Category Archives: Mountaineering

Already an extreme sport, mountaineering at high altitudes adds exponential risk! Know before you go!

High Altitude, Medicine, Mountaineering

La Paz: Healthy Living At 12,000 feet

2 Comments
Dr Gustavo Zubieta-Calleja explains how lessons learned in La Paz can make space exploration easier

I just returned from the “Chronic Hypoxia” conference in La Paz, Bolivia at 12,000 feet elevation (3,640 m). The sponsor and organizers were Drs. Gustavo Zubieta-Calleja and his daughter Natalia Zubieta De Urioste who run the Institute of High Altitude Pulmonology and Pathology there. Presenters and attendees came from 16 countries covering topics ranging from molecular biology to genetics.
Dr. Zubieta previously published a scientific analysis of centenarians living at various altitudes. He compared Santa Cruz, Bolivia, at sea level, with La Paz/El Alto, each with populations of over three million, and found there are eight times more people over 100 years old at high altitude. (BLDE University Journal of Health Sciences, see blog post 1/5/18) Since his father Gustavo Zubieto Castillo founded the institute in 1970, they have been advocates of the health promoting effects of a low oxygen environment.
A presentation on “BioSpaceForming” even identifies chronic hypoxia as a “fundamental tool”, that “gives humans and other species an advantage on earth and beyond.” Dr Zubieta explained that the space station is engineered to have the barometric pressure (760 mmHg) and oxygen content of sea level. When the astronauts change into their space suits to work outside the ship they experience a pressure drop of over 200 mm Hg in a laborious process of donning the suit. Seeing that millions of inhabitants are healthy at 486 mm HG in Bolivia, he advocates that maintaining lower pressures and lower oxygen levels in the space station would be economical and promote the health of the astronauts. Several altitude scientists see this as a future that “uncouples biology and physics.

Acclimation, Health, High Altitude, High Altitude Training & Fitness, Mountaineering

Rethinking Your Energy Supply

Leave a comment

On May 27th 2017, Adrian Ballinger summited Mount Everest without supplemental oxygen. This is an accomplishment that less than 200 people have achieved and followed a failure to summit the previous May of 2016. The 41 year old seasoned climber attributed his failures to the cold, which could have been aided by more muscle and fat content, better insulated jacket and gloves, but he wondered why his climbing partner, Cory Richards so easily made it to the top. Ballinger came to realize it that wasn’t his gear or body composition, but it was that Richards had a different approach to training and nutrition that gave him the edge to summit. Richards trained with a organization called Uphill Athlete that trains its athletes to become a fat burners. After hearing of Richard’s training regimen Ballinger was determined to pursue the same for a another summit attempt in 2017. Ballinger was a carb burner, which means he was relying on burning carbohydrates for energy. When he attempted to summit Everest being a carb-burner, he simply ran out of energy to fuel his body through the last grueling stretch. This was due to depleted glycogen levels that a carb-burner relies on. The average human can only contain enough carbohydrates to supply glycogen stores for about 45 minutes. Once your glycogen stores are depleted, you need to refuel, which in Ballinger’s case, would mean pulling a hand out of a mit in the frigid Everest air to replenish his energy every 45 minutes. This is also known as “bunking,” which means completely exhausting your energy supply, which is what happened to Ballinger. Richards on the other hand, was a fat burner. With alterations in Ballinger’s nutrition and training regimen, he was successful in 2017.

But what is a fat burner?

A fat burner is an athlete that primarily uses fat for energy, and this metabolic process is called fat oxidation. When an athlete is exercising on a typical high carb and low fat diet, they are burning about a 50/50 mix of carbs and fats during steady exercise. If that athlete decides to sprint at full speed being a carb burner or a fat burner, they are primarily burning carbohydrates, known as glycogen. This is the body’s evolutionary design to have instant energy to run away from the tiger when it storms your cave. In Ballinger’s scenario, the high intensity of Everest climbing was like a sprint, depleting all of his glycogen stores causing him to “bunk”.

Why is a fat-burning diet better for climbing?

