. It sounds simple. So why do so many trail runners fail to generate or retain enough heat?

Usually, it’s because they don’t recognize and prepare for several risk factors. Any of these factors may threaten your ability to stay warm and alert:

  • High altitude: Thinner air contributes to a slower pace due to an elevated heart rate. High altitude also can trigger nausea and dehydration, which negatively affects energy metabolism.
  • Nighttime: Darkness generally slows runners down and makes them sleepier.
  • Inclement climate: Mountain ranges especially are notorious for fast-changing and severe weather. Clouds suddenly blot out the sun and produce downpours.
  • Unfamiliar terrain: If you’re new to the area, you’re at a greater risk for getting lost or for taking longer than anticipated, meaning prolonged exposure and possibly running out of calories.

Moreover, runners don’t realize how the potential difficulties, if they come to pass, “can dog-pile on one another,” says seasoned ultrarunner and coach Jason Koop, director of Carmichael Training Systems in Colorado Springs, Colorado.

“It’s very rarely one triggering thing” that puts a trail runner or hiker at risk for hypothermia, Koop explains. “Your body will adapt to one or two different stresses. It’s when you have multiple ones”—such as wet weather, a calorie deficit caused by gastrointestinal distress, exhaustion and perhaps an unexpected discomfort, such as a blister, that inhibits movement—“and those multiple factors all reinforce each other,” making it harder physically and psychologically to cope with the situation.

Several compounding factors pushed Rachel Bell Kelley of Chapel Hill, North Carolina, toward exhaustion and hypothermia at the 100-mile Run Rabbit Run in Steamboat Springs, Colorado, last September and resulted in her first DNF.

“I had enough blood flow to do one or two important things, but not all at the same time,” she recalls. “If I ate, I had to slow down and got colder. If I didn’t eat, I had a lack of calories. I chose to move instead of eating. … I wanted to eat so badly, but I felt nauseous, and I had an overwhelming sense of being tired. My eyes were so heavy, I just wanted to put my head down for a minute.”

Recognize and Address the Symptoms

About halfway through Run Rabbit Run, Kelley experienced common early warning signs: numb fingers that made it difficult to zip her jacket, chattering teeth and confusion over whether she was going the correct way. Then nausea hit.

“It was like my neurons and muscles weren’t working well. I wasn’t quite dragging my feet, but wasn’t picking them up either,” she says. “I was uncomfortable, but I was thinking, ‘This is part of a 100-miler; suck it up.’”

Recognizing symptoms that signal a slide toward hypothermia can help you aggressively troubleshoot them, rather than ignoring them or trying to “tough it out.” They include:

  • Shivering: If your limbs shake or teeth chatter, it’s a sign your body is trying to protect itself by generating heat through involuntary shivering.
  • Loss of dexterity: With numb fingers and toes, you might unwisely decide not to take off your pack to access calories or extra clothing because you feel it’s too difficult to fumble with your pack’s fastenings.
  • Stiff and unresponsive legs: Cold and fatigued, your legs lose their ability to run or hike efficiently. Your gait becomes a shuffle or stagger, increasing the risk of catching a toe and tripping.
  • Feeling dizzy or lightheaded: Often caused by insufficient calories or high altitude’s thinner air, feeling lightheaded will slow you down.
  • Increased urination: You may need to pee repeatedly due to cold diuresis, a condition that occurs when blood flows from extremities toward the core to protect vital organs from the cold. This process stimulates the kidneys and fills the bladder. Frequently stopping to urinate can make you feel more cold and stiff.
  • Nausea or gastro-intestinal distress: Stomach and gut problems can lead to a calorie deficit, compromising your ability to burn energy and move well.
  • Mental dullness and drowsiness: You feel “spaced out” and sleepy, and consequently are at risk for making poor decisions such as wrong turns or napping out in the open.
  • Blurred vision: Prolonged exposure to temperatures below 30 degrees can cause irritated, inflamed eyes and in extreme cases can freeze your corneas. If you can’t see, then you’ll definitely have trouble moving well enough to stay warm.

Take Precautions

“A lot of times, elite runners are the worst” about being prepared to prevent getting cold, confused and depleted, says Leo Lloyd, the medical coordinator of the Hardrock 100, who works in emergency medicine and wilderness response in Durango, Colorado.

Experienced and fast runners trust their ability to move quickly, says Lloyd, and they tend to prefer lightweight gear. They might play down the risk of bad weather if they depart when the sun is shining. Consequently, they might not take extra layers of clothing or extra calories that would help them handle situations where they are forced to move slowly in cold conditions.

“Don’t rely on moving quickly, because that could so easily change. All it takes is one ankle roll,” says Lloyd.

Proper gear and fitness, along with thinking ahead, will mitigate many risks, Lloyd adds. Take action before you suffer any symptoms that lead to problems.

For example, if you’re at the base of a 2,000-foot climb and you notice clouds around the summit, recognize that it’ll be colder and perhaps stormy up there. Make a conscious decision to put on a jacket and hat, and eat something, while you’re feeling warm and alert. Other precautions include:

  • Enhance your fitness: Before you attempt a hard-core trek or day-long ultra, be realistic about whether you have the strength and cardio fitness to cover the distance and terrain.
  • Acclimate to the conditions: If you plan to attempt an extra-long, extra-challenging excursion that involves nighttime running, high altitude, river crossings or other risk-heightening conditions, then practice running in those conditions beforehand.
  • Take extra calories and caffeine, and stay hydrated: Your body burns more calories in the cold, so you will need more than you may expect. Eat enough at regular intervals, and drink to thirst, before you feel hungry, thirsty or lightheaded. Save your caffeinated gels for when you’re sleepy.
  • Take extra layers: A windbreaker or even a plastic garbage bag can save you in a storm. Add items to your pack such as hand warmers and a warm hat.
  • Put on extra layers early: Don’t wait until you’re chilled to get your gloves, hat and jacket.
  • Go with someone rather than solo: A friend on a long run, or a pacer in a race, can help get you to a safer situation, such as a lower elevation or an aid station.

Recognize the risks, be proactive and prepare as if you’ll be on the trail in adverse conditions much longer than anticipated. That way, you can prevent or deal with symptoms before they, so to speak, snowball.

Sarah Lavender Smith is a contributing editor at Trail Runner who runs and coaches in the San Francisco Bay Area.

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