Being a fat burner for a long distance endurance athlete is beneficial because it eliminates the need to refuel every 45 minutes, which is bothersome. Ever wonder why there is a plethora of fancy sugary “sports” drinks, gummies, and energy bars at sporting stores? They are called “energy” foods, because they are loaded with simple carbohydrates and sugar. On the other hand, a fat burner does not need refueling foods or drinks during exercise, but relies on the extensive supply of fat throughout the body. Even the most elite athletes with very low body fat will have enough to supply the body energy for a event. Picture this, there is a giant fuel tanker truck cruising on I-70. The truck has its own fuel tank which sits below the cab of the truck, which will be depleted in a couple hours. What if the truck could access the large tank that it’s hauling? That would give the trucker a enough fuel to drive for days! In the context of nutrition and your body, the small tank is the your glycogen storage and the large tank is fat storage. This is why some people can fast for days without skipping a beat; they have tapped into their fat supply.

What does it take to become a fat burner?

To become a fat burner, it’s quite simple: cut the carbohydrates. Well, I guess some may think it’s not so easy. You have to cut out pizza, bread, candy, tortillas, and all that good tasty stuff. When a person limits their carbohydrate intake to less than 10% of caloric intake, and increase fat consumption to 70% of their intake, their body shifts into a different mode of creating energy, by burning fat instead of carbs. The by-products of fat oxidation are called ketones. When a person converts to being a fat burner, it is called being in ketosis. This process may take a few days to weeks, which varies from person to person.

Is there any research behind this crazy idea of eating all the bacon and butter you can handle?

Yes, yes there is!

In the research article by Volek et al. (2015), the authors wanted compare a low carbohydrate ketogenic diet and a typical high carbohydrate diet in 20 elite endurance athletes. The authors tested the athletes with a 180 minute, moderate intensity (64% VO2 max), treadmill run.

VO2 max is known as the capacity of your cardiovascular system and its ability to distribute oxygen throughout the body. Higher means a stronger cardiovascular system, so 64% of your maximum effort would be considered moderate exercise.

A 64% VO2 max to you or I would be a brisk walk or a slow hike up that beautiful 14’er, but for these Ironman athletes it was an easy run on a treadmill. The authors compared the rate of fat oxidation and carb oxidation between the two diets, as well as their ability to recover and replenish their glycogen stores. The authors found that the fat adapted athletes had 2.7 times the rate of fat oxidation than the high carb diet athletes. The low carb group also had fat oxidation at higher VO2 max, meaning they could go faster without tapping into their precious glycogen stores. The study also found that after the exercise, the athletes in both groups had similar glycogen level in their muscle. This is significant because the classic rule of thumb with exercising is that you need a post-workout shake with protein and carbs to replenish your muscles, or your exercising efforts are gone to waste …

WRONG!

It turns out your body has its own way of replenishing its glycogen stores without the post-workout carb load. That means after you climb that 14’er, you don’t necessarily have to stop at the local brewery for carb-tastic IPA, but I won’t judge you if you do.

In another research article by Hetlelid et al., they wanted to compare the levels of fat and carb oxidation levels between nine well-trained (WT) runners and nine recreationally-trained (RT) runners during a high-intensity interval training session (HIIT). There was no difference in diets amongst the participants in the study. The study found that the WT runners had a three times higher rate of fat oxidation than RT runners and increased performance with higher VO2 max. The author attributed the increased performance due to the higher rates of fat oxidation. These athletes were consuming a normal carb-ful diet, which makes me wonder what the difference would have been if they were fat adapted.  

So, let’s get down to why all this mumbo-jumbo is important to your next trip to the high country. Many outdoor activities that we enjoy in the summer like hiking, biking, climbing, etc. all require significant energy to supply for all day fun. Take climbing a 14’er, for example. You will most likely be climbing for several hours, depleting your energy stores as you climb being on a high carb diet. You have to stop, refuel, start up climbing, stop and repeat. As a fat adapted climber, you could sail past your carb-comrades with ease, not depleting your glycogen stores all day, all while burning some of that winter Christmas cookie belly in the process. As we examined the two research articles, we also found that higher fat oxidation could mean higher VO2 max levels.

What does this mean for your next trip to high altitude?

That’s right, better usage of the less available oxygen in the high country and improving oxygen delivery throughout the body. If you want to be the best Balliger you can be on the mountains this summer, rethink your energy supply and consider life in the fat lane! 

So, here are some personal tips to becoming fat adapted:

-Give your body at least 3 weeks to become adapted before any highly strenuous activity, like climbing a 14’er

-Hydrate, hydrate, hydrate with water, and balance it with electrolytes

-Consult with your physician before drastically changing your diet

-Choose foods high in natural fats (eggs, nuts, olive oils, avocados, meat, fish, dairy) and stay away from unhealthy trans fats

-Intermittent fasting can help you transition into ketosis faster (12-16 hrs)

 

References

Hetlelid, K. J., Plews, D. J., Herold, E., Laursen, P. B., & Seiler, S. (2015). Rethinking the role of fat oxidation: Substrate utilisation during high-intensity interval training in well-trained and recreationally trained runners. BMJ Open Sport & Exercise Medicine, 1(1). doi:10.1136/bmjsem-2015-000047

Volek, J. S., Freidenreich, D. J., Saenz, C., Kunces, L. J., Creighton, B. C., Bartley, J. M., . . . Phinney, S. D. (2016). Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism, 65(3), 100-110. doi:10.1016/j.metabol.2015.10.028

http://www.adrianballinger.com/about/

Acclimation, Child Growth & Development, Health, High Altitude, Medicine, Mountaineering

P.L.A.Y. AT ALTITUDE CAMPAIGN

Leave a comment

This summer, as part of my RN to BSN program with UCCS, I needed to complete a public health course with clinical. I decided on an unusual path by joining the team of pediatrician and public health activist, Dr. Ebert-Santos.

Dr. Ebert-Santos has been the primary care giver for my two boys, now 8 and 4 years old, since birth. I would venture to say that Dr. Chris, as we call her, is known by most families in Summit County. Not only are we a mountain community but we are a community committed to growing in mindful ways. A lot of thought goes into how we operate our community events and care for our families. Dr. Ebert-Santos has been very active on more community issues than I can address here. But, let’s include water quality, health insurance/coverage initiatives, and pretty much every community health walk for a cause, healthy community eating and garden initiatives, bike to work week, trail maintenance…you get the picture. For these reasons, I finagled my way into her office this summer.

Our community is one of the healthiest in the nation according to national statistics. We are one of the lowest on obesity, adult diabetes, and hypertension. For this reason, along with the beauty of the Rocky Mountains, we have a lot more people moving here than ever before. “Summit County has recently exceeded a permanent resident population of 30,000. This is a 28.7% increase in full-time residents since 2000” (Summit County Colorado, 2017).

One major health issue that Dr. Ebert-Santos is bringing to light with her current research shows that high altitude kids are often born at lower birth weights, catching up on the national growth charts within the first few years. These babies are not unhealthy by high altitude standards. The problem is that statewide and nationally, we have yet to set standards specific to high altitude children. Dr. Ebert-Santos is making a big push to address this.

Dr. Ebert-Santos is also the doctor most likely to check your newborn for wellness and release them home, safe and sound, following birth. Many of our mountain babies go home with an infant oxygen tank that you will see parents wearing as backpacks. Dr. Ebert-Santos has been collecting and analyzing data on high altitude kids for years now. At higher altitudes, we have lower air pressure and that means decreased bioavailable oxygen. While many people are aware that acute mountain sickness and high altitude pulmonary edema (HAPE) are potential obstacles to overcome when travelling up into the Rockies, many people do not know that our resident children, who haven’t even travelled down from altitude and back up, are also prone to these illnesses. High altitude pulmonary edema in children living at altitude can follow the sort of respiratory infections that kids are prone to catching as they make their way through school while their immune systems are developing. This is often entirely treatable with oxygen alone.

The problem Dr. Ebert-Santos has identified is that, assuming residents are acclimated and therefore unlikely to have HAPE, kids here are often diagnosed with pneumonia instead of HAPE. Treatment of pneumonia often involves a hospital stay with antibiotics and other medications on board. Dr. Ebert-Santos sees dozens of children each year who have what she would like others in the medical community to recognize as Mountain Resident HAPE. With proper diagnosis, these children can be treated with oxygen and improve within a matter of days. Awaiting recovery from pneumonia when there is no pneumonia present can be detrimental to children.

Dr. Ebert-Santos will have her research published this year in the Journal of High Altitude Medicine and Biology. I had the fortunate experience of working this summer, with Dr. Ebert-Santos and her dedicated team, to create a public health message relevant to her work. Office manager Meaghan Zeigler, who has a master’s in public health, was invaluable to my education there.  I was happy to find that our local oxygen companies were ready to join in this effort to educate the public. Big thanks to Summit Oxygen Inc. in Frisco, AlpinAire in Breckenridge, and AeroCare in Silverthorne! Below you can see the acronym I created to help high altitude families recognize the signs and symptoms of high altitude illnesses, including HAPE and Mountain Resident HAPE.

Stay safe and keep breathing Summit County!

Juli Joyce, RN

 

Acclimation, Child Growth & Development, Health, High Altitude, High Altitude Training & Fitness, Mountaineering

Can I take my child up a 14er?

Leave a comment

There are over fifty 14ers in Colorado. A 14er is a mountain with an elevation of at least 14,000 feet. If summited, these majestic peaks afford their climbers spectacular views of the surrounding landscape. Being that many people within Colorado – and those who come to visit – are active, a question often voiced by parents is: “Can my child hike up a 14er with me?” Unfortunately, there is no straightforward answer to this question and the simplest response is: it depends.

According to recent research, it appears that children are largely similar to adults when it comes to adapting to higher elevations. Research examined children’s short-term cardiorespiratory adaptation, incidence of acute mountain sickness, hypoxic ventilatory response, and maximal exercise capacity and found little variance between adults and children (Garlick, O’Connor, & Shubkin, 2017).

When CAN you take your child up a 14er? There are a multitude of factors that affect when and if a child can climb a 14er. For example, children develop and mature at different rates. This might affect whether your 11-year-old is able to climb a 14er, compared to someone else’s 11-year-old. Additionally, some children grow up being exposed to technical hikes and climbs, while others are not. This affects ability level and is certainly something to keep in mind (Provance, n.d.). Another factor to keep in mind is whether you’re child has an underlying condition. For example, conditions such as congenital heart disease, asthma, sickle cell anemia, an upper respiratory infection, or an ear infection can significantly increase the risk for high altitude illnesses (Garlick, O’Connor, & Shubkin, 2017, p. 6). Yet another factor is whether you live at altitude or are visiting from a lower elevation. There is a strong recommendation for those individuals traveling from a lower altitude to take some time to acclimate. Spending a night or two at an intermediate altitude is recommended. Additionally, be mindful not to overdo it when you do ascend to a higher elevation: stay hydrated and don’t overexert yourself. If you decide to climb a 14er, it is imperative that you give your body at least a few days to acclimate to the altitude (“How can I optimize my health at high altitude?”, 2016).

So, what’s the bottom line? Since it isn’t possible to place a concrete age on when it’s okay for your child to climb a 14er, it is ultimately up to you to know you’re child’s limits and to decide if such a challenging hike is right for you and them. The most important thing is to make sure that everyone remains safe.

If you do decide to set out on the challenge of hiking up a 14er, there are some things to remember in order to keep yourself and your child as safe as possible and ensure that the hike is an enjoyable experience for all (Kirkland, 2015):

  • Set out early: Summiting the peak by noon is recommended in order to avoid afternoon weather, thunderstorms, and potential lightning strikes.
  • Start slow and easy: It’s important for you to determine whether or not you’re child will be able to summit a 14er. Start with easy hikes and build up over time so that you have a good understanding of your child’s abilities.
  • Know the weather forecast: Check the weather before you set out to prevent getting stuck in a storm.
  • Clothing: Wear appropriate clothing. It is important to layer since it can be colder on top of the mountain. Additionally, it is important to wear clothing that protects you from the elements (including the sun!).
  • Protect yourself from the sun: The sun can be very strong when one is high up. It is very important to ensure that your child is adequately protected from the sun: sunscreen, clothing, etc.
  • Food and Fluids: Bring adequate nutrition and hydration.
  • Be prepared to turn around ahead of time: There are many things that could cause you to turn around. It’s very important to accept ahead of time that you might not manage to summit the peak and to accept that’s okay.
  • High altitude illness: It is incredibly important for you to know the symptoms of high altitude illness and be prepared to turn around should your child exhibit any of them. Symptoms of high altitude illness include: fussiness or irritability, refusal to eat, lack of energy, nausea and/or vomiting, dizziness, and light headedness (Provance, n.d.).

References:

Garlick, V., O’Connor, A., & Shubkin, C. D. (2017). High-altitude illness in the pediatric population: A review of the literature on prevention and treatment. Current Opinion in Pediatrics, doi:10.1097/MOP.0000000000000519

How can I optimize my health at high altitude? (2016). Retrieved from http://www.altitudemedicine.org/optimizing-health-at-altitude/

Kirkland, E. (2015, May). Taking kids to new heights: Hiking Colorado’s “14er” mountains. Retrieved from http://www.outdoorfamiliesonline.com/hiking-colorados-14er-mountains/

Provance, A.J. (n.d.). What age can my child start hiking fourteeners? Retrieved from https://www.childrenscolorado.org/conditions-and-advice/new-and-featured-articles/sports-safety/when-can-kids-start-hiking-fourteeners/

Rianne Smeele, BSN, RN, Regis University FNP Student

Acclimation, Child Growth & Development, Health, High Altitude, High Altitude Training & Fitness, Medicine, Mountaineering

Slumber Up: Sleeping at High Altitude

Leave a comment

 

Does high altitude affect sleep quality? The answer is that for some, it does. If you’ve ever quickly arrived to the mountains on a ski or summer getaway, you may have experienced fitful and non-restful sleep. Individual responses to high altitude may vary, however there is an understood physiological basis for sleep disruption at altitude.

 

A phenomenon known as “periodic breathing of altitude” is commonly experienced above 2500 m of elevation (about 8200 ft) in those not previously acclimatized [2]. This is a common sleep elevation in Colorado mountain towns such as Frisco, Colorado (proud home to this blog!). Periodic breathing of altitude may be more likely to occur as sleeping altitude increases. Here’s the science behind it:

 

The decreased atmospheric pressure at altitude results in less oxygen driven into the lungs and through to the bloodstream. The body attempts to compensate by increasing the rate of breathing (tachypnea), which also causes more carbon dioxide to be exhaled. Chemoreceptors sense the decrease in carbon dioxide and signal the body to stop breathing temporarily (apnea) to correct the imbalance. Alternating cycles of tachypnea and apnea continue to occur during sleep. The result is decreased REM sleep, which is a critical restful and rejuvenating phase [2].

 

Worried about your next sleepless night on a mountain trip? Fortunately, there’s acetazolamide (Diamox). It is a carbonic anhydrase inhibitor that works by eliminating bicarbonate in the urine, which is a base. The body subsequently becomes more acidic, and that acid in the bloodstream is readily converted to carbon dioxide. The body is “tricked” into thinking that there is plenty of carbon dioxide present in the bloodstream, and periods of apnea during sleep may be reduced or eliminated [3].

 

To help prevent periodic breathing of altitude, adults can take acetazolamide preferably starting on the day before ascent or on the first day at altitude. Adults typically take 125 mg twice a day until either 3 days at altitude has been reached or descent back down has occurred [1]. Ask your healthcare provider about what’s right for you. Consider acetazolamide next time you’re sleeping up high, and get that refreshing sleep that allows you to better enjoy the things you love at altitude!

 

-Justin Murphy, PA-S

Red Rocks Community College Physician Assistant Program

Clinical Rotation- May 2017

 

References

1) Athena Health (2017). Acetazolamide generic. Epocrates Online. Retrieved from: https://online.epocrates.com/drugs/12701/acetazolamide/Adult-Dosing

2) Gallagher, S. A., Hackett, P., & Rosen, J. M. (2017). High altitude illness: Physiology, risk factors and general prevention. Up To Date, Topic 181,  Version 20.0.  Retrieved from: https://www.uptodate.com/contents/high-altitude-illness-physiology-risk-factors-and-general-prevention?source=search_result&search=high%20altitude%20sleep&selectedTitle=2~150

3) Winter, C. (2016). Sleeping around: How to sleep at high altitude. Huffington Post. Retrieved from: http://www.huffingtonpost.com/entry/sleeping-around-how-to-sleep-at-high-altitude_us_5806da29e4b08ddf9ece1228?ncid=engmodushpmg00000006

Acclimation, Health, High Altitude, High Altitude Training & Fitness, Medicine, Mountaineering

Live High Train Low- What’s an athlete to do?

Leave a comment

I just came across this study in the literature from a couple years ago

Optimizing Altitude for Live High-Train

Low (LHTL) Training

Chapman et al (2013) hypothesized that athletes living at

higher altitudes would experience greater improvements in sea

level performance, secondary to greater hematological acclimatization,

compared to athletes living at lower altitudes. After

4 weeks of group sea level training and testing, 48 collegiate

distance runners (32 men, 16 women) were randomly assigned

to one of four living altitudes (1780m, 2085m, 2454m, or

2800 m). All athletes trained together daily at a common altitude

from 1250m to 3000m following a modified LHTL

model. Subjects completed hematological, metabolic and

performance measures at sea level before and after altitude

training. Upon return from altitude, 3000m time-trial performance

was only significantly improved in groups living at the

middle two altitudes. EPO remained elevated after 72 h except

in the 1780m group. Erythrocyte volume was significantly

higher in all groups but not different between groups. These

data suggest that a 4 week LHTL altitude camp at 2000m to

2500m is optimal for sea level performance.

 

HIGH ALTITUDE MEDICINE & BIOLOGY

Volume 15, Number 1, 2014

ª Mary Ann Liebert, Inc.

DOI: 10.1089/ham.2014.1513

4

 

Acclimation, Health, High Altitude, High Altitude Training & Fitness, Medicine, Mountaineering

How Long With Low Oxygen?

Leave a comment

We frequently measure oxygen levels on people of all ages here in our mountain clinics. We order nighttime oximetry and sleep studies and analyze hundreds of data points reflecting heart rate and oxygen levels over time. When we see someone with a low oxygen in clinic, there may be no way of knowing if they have been hypoxic for hours, days, weeks unless they have an illness with an abrupt onset, like influenza or pneumonia or they just returned from sea level. Babies during the first weeks may have low oxygen with no symptoms, since they are accustomed to this in the womb where oxygen saturations run 40-60 %.

A recent article in the Journal of the American Medical Association studied extremely premature babies at 18 months for adverse outcomes including vision, hearing, cognition, motor, and language. They correlated the degree of disability with the length of time the child was hypoxic during the first few months. One minute of hypoxia seemed to be the cut-off. Now this doesn’t tell us how low or how many but it may be a helpful guide when watching someone’s oxygen or analyzing a sleep study. Shorter episodes may be insignificant long term.

This is a complex article and the children with the poorer outcomes had more episodes of hypoxia at older ages- 9-10 weeks after birth. This could mean that the insult to the brain was contributing to the hypoxic episodes as well as the deficits.

 

Acclimation, Health, High Altitude, High Altitude Training & Fitness, Medicine, Mountaineering, Technology

Does sleeping on oxygen at high altitude improve athletic performance?

Leave a comment

I have read many scientific studies on athletic performance at altitude. Active high altitude residents are always looking for ways to improve. As we age we experience a loss of speed and endurance, even with regular training. Some of this is inevitable, but how can we know if there is something else affecting our fitness?

I started sleeping on oxygen 9 months ago because of high blood pressure, which was instantly cured. Now I find that my strength and endurance have improved during the last few months. For example, I was rowing 13400 meters per hour with several brief pauses last fall, and now I am at an all-time high of 14100 m per hour with one pause. My running feels better, I’m back up to 6 miles from 4.

There are other factors that could influence this. In 2012-2013 I was on 17 pills including prednisone and had four surgeries for tongue cancer and myasthenia gravis. I was able to continue working out daily although part of that was less intense, such as yoga. I also had rotator cuff surgery. So my current fitness improvement could just be a rebound from overcoming those health conditions.

The only way to know for sure is to do a randomized controlled double blind study of athletes performance on and off nightly oxygen, or study the same athlete with and without oxygen. This is not an immediate effect, so months or years of observation and measurements would be needed.

In the meantime, if you live above 2500 meters/9000 feet and are losing stamina or strength consider having a night time pulse oximetry test to check for hypoxia during sleep.

Acclimation, Health, High Altitude, High Altitude Training & Fitness, Mountaineering

Kilimanjaro

7 Comments

Overflow crowd tonight at St. John’s church where Katherine Jeter shared her story of climbing Mt Kilimanjaro with others from the county, celebrating her 75th birthday that year. I am so inspired by the people older than I am who are challenging themselves like this. This peak is a mile higher than our 14er’s! The average age in this group was 65. Using acetazolamide/Diamox helped many of the climbers.